LITERATURE REVIEW OF SCIENTIFIC STUDIES SUPPORTING THE EFFICACY OF MANDIBULAR TRACKING IN THE DIAGNOSIS AND TREATMENT OF TMD

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INTRODUCTION

Progress in the field of mandibular tracking was limited by the capability of available instrumentation. As early as 1931 Hildebrand used cinematography of a moving reflective point to track mandibular movement (1). Cineflourography was used by Klatsky in 1941 (2) and was followed by Kurth‟s use of stroboscopic photography in 1942 (3). Mechanical tracking has also been used by several investigators throughout the history of mandibular tracking in dentistry (4). The interference of mechanical tracking devices with normal mandibular function was a common problem. The first use of electronic recording techniques to record occurrence and duration of occlusal contacts during mastication was reported in 1953 (5). Brewer and Hudson later used miniaturized make or break switches to study tooth contact (6). Adams and Cannon developed instrumentation to trace actual movement patterns of the mandible during functional and parafunctional movements (7, 8).
In 1975 Jankelson defined the requirements and criteria for a mandibular tracking system that would provide reliable quantitative and reproducible data. The criteria are:

1. The relationship of the mandible to the maxilla must be determined in three dimensions.

2. Data output must be continuous to permit analysis of the dynamic components of mandibular function.

3. The system cannot encroach on the occlusal plane so as to interfere or alter proprioception.

4. To avoid unnatural proprioceptive input and minimize mechanical limitations on mandibular movement, no supporting structures or wires should protrude from the mouth.

5. The practical use of the system requires that setup time be minimal and that the system be self contained.

6. Measurement in the vicinity of the occlusal plane should be accurate to within 0.1mm.

7. The system should be widely available and operable by dental personnel (9).

Belser and Hannam demonstrated that an early model Myo-tronics Kinesiograph was capable of recording incisal point movement to within 0.3mm anywhere within the envelope of chewing (10). The same authors have used this instrumentation in other scientific studies, demonstrating their confidence in the capability and accuracy of this modality (11).

Today‟s Mandibular Kinesiograph is a computerized electronic measuring device that can track mandibular movement with 0.1mm plus or minus accuracy in three simultaneous planes as well as precisely measuring opening and closing velocity.

The value of this measurement capability to the clinical dentist responsible for establishing a predictable and accurate occlusal position diagnostically and therapeutically is self evident. The ability to record, measure and capture a desired occlusal position transcends occlusal philosophy.

The value of correlative data utilizing the MKG was emphasized in an AADR 1983 report by Bigelow, Slagle, and Chase, Department of Oral and Maxillofacial Surgery, University of Tennessee, entitled “Evaluation of Internal Derangement of TMJ with Mandibular Kinesiograph/ Arthrography” (25).

The report stated:
“Arthrography has established the increasing frequency of internal derangement of the TMJ. Jankelson et al have developed the Mandibular Kinesiograph (MKG) to characterize abnormalities of the TMJ. This study demonstrates a positive correlation between patients with stages of internal derangements and diagnostic MKG tracings. 20 patients were examined in this study. Historical, physical and radiographic criteria were used to diagnose patients with internal derangement of the TMJ. Arthrography was then performed to evaluate the extent of abnormalities. Patients were grouped according to the presence of clicks on opening, closing or both. Also on arthrography findings: normal, anterior dislocation with reduction, or anterior dislocation without reduction. Velocity tracing of the MKG were compared concerning characteristic and morphologic patterns. The velocity tracings were classified according to the irregularities in the opening and closing velocities. Correlations occur between velocity tracings and the arthrogram presentation of internal derangement which resulted in reduction or nonreduction during jaw excursions. Patients with arthrographic diagnosis of internal derangement without reduction demonstrated MKG tracings of impaired vertical opening deviation toward the affected side and characteristic irregularities in the velocity tracing. Patients with reduction showed only deviation to the affected side. MKG evaluation appears to be a reliable means to diagnose internal derangement of the TMJ.”

Following are controlled studies that further support the rationale for mandibular jaw tracking. The Mandibular Kinesiograph is a measurement modality. Measurement is the common index for all scientific disciplines. The evolution of every scientific discipline has depended upon development of improving measurement modalities. The literature is clear that dentistry is no exception.

INTRODUCTION TO MANDIBULAR TRACKING

SUPPLEMENTAL REFERENCES

1. Hildebrand, G.Y. Studies in masticatory movement of the human lower jaw. Scand. Arch. of Physio. Vol. 3, 1931.

2. Klatsky, M.A. A cineflourographic study of the human masticatory apparatus in function. Am. J. of Ortho. and Oral Surg. 26:664, 1941.

3. Kurth, L.E. Mandibular movements in mastication. JADA. 29:1769, 1942.

4. Boswell, J.V. Practical occlusion in relation to complete dentures. J. of Prosth. Dent. 1:307, 1951.

5. Jankelson, B., Hoffman, G.M. and Hendron, J.A. Physiology of the stomatognathic system. JADA. 46:375, 1953.

6. Brewer, A.A. Hudson, D.C. Application of miniaturized electronic devices to the study of tooth contact in complete dentures. J. Prosth. Dent. 11:62, 1961.

7. Adams, S.H. and Zanders, H.A. Functional tooth contacts in latent and in centric occlusion. JADA. 69:465, 1964.

8. Cannon, D.C., Reswick, J.B. and Messerman, T. Instrumentation for the investigation of mandibular movements. Report No. EPC464-8, Cleveland Engineering Design Center, Case Western Reserve Univ., 1964.

9. Jankelson, B., Swain, C.W., Crane, P.F. and Radke, J.C. Kinesiometric Instrumentation: A New Technology. JADA. 90:834-840, 1975.

10. Belser, U.C. and Hannam, A.G. Influence of altered working-side occlusal guidance on masticatory muscles and related jaw movement. J.Prosth. Dent. Vol. 53, No. 3, pp 406-413, March 1985.

11. Belser, U.C. and Hannam, A.G. The contribution of the deep fibers of the masseter muscle to selected tooth-clenching and chewing tasks. J.of Prosth. Dent. Vol. 56, No. 5, pp 629-635, Nov. 1986.

12. Feine, J.S., Hutchins, M.O. and Lund, J.P. “An evaluation of the criteria used to diagnose mandibular dysfunction with the mandibular kinesiograph.” .JADA. Vol. 60, No. 3, Sept. 1988.

13. Gibbs, C.H., et al. Functional movements of the mandible. J. Prosth. Dent. 26:604-619, Dec. 1971.

14. Clark, G.T. and Lynn, P. Horizontal plane jaw movements in controls and clinic patients with temporomandibular dysfunction. 55:730-735, 1986.

15. Monteiro, et al. Relationship between mandibular movement accuracy and masticatory dysfunction symptoms. J. of Cranio. Disorders: Facial and Oral Pain. Vol. 1, No. 4, pp 237-242, 1987.

16. Rosenbaum, M. The feasibility of a screening procedure regarding temporomandibular joint dysfunction. J. Oral Surg. 39:382-389, March 1975.

17. Rieder, C.E. Maximum mandibular opening in patients with and without a history of TMJ dysfunction. J. Prosth. Dent. Vol. 39, No. 4, pp 441-446, April 1978.

18. Balthazar, Y., et al. Limited mandibular mobility and potential jaw dysfunction. J. Oral Rehab. Vol. 14, pp 569-574, 1987.

19. Jemt, T. and Hedegard, B. Reproducibility of chewing rhythm and of mandibular displacements during chewing. J. Oral Rehab. Vol. 9, pp 531- 537, 1982.

20. Shields, et al. Using pantographic tracings to detect TMJ and muscle dysfunctions. J. Prosth. Dent. 39:80-87, 1978.

21. Van Willigen, J. The sagittal condylar movements of the clicking temporomandibular joint. J. Oral Rehab. 6:167-175, 1979.

22. Lederman, K. and Clayton, J. Patients with restored occlusions. Part I: TMJ dysfunction determined by a pantographic reproducibility index. J. Prosth. Dent. 47:198, 1982a.

23. Lederman, K. and Clayton, J. Restored occlusions. Part II: The relationship of clinical and subjective symptoms to varying degrees of TMJ dysfunction. J. Prosth. Dent. 47:304, 1982b.

24. Monteire, A.A., et al. Relationship between mandibular movement accuracy and masticatory dysfunction symptoms. J. Craniomand. Disord.: Facial and Oral Pain. 1:237-242, 1987.

25. Bigelow, W.C., Slagle, W.F. and Chase, D.C. Evaluation of internal derangement of TMJ with mandibular kinesiograph/arthrography. AADR Abstracts. No. 675, 1983.

ARTICLES REVIEWED IN THIS PUBLICATION

SECTION 1: STUDIES THAT DOCUMENT JAW TRACKING (CMS) ACCURACY

1. Wessberg, G.A., Epker, B.N., and Elliott, A.C. The reliability of a Mandibular Kinesiograph. Hawaii Dental Journal, Vol. 15, No. 3, September 1984. See abstract page 142.

2. Jankelson, B. and Swain, C.W., et al. Kinesiometric instrumentation: a new technology. Journal of the American Dental Association, Vol. 90, pp 834-840, April 1975. See abstract page 144.

3. McMillan, D.R. and McMillan, A.S. A comparison of habitual jaw movements and articulator function. Acta Odontol Scand. (1986) 44, 291- 299. Oslo. ISSN 0001-6357. See abstract page 145.

4. Hannam, A.G., DeCou, R.E., Scott, J.D. and Wood, W.W. The kinesiographic measurement of jaw displacement. J. of Prosthetic Dentistry. Vol. 44, 88-93, July 1980. See abstract page 146.

SECTION 2: STUDIES THAT DOCUMENT THE VARIATION IN MANDIBULAR FUNCTION IN NORMAL VERSUS ABNORMAL POPULATIONS

1. Maruyama, T., Miyauchi, S., Umekoji, E. and Simoosa, T. Analysis of the relationship of centric relation and centric occlusion by the Mandibular Kinesiograph. J. Osaka Univ. Dent. Sch. Vol. 20, 173-178, 1980. See abstract page 148.

2. McCall, W.D., Jr., Bailey, J.O., Jr., and Ash, M.M., Jr. A quantitative measure of mandibular joint dysfunction: Phase plane modelling of jaw movement in man Archs Oral Biol. Vol. 21, pp 685 – 689. Pergamon Press 1976. Printed in Great Britain. See abstract page 150.

3. Griffin, C.J. Diagnosis and treatment of mandibular displacements by mandibular kinematography. The dental nociceptive reflex. Australian Dental Journal. pp 384-392, Oct. 1963. See abstract page 152.

4. Mongini, F.. A graphic and statistical analysis of the chewing movements in function and dysfunction. The J. of Cranio. Pract. Vol. 2, No. 2, March-May 1984. See abstract page 154.

5. Ow, R.K.K., Carlsson, G.E., and Jemt, T. Craniomandibular disorders and masticatory mandibular movements. J. of Craniomandib. Disord.: Facial & Oral Pain. 1988; Vol 2, No. 2, 96-100. See abstract page 156.

SECTION 3: STUDIES THAT DOCUMENT THE CLINICAL EFFICACY AND VALIDITY OF MANDIBULAR TRACKING

1. Jankelson, B. Three dimensional orthodontic diagnosis and treatment: A neuromuscular approach. J. of Clinical Orthodontics. Vol. XVIII, No. 9, Sept. 1984. See abstract page 158.

2. Callender, J.M. Orthodontic application of the Mandibular Kinesiograph: Part II. J. of Clinical Orthodontics. Vol XVIII, No. 11, pp 791-805, Nov. 1984. See abstract page 159.

3. Callender, J.M. Orthodontic application of the Mandibular Kinesiograph: Part I. J. of Clinical Orthodontics. Vol XVIII, No. 10, pp 710-718, Oct. 1984. See abstract page 204.

4. George, J.P., and Boone, M.E. A clinical study of rest position using the Kinesiograph and Myomonitor. The Journal of Prosthetic Dentistry. Vol. 41, No. 4, pp 456-462, April 1979. See abstract page 162.

5. Konchak, P.A., Thomas, N.R., Lanigan, D.T., and Devon, R. Vertical dimension freeway space, a kinesiographic study. The Angle Orthodontist. pp 145-154, April 1987. See abstract page 165.

6. Wessberg, G.A., Epker, B.N., and Elliott, A.C. Comparison of mandibular rest positions induced by phonetics, transcutaneous electrical stimulation, and masticatory electromyography. The Journal of Prosthetic Dentistry. Vol. 49, No. 1, pp 100-105, January 1983. See abstract page 167.

7. Crandall, J.A. Evaluation of mandibular movement and range of motion in the diagnosis of craniomandibular disorders. J. of Craniomandib. Pract. Vol. 4, No. 3, pp 234-245, July 1986. See abstract page 168.

SECTION 4: STUDIES UTILIZING MANDIBULAR TRACKING FOR RESEARCH PROTOCOLS

1. Belser, U.C., and Hannam, A.G. The influence of altered working-side occlusal guidance on masticatory muscles and related jaw movement. The Journal of Prosthetic Dentistry. Vol. 53, No. 3, pp 406-413, March 1985. See abstract page 170.

2. Konchak, P., Thomas, N., Lanigan, D., and Devon, R. Freeway space measurement using mandibular Kinesiograph and EMG before and after TENS. The Angle Orthodontist. pp 343-350. See Abstract on page 171.

3. Hannam, A.G., et al. The relationship between dental occlusion, muscle activity and associated jaw movements in man. Archives Oral Biol. 22:25, 1977. See abstract page 174.

4. Belser, U.C., and Hannam, A.G. The contribution of the deep fibers of the masseter muscle to selected tooth-clenching and chewing tasks. J of Prosthet Dent. Vol. 56, No. 5, pp 629-635, Nov. 1986. See abstract page 177.

5. Nielsen, I.L., Ogro, J., McNeill, C., Danzig, W.N., Goldman, S.M., and Miller, A.J. Alteration in proprioceptive reflex control in subjects with craniomandibular disorders. J. of Craniomandibular Disorders: Facial and Oral Pain. Vol. 1, No. 3, pp 170-178, 1987. See abstract page 178.

6. Neill, D.J. and Howell, P.G.T. Computerized kinesiography in the study of mastication in dentate subjects. J. of Prosthet. Dent. Vol. 55, No. 5, pp 629-638, May 1986. See abstract page 181.

7. Hannam, A.G., Scott, J.D., and De Cou, R.E., A computer-based system for the simultaneous measurement of muscle activity and jaw movement during mastication in man. Archs Oral Biol. Vol. 22, pp 17-23, Pergamon Press, 1977. See abstract page 183.

STUDIES THAT DOCUMENT JAW TRACKING (CMS) ACCURACY

Wessberg, Epker and Elliot evaluate the Mandibular Kinesiograph and conclude that it is far superior to conventional methods of direct measurement despite the inherent non-linearity at wide openings for C.O. The accuracy, reproducibility and linearity make the instrument valuable for clinical purposes.

Wessberg, G.A., Epker, Bruce, N., and Elliott, A.C. The reliability of a Mandibular Kinesiograph. Hawaii Dental Journal. Vol 15, No. 3, September 1984.

ABSTRACT

Reliable and physiologically compatible measuring devices are essential to clinically relevant studies of the human stomatognathic system. This investigation was done to evaluate the accuracy, reproducibility, and linearity of one such instrument, a mandibular kinesiograph. This electronic device was found to be accurate to 4.4 percent of vertical mandibular displacement with clinically tolerable variations in reproducibility and linearity. Despite this variability, the kinesiograph appears far superior to conventional methods of direct measurement of a biologically dynamic entity such as the mandibular rest position.

SUMMARY
The clinical reliability of a mandibular kinesiograph was evaluated on the basis of accuracy, reproducibility, and linearity. Although the statistical analysis reveals this instrument to be inherently inaccurate and nonlinear, it is still a valuable apparatus for specific types of clinical investigation. Therefore, the tremendous physiologic advantage of indirect measurement of mandibular movement demonstrated by the kinesiograph is superior to other methods presently available.

ACCURACY
The overall accuracy of the mandibular kinesiograph was determined by analyzing the difference between the actual vertical displacement of the mandibular incisor tooth induced by the occlusal jig and the indirect measurement displayed on the kinesiograph for the five subjects at the five trials at each of the four vertical positions. The mean error for these 100 recordings was +4.4 percent. In addition, tolerance intervals were calculated to predict the accuracy of a solitary clinical trial (Table 1). These calculations revealed that a 95 percent level of confidence may be assumed for 95 percent of the readings within an interval of -15.8 percent to +24.6 percent (Dixon, W.3., and Massey, F.J., 1969).

Barlett‟s test for homogenicity of variance showed that the variance decreased significantly (p < 0.001) from the 3-millimeter position to the 15- millimeter position. Thus, the graph in Fig. 3 suggests that accuracy improves as the vertical displacement of the mandible increases.

REPRODUCIBILITY:
The reproducibility of the kinesiograph within a single position was determined by analyzing the accuracy for each subject at the four positions of vertical displacement. The percentage of error calculated for the 25 trials at each position and the tolerance interval for a 95 percent level of confidence for 95 percent of the trials are listed in Table 1. These results are also illustrated graphically for each of the five subjects in Fig. 4.

LINEARITY:
The linearity of the kinesiographic recordings from 3 to 15 millimeters was examined by plotting the mean values obtained for each subject at each of the four positions of vertical displacement. These values are illustrated graphically in Fig. 4. The gray area adjacent to the line connecting these mean values represents two standard errors of the mean. There was no statistical support to conclude that the relationship was linear.

DISCUSSION
The results of this study reveal the clinical reliability of a mandibular kinesiograph. The accuracy, reproducibility, and linearity of this instrument were evaluated by conducting five separate trials at four fixed distances of vertical mandibular displacement in five individuals.

The accuracy of the kinesiograph was determined to be 4.4 (T.I. = -15.8, 24.6) percent at the 95 percent level of confidence for 95 percent of the measurements within the parameters studied. Jankelson reported an accuracy of -3 percent at 20 millimeters of vertical displacement (Jankelson, B.; Swain, C.W.; Crane, P.F.; and Radke, J.C., 1975). Hannam et al. employed a micromanipulator to bench-calibrate a kinesiograph and reported an accuracy of +0.25 millimeters anywhere within a spatial column 20x20x40 millimeters (Hannam, A.G.; Scott, J.D.; and Dc Cou, R.E., 1977). These authors did not report a confidence level with their values for comparison with our values.

The gain setting is probably the cause of the apparent increase in accuracy with an increase in the vertical mandibular displacement. A gain of 1 was employed for measurements of 3 and 5 millimeters, a gain of 2 for 10 millimeters, and a gain of 5 for 15 millimeters. The need to increase the gain to permit measurement of these greater distances minimizes the variability.

The reproducibility of the kinesiograph was determined to be 6.6 (T.I. = 24.9, 38.1) percent at 3 millimeters and 2.7 (T.I. = 10.8, 16.2) percent at 15 millimeters at the 95 percent level of confidence for 95 percent of the measurements. Hannam et al. reported a reproducibility of 2.1 percent at 20 millimeters of vertical displacement after five trials on one subject. Again, no level of confidence was reported for this value.

Jankelson and Swain introduce a method of monitoring mandibular movement in three planes by use of magnetometers. The magnetometers sense change in the magnetic field which results from movement of a permanent magnet attached to the lower incisors. In this manner, jaw movement is tracked vertically, anteroposteriorly and laterally in addition to measuring mandibular acceleration. This study published in the Journal of the American Dental Association was the first to introduce the capabilities of the Mandibular Kinesiograph for clinical diagnosis and research.

Jankelson, B., and Swain, C.W., et al. Kinesiometric instrumentation: A new technology. Journal of the American Dental Association. Vol 90, pp 834-840, April 1975.

SYSTEM DESCRIPTION AND THEORY OF OPERATION

The Mandibular Kinesiograph pictured in Figure 1 is the result of system evolution over several years. The system senses the spatial location of a permanent magnet that is mounted on the mandibular incisors with a dental plastic as shown in Figure 2. (setup time for each patient is about three minutes.) The system does not alter proprioceptive input either by interfering with the occlusal plane or by limiting the normal range of mandibular function.

The Mandibular Kinesiograph provides an accuracy of 0.1 mm for resolution of mandibular positions in the vicinity of occlusion. At a vertical opening of 20 mm, the geometric error is approximately -3% in the vertical channel, +5.7% in the anteroposterior channel, and, of course, 0% in the lateral channel because of its differential nature. There is, however, a corresponding gain-loss error in the lateral channel of abut -6% when the mandible is deviated 10 mm left or right at a 20 mm vertical opening; (that is, if the jaw is positioned 10 mm to the left of center at a 20 mm vertical opening, the Kinesiograph will read out a 9.4 mm change in lateral position to the left).

For increased accuracy with large motions away from occlusion, a computer program has been written and is in use, according to an oral report by A. Hannam, department of oral biology, University of British Columbia, that corrects the system errors to a maximum of 0.5 mm anywhere within a 40 mm vertical opening, for + or – 10 mm of anteroposterior motion, and 10 mm left or right; this more than covers the range of function.

SUMMARY

The development of the Mandibular Kinesiograph presents dental professionals with a convenient, physiologically commutable method of monitoring mandibular movements. The analysis of mandibular kinesiology during mastication, deglutition, and speech has already shown itself to be a fruitful area of inquiry. Innovative use of this system in the research and diagnostic environment will undoubtedly provide clinicians with the data base necessary to evaluate individual patient records.

McMillan and McMillan, in a controlled study utilizing the Mandibular Kinesiograph to record three dimensional mandibular movement, conclude “Identification of errors in the recording of direction and magnitude of movements of an incisal point by the Kinesiograph does not detract from its utility or importance as an instrument by means of which movements of the mandible can be visualized quantitatively and qualitatively in three orthognathic planes.

McMillan, D.R., and McMillan, A.S. A comparison of habitual jaw movements and articulator function. Acts Odontol Scand. 1986; 44:291-299. Oslo. ISSN 0001-6357.
Inherent in adjustable articulators are errors related either to recordings from the patient or to adjustments to the instrument, or both. Furthermore, the validity of the geometric concepts on which the, design of these instruments is based, stressing the dominant role of the temporomandibular joints in mandibular movements, is open to question. Microchip technology now makes it possible to view jaw movements in three dimensions while impeding physiological activity minimally. Using a kinesiograph, young dentate Swedish and Chinese adults were examined on two occasions, and the magnitude and direction of some jaw movements were recorded. The results showed that voluntary opening and closing excursions of the mandible frequently followed disparate paths and that closure from the rest position to occlusion was three-dimensional, a lateral component of movement being usual. Retruded contact position was both uncomfortable and unstable. These findings suggest that current procedures for designing and refining occlusal schemes on articulators are invalid. Articulators; dental occlusion; prosthetics.

DISCUSSION

Identification of errors in the recording of the direction and magnitude of movements of an incisal point by the kinesiograph does not detract from its utility or importance as an instrument by means of which movements of the mandible can be visualized qualitatively and quantitatively in three orthogonal planes. This is particularly the case in relation to three-dimensional movements that occur in close proximity to the intercuspal position, where the instrument error is minimal.

CONCLUSIONS

No evidence emerged to suggest that the mandibular movements executed by the subjects in this study occurred about a single, fixed hinge axis. The occlusal terminus for movements was at the intercuspal position. Motion from RP to ICP involved a lateral component of movement in addition to those in vertical and horizontal directions. Voluntary retrusive movement from ICP to RCP also incorporated a lateral component, as did protrusive movements. Retruded contact position was both strained and unstable. Whereas articulators are useful in tooth setting and in designing of occlusal schemes for fixed prostheses, their use in diagnosis and the ultimate refinement of occlusion may introduce errors rather than facilitate their removal, since they cannot mimic the crucial threedimensional movements required.

Hannam, et al, presents a method to help linearize kinesiograph measurements. A thorough analysis of kinesiograph capabilities and limitations is presented in this study. The study concludes that day to day expression with acceptable error of measurement of linear incisor movement can be achieved with the kinesiograph.
Hannam, A.G., DeCou, R.E., Scott, J.D. and Wood, W.W. The kinesiographic measurement of jaw displacement. J. of Prosthetic Dentistry. Vol. 44:88-93, July 1980.
Functional movements of the jaw have been recorded by a variety of methods including direct observation, cinematography, electromagnetically inductive and photoconductive transducers, and, most recently, radionuclide tracking. (Bates, J,F., 1975, Hannam, A.G., 1979)

During normal movements, the translations and rotations which accompany jaw motion are so complex that only those systems capable of expressing information with 6 degrees of freedom are properly able to measure displacement patterns at a given point. (Gillings 1973, Goodson 1975, Lemmer 1976) Although such devices exist, (Gibbs 1971, Suit 1976) most studies have been carried out with techniques involving two or three degrees of freedom and they have been confined to the description of incisor point movement only. (Bates 1975, Hannam 1979) Reasons for the acceptance of limited expressions of motion probably include the relative noninvasiveness of incisor point movement, the physical ease of the technique, its applicability to large numbers of subjects, the restriction of data to manageable proportions, and not least, the general lack of alternative instrumentation with desirable properties.

Several investigators have used the Kinesiography to monitor three- dimensional linear movement of an incisor point on the mandible. (Jankelson 1975, Morimoto 1977, Hannam, Scott, et al., 1977, Hannam, De Cou, et al., 1977) Apart from major theoretical limitations as outlined, the instrument offers properties which should be taken into account whenever quantitative measurement is contemplated. This article describes how they can be controlled in an experimental environment.

METHODS

The Kinesiograph basically consists of a set of magnetometers which sense the displacement, in three planes, of a small magnet cemented to the lower anterior teeth. These sensors are carried on a light framework supported by a spectacle-like device which is worn by the patient in a conventional fashion and stabilized with an elastic strip behind the head. The framework is arranged about the magnet in a prescribed way and usually zeroed to the intercuspal position of the patient before any recordings are carried out. The fundamental signals derived from the device are three voltages representing vertical, lateral, and anteroposterior jaw movement, respectively. The voltages are referenced to the planes of orientation of the magnetometers. This system is described in more detail elsewhere. (Jankelson 1975)

During bench tests, we have found the instrument to be a stable indicator of the position of the magnet provided the latter is not rotated. It responds acceptably to frequencies of displacement up to 150 Hz.

Aside from these limitations, two other aspects of the instrument‟s performance are notable. These are its inherent nonlinearity over certain prescribed ranges of linear displacement and the question of its orientation relative to craniofacial landmarks. Our observations concerning the management of both aspects are based upon experience with the earlier, K2 version of the Kinesiograph. The principles involved, however, can be applied equally to later versions of the instrument.

NONLINEARITY

The position of the magnet relative to the sensors on the framework of the kinesiograph determines the nature of the nonlinearity. If the magnet-to-frame relationship during set-up is as the manufacturers suggest, distortions are least near the intercuspal position (the zero point) and greatest at the more extreme positions, for example, near maximum opening or maximum lateral excursions.

Because any correcting operation has its greatest source of error where the distortion is most marked, it is prudent to first determine the range of movement anticipated under operational conditions and then to choose a set-up zeroed position of magnet-to-frame which is best able to distribute the nonlinearity as evenly as possible over the user‟s intended range. If, as in many cases, the entire range of the masticatory cycle is to be included, we have found it better to set the magnet 1 cm higher than suggested by the manufacturers. This not only serves to improve the distribution of the distortion but •has the practical benefit of permitting added clearance between the chin and the lower sensor.

Positioning the framework is approximate at best. The method nevertheless ensures that consequent errors are at least minimized. In a previous experiment, (Hannam, Scott, et al., 1977) we have use4 it repeatedly (15 times over 3 days) to remeasure a standardized jaw position in the same subject. The mean coordinates of this fixed point were estimated to be 19.3 mm SD + 0.4 vertical, 3.2 mm SD + 0.8 mm lateral, and 3.5 mm SD + 1.3 mm anteroposterior (n = 15), the variances expressing errors due to frame placement alone.

We believe that it may be possible to reduce errors in day-to-day measurement still further by referencing the framework to the maxillary dental arch. Before each recording session, a bite-fork registration of the arch can be made with conventional face-bow apparatus. At the end of the session, but before the Kinesiograph framework is removed, the bite-fork record is reinserted and held rigidly by the subject. The hinge-axis and orbital indicators are then reversed and aligned so as to signify coplanar points on the two lateral and single vertical sensors of the Kinesiograph. On its removal, this modified face-bow record indirectly provides a measure of the angular relationship between the actual reference planes of the Kinesiograph during the recording session and the conventional reference planes of semiadjustable or fully adjustable articulators.
The maxillary dental arch provides the common reference for relating one data set to the other: therefore, any simple measuring device can be used to estimate angular relationships between the two sets of planes.

DISCUSSION

More efficient, and perhaps more accurate, methods for linearizing and referencing the system may be possible than those described here. Whether these are worth pursuing depends upon the user‟s needs. In terms of bench performance with a linear calibrator, the instrument can resolve small changes in displacement, and it is theoretically possible, following suitable filtering procedures, to devise very accurate linearizing procedures under these conditions. These efforts, however, must be balanced against the fixed limitations inherent in the overall system, which produce errors that are difficult or impossible to control under functional conditions. Rotations at or around the incisal point cannot be measured, while the process of physical orientation and fixation of the apparatus is at best an imprecise exercise.

However, once the decision is made to accept the instruments restriction to expressing linear but not rotational motion of a single incisor point, the remaining limitations of the Kinesiograph can clearly be minimized to an extent that permits acceptable errors of measurement for many tasks. Such procedures may be entirely unnecessary if the system is only used to display jaw movements in a qualitative way. On the other hand, if comparative measurements are to be performed on a day-to-day basis, especially outside the intercuspal area, then additional techniques of this kind are obviously essential.

Although the suggested principle of zeroing the system to the intercuspal position seems to be satisfactory for most purposes, the alterations to this area which occur as a consequence of occlusal or orthognathic reconstruction frequently require the zeroed position to be related to more fixed, conventional, mandibulomaxillary references such as centric relation. This is especially true when there is a ambiguity in the intercuspal position, for example, in patients with excessive occlusal wear, or with “freeway in centric relation.” In this regard, it should be added that external manipulation of the mandible when the framework is in place can be difficult.

Several points have been mentioned which are not peculiar to the Kinesiograph alone. Any system used for measuring jaw movement should be recalibrated at regular intervals and under conditions resembling the actual recording environment as closely as possible. Identifiable planes of reference must be used and some kind of estimation made of the errors associated with placing the transducers on the subject. Finally, any system, whether it records the displacement of one or several points on the mandible in more than one dimension, creates a formidable problem in data management and its expression. Under these circumstances, digital conversion becomes an almost essential part of the process whenever quantitative measurement is contemplated.

CONCLUSIONS

Whenever the Kinesiograph is used to measure functional jaw movement, three factors should be taken into account. The instrument is theoretically limited by its expression of data with only 3 degrees of freedom of measurement, it has nonlinear response characteristics over the entire range of functional jaw movement, and it requires referencing to fixed craniofacial landmarks. Although the first limitation is inherent in its design and cannot be altered, the remaining two can be controlled sufficiently to permit the day-to-day expression with an acceptable error of measurement of linear incisor movement.

STUDIES THAT DOCUMENT VARIATION IN MANDIBULAR FUNCTION IN NORMAL VERSUS ABNORMAL POPULATIONS

Maruyama, et al, in a controlled study utilizing the Mandibular Kinesiograph and 70 subjects with normal occlusion quantitated the displacement between centric relation and centric occlusion. None of the 70 subjects showed coincidence of centric relation and centric occlusion. The expression of three dimensional deviation with the Mandibular Kinesiograph was a significant improvement over previous methods using one dimensional measurements to evaluate normal and physiologic relationships between maxilla and mandible.

Maruyama, T., Miyauchi, S., Umekoji, E., and Simoosa, T. Ana1ysis of the relationship of centric relation and centric occlusion by the Mandibular Kinesiograph. J. Osaka Univ. Dent. Sch. Vol 20, 173-178, 1980.

ABSTRACT

Three-dimensional relationship between centric relation and centric occlusion in human normal occlusion was analysed by using the Mandibular Kinesiograph, in order to know the normal and physiological relationship between maxilla and mandible in occlusal equilibration, occlusal reconstruction or oral rehabilitation.

The mean distance and standard deviation between centric relation and centric occlusion of anteroposterior, supero-inferior, right lateral, left lateral and linear directions at the mandibular incisor were 1.30. mm (S.D. 0.91 mm), 0.75 mm (S.D. 0.54 mm), 0.29 mm (S.D. 0.30 mm), 0.38 mm (S.D. 0.29 mm) and 1.53 mm (S.D. 0.81 mm), respectively. All the subjects showed anteroposterior deviation, most of the subjects showed superoinferior deviation.

MATERIALS AND METHODS

The subjects in the study consisted of 70 individuals (26 women and 44 men) between the ages of 23 and 35 years. All subjects had normal occlusion and no poor restorations and no complaints relative to the temporomandibular joints or masticatory muscles.

The magnet was positioned on the labial surfaces of the mandibular incisors and gingiva using the Myo-print resin (Myotronics Inc., Seattle Washington) horizontally in the vestible with the “N” towards the patient‟s left. The magnet was centered on the mandibular incisors with its long axis parallel to the plane of occlusion.

The sensor array was placed and adjusted as follows: a) Rotational adjustment; the central struct of the array was positioned perpendicular to the floor. b) Anteroposterior adjustment; the array was moved anteriorly or posteriorly until the magnet was centered between the lateral sensors. c) Vertical and lateral adjustment: the array was moved up or down until the magnet was centered vertically on the midline.

The recording procedures of centric relation and centric occlusion were as follows: a) The subject was asked to open and close for several times with his jaw pull back as far as possible until a light contact of the teeth was obtained. If the subject could not pull back his jaw by himself, the operator applied his hand to support the subject‟s jaw and help to open and close in centric relation. This recording was terminal hinge closure and centric relation contacts. b) Then, the subject was asked to open and close into maximum intercuspal position for several times. This recording was habitual closure and centric occlusion contacts. c) The sagittal and frontal recordings of centric relation and centric occlusion on the oscilloscope were photographed by the Polaroid camera.

DISCUSSION

Various investigations concerning the mandibular displacement between centric relation and centric occlusion have been performed. Posselt (1952) reported that 88% of 50 dental students could displace their mandibles posterior to the occlusal position. He showed that the mandible at the lower incisors moved posteriorly 1.25 mm+1.0 mm, and caudally 0.9 mm+0.75 mm from the intercuspal position using cephalometric roentgenogram. Kydd and Sander (1961) reported 100% of 14 subjects could show the posterior movement with the mean of 0.87 mm+1,00 mm, using serial roentgenograms. Ingervall (1964) reported all of 29% subjects showed the mean difference of 0.85 mm+0.35 mm between centric relation and centric occlusion. Remien and Ash (1974) reported the difference with the mean of 0.75 mm between centric relation and centric occlusion recorded by contact of the pin to the table of the Hight Tracer attached to the patient‟s mouth with clutches, and reported the difference ranging from 1.5 mm to 3.5 mm, with the mean of 2.2mm.

In our study, the means and S.D.s of the distance of anteroposterior, superoinferior, right, left and linear direction between centric occlusion and centric relation were 1.30 mm (0.91 mm), 0.75 mm (0.54 mm), 0.29 mm (0.30 mm), 0.38 mm (0.29 mm) and 1.53 mm (0.81), respectively. The means of the distance of anteroposterior and linear direction were slightly larger than the data reported by some of other investigators. It was because of the following reason. As the measuring point in this study was on the labial surfaces of the mandibular incisors and gingiva, the distance from the condyle was longer than other methods. If the deviation between centric relation and centric occlusion was one-dimensional, the position of the measuring point did not effect on the value of the measurements. But, as the deviation was three-dimensional, the value of the measurements became larger, when the measuring point was away from the condyle.

From the results that none of 70 subjects showed the coincidence of centric relation and centric occlusion in anteroposterior direction, the existence of the small distance or freedom between centric relation and centric occlusion in anteroposterior direction might be physiological phenomenon for an optimum occlusion.

McCall, et al, recorded jaw movement using a Hall-effect generator and a magnet attached to the lower incisors. Using computer programs, the authors established a mathematical model to reference the experimental data. Large model/experimental discrepancy was indicative of dysfunction with predictive success via accepted occlusal therapy. The study concluded that phase plane modeling provides quantitative measurement of joint dysfunction useful for monitoring treatment progress and identifying those cases which will respond favorably to occlusal therapy.

McCall, W.D., Jr., Bailey, J.O., Jr., and Ash, M.M., Jr. A quantitative measure of mandibular joint dysfunction: Phase plane modelling of jaw movement in man. Archs Oral Biol Vol 21, pp 685 – 689. Pergamon Press 1976. Printed in Great Britain.

METHODS

TRANSDUCER
Jaw motion was registered by cementing a small permanent magnet on a mandibular incisor and recording its magnetic field at a maxillary incisor with a magnetic field-sensing device (Kydd, Harrold and Smith, 1967; Bando et al., 1972; Woltjen et al., 1973; Jankelson et al., 1975). The device was a Hall-effect generator (Model HI-5, American Aerospace Controls, Farmington, N.Y.). It was sensitive to the static magnetic field and was not influenced by saliva, tongue, food bolus etc. in the intervening space. The output of thea+43Hgenerator was amplified and stored on analogue magnetic tape as part of a larger series of experiments. Typical raw data, including concurrent electromyographic (EMG) traces which will not be discussed here, are given in Fig. 1.

DATA PROCESSING

The term “phase plane arose in the study of non-linear differential equations and their engineering applications (Hsu and Meyer, 1968). There, the term denotes a plot of any dependent variable vs. its time derivative. Here, phase plane refers specifically to the plot of jaw position vs. jaw velocity

MATERIAL

The data from 9 clinically normal subjects and from 13 patients clinically diagnosed as having masticatory dysfunction were analyzed. Of the 13, 9 were responsive to treatment. The other 4 patients were refractory to treatment.

RESULTS

A typical phase-plane trajectory (a plot of jaw closing velocity vs. jaw position) from a normal subject started at an open jaw position and zero velocity (Fig. 3). As the distance decreased toward closing, the magnitude of the velocity increased smoothly to a maximum, and then rapidly decreased to zero at tooth contact. The rms error in normal subjects ranged from 10.5 to 18.7 per cent.

A typical phase plane trajectory from a dysfunctional patient prior to treatment by an occlusal splint showed large alterations of the velocity during closing (Fig. 4A).
After successful splint treatment, the amplitude of the velocity excursions was markedly attenuated compared to the pre-treatment trajectories (Fig. 4B). The error ranged from 7 to 17.5 per cent for successfully treated patients. The criterion for successful treatment was cessation of symptoms for a period of at least one month; these patients were then considered to be clinically normal.

Histogram of the rms error between the parabolic model and the experimental data (Fig. 5) showed that normal subjects and successfully treated patients fell, without exception, in the range of less than 20 per cent. The dysfunctional patients who were subsequently treated successfully by an occlusal splint showed, with one exception, a phase plane error at the pretreatment recording session which exceeded 20 per cent.

There were four exceptions to the general finding that patients with symptoms exceeded 20 per cent error and asymptomatic patients showed less than 20 per cent error. These patients were clinically diagnosed as having masticatory dysfunction but showed rms errors that would place them in the normal range of the histogram. The dysfunctional patients with large rms errors showed cessation of symptoms within a few weeks or even days with splint therapy; however, the four with small initial rms errors were refractory to the splint treatment for several months. Thus, by the method we report, it is possible to separate the dysfunctional patients into two groups; those who can be successfully treated and those who cannot be successfully treated by occlusal splint therapy alone.

DISCUSSION CLINICAL

It should be stressed that the idea of an “ideal” patient fitting an “ideal” parabola was not intended; the parabola was used only for convenience. There is no rational basis for attaching any clinical significance to the parabolic shape.

The mechanism which caused the velocity alterations in the dysfunctional patients is of great interest as it might provide some insight into the aetiology of the individual problem. The possible mechanisms include mechanical impediment in the joint or its capsular structures, alteration of muscular activity and peculiarity in the transducer system. Each may be excluded by the appropriate experiments: The contention that the velocity alterations arose wholly within the transducer system can be rejected because the device was monotonic in static calibration and had no dynamic properties to cause such a phenomenon. Moreover, normal subjects exhibited smooth velocity increases and dysfunctional patients who had been successfully treated exhibited markedly attenuated velocity alterations.

Alterations in muscle activity would be observed in the simultaneous electromyographic tracings if techniques were developed to correlate the EMG with the jaw motion traces.
We have not done so yet.

Regarding impediment in the joint itself, the possibility exists that the mechanisms causing clicking and crepitation are responsible for the velocity alterations on a purely mechanical basis.

Given previous separation by clinical examination into symptomatic and asymptomatic groups, the jaw motion technique we report here may provide a further separation of the symptomatic patients into two groups: Those who can and those who cannot be successfully treated by an occlusal splint. The phase plane method may also provide a quantitative method for monitoring the treatment progress of those dysfunctional patients who are responsive to occlusal techniques. It provides objective evidence, to support the subjective report of the patient, that the treatment has been successful.

Griffin, at the University of Sidney, recorded three dimensional mandibular movement using a mechanical mandibular kinematograph. Griffin concluded that jaw tracking evidence showed beyond reasonable doubt that TMJ dysfunction and its sequellae are related to mandibular displacement and that masticatory muscle asynergy in dysfunction is identifiable in variations of mandibular movement. The value of tracking mandibular relationships in assessing the status of the masticatory mechanisms is emphasized by the author.

Griffin, C.J. ―Diagnosis and treatment of mandibular displacements by mandibular kinematography. The dental nociceptive reflex.‖ Australian Dental Journal. pp 384-392, Oct. 1963.

Opening and closing the jaws to and from centric occlusion is ideally achieved by paired symmetrical muscles acting synergistically. This synergy of the masticatory muscles is depicted kinematographically as smooth strokes; on the other hand, asynergism is depicted kinematographically as abrupt horizontal or obliquely horizontal strokes. When asynergy is observed it must be considered pathological. Kinematographic evidence suggests that the muscles responsible for this asynergism are usually the lateral pterygoids and their antogonists the posterior horizontal fibres of the temporal muscles. The muscles most susceptible to trauma in strained temporocondylar relationships are the lateral pterygoids and pressure on their tendinous insertions into the meniscus and pterygoid fovea, by virtue of the Golgi tendon organs, would cause their inhibition and excitation of their antogonists. Inhibition of say the right pterygoid muscle would be seen kinematographically as a deviating left stroke during the initial opening movement of the mandible. This is because failure of its contracture prevents medial forward translation of the right condyle, hinge movement however being permissible. At a certain part of the opening movement the involved muscle is freed of pressure, it then contracts suddenly causing a right horizontal or right obliquely horizontal kinematographic stroke depicting an abrupt left deviating movement of the mandible. This is usually associated with strepitus menisci. (Griffin 1962) The mandible on closing is brought back into the displaced position by the elevators, predominantly excessive contraction of the posterior horizontal fibres of the right temporal muscle. It can be stated that asynergy is the result of untreated mandibular displacements and constitutes temporomandibular joint arthritis. When F.C.M. K.’s are taken a left traverse of the panel augments a right kinematographic stroke and a right traverse of the panel augments a left kinematographic stroke.

MANDIBULAR DISPLACEMENT

Mandibular displacements of any type must be considered as potentially pathological and as playing a factor in the aetiology of periodontal disease. Prior to orthodontic treatment they ought to be assessed and therapy planned in such a way that it does not counteract against the predominant muscle play. Similarly occlusal equilibration techniques ought to be planned in accordance with the existing maxillo-mandibular relationships. Mandibular displacements may be diagnosed kinematographically as follows:

1. A posterior displacement of the mandible is diagnosed by the fact that the terminal closing movement to the tooth position is posterosuperior.

2. An anterior displacement is diagnosed by the fact that the terminal closing movement to the tooth position is excessively anterior and that the kinematographic stroke depicting this movement is excessively obliquely horizontal. Usually the amplitudes of the kinematograms are excessive.

3. A lateral displacement is diagnosed by a left divergent or right divergent kinematographic stroke depicting the terminal closing movement to the tooth position.

4. A combination of these displacements is diagnosed by comparing F.M.K.’s with L.M.K.’s. They may be classified as follows: (i) A left postero-lateral displacement; (ii) a right postero-lateral displacement; (iii) a left antero-lateral displacement; (iv) a right antero-lateral displacement.

5. A compensated mandibular displacement is diagnosed by the synergy of the compensatory muscle movements. That is by smooth compensatory kinematographic strokes depicting the closing compensatory mandibular movement. In a compensated mandibular displacement the stroke depicting the opening movement of the mandible is usually nearly vertical, whereas the closing stroke diverges right or left as the mandible closes to the tooth position. This is because the D.N.R. corrects the displacement as far as the mandibular depressors are concerned.

6. An uncompensated mandibular displacement is diagnosed by the asynergy of the mandibular depressors, and is usually associated with strepitus menisci. This is because the D.N.R. is inhibited. Whereas synergistic mandibular displacements ought to be considered as potentially pathological, asynergistic mandibular displacements especially when the mandibular depressors are involved must be considered as definitely pathological. In this instance a diagnosis of temporomandibular joint arthritis is justifiable.

7. Kinematographic evidence suggests that the D.N.R. is only fully disclosed when there has been a considerable loss of vertical dimension, or when by reason of malocclusion there is a considerable contact pathway from contact to maximum contact. The vertical distance of the apex of this reflex above the clench line usually indicates the amount of space utilizable in oral rehabilitation. However, in temporomandibular joint dysfunction the reflex cannot usually be elicited, not even the reflex artefact. This is indicative of inhibition of the mandibular depressors.

8. Reflex incoordination may sometimes be assessed on the basis of patients ability to keep the head still during exercises. Most patients have no difficulty but patients with T.M.J. disturbances usually find it impossible to keep their heads still during recordings.

DISCUSSION

One of the features of the symptomatology of mandibular displacements is the fact that they symptoms either appear to be predominantly local or predominantly reflex in nature. They all, however, have one feature in common, asynergy of the masticatory muscles, the objective evidence of which can be seen kinematographically. Atkinson and Shepherd (Atkinson 1961) have previously presented evidence of muscular incoordination in T.M.J. dysfunction and have recorded it kinematographically.

Electromyographic evidence of abnormal muscular activity in these conditions has also been reported. Moreover it has been known for a long time that deviations of the mandible in opening and closing from and to the tooth position are signs of T.M.J. dysfunction. However, kinematographic evidence shows beyond reasonable doubt that T.M.J. dysfunction and its sequalae, reflex or local, are due to untreated mandibular displacements. It further indicates that muscular tensions are not per se the cause of these conditions, but may however precipitate them, in other words cause a potentially pathological condition to become pathological. Unfortunately mandibular displacements are often perpetuated in the edentulous patient and the resultant physical and psychological damage cannot be overestimated. Mandibular kinematography is an adjunct in the detection of these conditions prior to breakdown. It is also valuable in that the graphs indicate the method of treatment and check the success of treatment. It should be of value in all phases of dentistry because by it mandibular maxillary relationships may be assessed an the state of the masticatory proprioceptive mechanisms evaluated.

It would seem that maintenance of intact masticatory proprioceptive mechanisms is of supreme importance to the organism since the mesancephalic nucleus of the fifth nerve is anatomically dominant over other skeletal proprioceptive mechanisms. Its connections with cranial motor nuclei are direct and its connections with the reticular formation of the medulla and mesencephalon (Griffin 1962) indicate that disturbances of this nucleus can affect other remote reflexes (King 1955). Neurovascular and proprioceptive reflexes are intimately related and interdependent and it is hard to conceive one acting without the other. The exquisite coordination of muscular and vascular mechanisms indicates an extreme delicacy of the neural apparatus subserving its requirements and a disturbance of this system by unwarranted inputs from a disturbed masticatory system at a mesencephalic level may have far-reaching and untoward effects upon the organism.

Mongini studied masticatory function in 8 subjects with good function and 8 subjects with dysfunction. He found statistically significant differences between mandibular movements in the normal versus abnormal group.

Mongini, F. A graphic and statistical analysis of the chewing movements in function and dysfunction. The J. of Cranio. Pract. Vol 2, No. 2, March-May 1984.

ABSTRACT

To study the statistical differences between functional an dysfunctional chewing, the authors selected two groups of 8 subjects each. Group 1 consisted of subjects who had good masticatory function, while Group 2 was made up of subjects with dysfunction of the stomatognathic system. Each of the subjects was given the same amount of crispy bread and was asked to chew it normally. The subjects mandibular movements were recorded with an Electrognathograph which was connected to an XY chart recorder and a computer. The software produced date of the mean mandibular displacement on the frontal and the sagittal planes at 20 different degrees of jaw separation. Information on standard deviation values (i.e., the repetition or variability of movements) and on velocity was also obtained. Statistically significant differences were found between the movements of Group 1 and Group 2, which allowed the authors to assess some of the parameters typical of functional chewing.

RESEARCH

In recent years, chewing movements have been investigated by several different authors. They have used methods such as cineradiography (Modica 1968, Modica 1969, Hedegard 1970), photoelectric devices or light-emitting diodes (Gillings 1967, Gillings 1973, Waysenson 1977, Karlsson 1977, Jemt 1979, Graf 1982), implanted radionucleotides (Salomon 1979), and many others. Some investigations have used a sophisticated device that allows mandibular movements to be precisely recorded on tape. These can then be processed by a computer and reproduced on mandibular casts by means of a slow-speed playback device (Gibbs 1966, Gibbs 1969, Gibbs 1971, Gibbs 1982).

For this reason, we developed a computer-based system that was used to study both normal subjects and patients with dysfunction of the stomatognathic system. The purpose of this article is to describe the methods we used and to discuss the results obtained in our study.

RESULTS

The chewing movements of the subjects with good function (Group 1) showed a typical pattern when viewed on the chart recorder. On the frontal plane, the most extreme movements defined a symmetrical shape. We found this was true even when the subject had a preferred side for mastication; in such cases, although most chewing movements occurred only on one side, some symmetrical chewing strokes occurred on the opposite side as well.

DISCUSSION

The data at hand provided us with a good basis for assessing the statistical significance of the chewing movements of subjects with good function as well as of those with dysfunction of the stomatognathic system. We found the following patterns to be typical for functional chewing:

1. The opening movement tracks a rather repetitive path that shows little displacement from the mid-sagittal plane and runs parallel to it.

2. The closing stroke is concave towards the mid-sagittal plane, and the maximum skid is reached in the middle third of the path, usually just before the halfpoint is reached. This closing stroke is fairly variable, and movements become gradually less extended while the bolus is being chewed.

3. Even with subjects who have a preferred mastication side, closing movements occur on both sides, and they tend to be symmetrical.

4. On the sagittal plane, both opening and closing movements are fairly repetitive. Posterior displacement increases as the degree of jaw separation increases, and the closing stroke is located posterior to the opening movement. Anterior displacement rarely occurs, and then only at a small degree of jaw separation.

5. The velocity is high, with maximum values occurring in the middle third of the opening movement and in the first half of the closing movement.

Single figures can obviously vary considerably among the different nondysfunction subjects, but the similarity of the patterns that are presented is suggestive of standard movements.

However, when the data gathered from several dysfunction patients are compared, we can see that the differences between these subjects are striking. The patterns that we have just described as typical for good function are altered or even absent in these patients. We can assume with reasonable certainty that the number of patterns considered normal decreases as the degree of dysfunction increases. However, further investigations are needed to confirm this idea.

Ow, et al, used optoelectric tracking to analyze jaw movement in six subjects before and after treatment for craniomandibular disorders. Findings showed significant changes in velocity and duration of the chewing stroke after treatment. The authors conclude that increase in chewing rhythmicity was correlated to decrease in patient symptoms.
Ow, R.K.K., Carlsson, G.E., and Jemt, T. Craniomandibular disorders and masticatory mandibular movements. J. of Craniomandib. Disord.: Facial & Oral Pain. 1988; Vol 2, No. 2:96-100.

A subgroup of six women aged 21 to 39 years were studied for their responses to treatment for craniomandibular disorders of neuromuscular origin. Severe clinical symptoms were ameliorated over a 5- to 8-week period. A standardized recording of their chewing movements in response to treatment was done with an optoelectronic measuring system. Comparison of chewing cycle variables, before treatment began, with those obtained after the 5- to 8-week period of treatment showed that changes in speed and duration of the opening stroke in comminution were indirect indicators of recovery from dysfunctional symptoms in the masticatory system. These two parameters effected a significant change in the overall rhythmicity of chewing for these subjects.(J CranioMandib Disord 1988;2:96-100).

The purpose of this study was to determine if the results of conservative treatment for a selected subgroup of patients with CMD of neuromuscular origin (or myofascial pain-dysfunction syndrome) could be shown to influence their chewing cycle pattern.

Statistical Analysis: Analysis, by using the paired t test, was performed for the group of subjects. Statistically significant differences were highlighted and the level used was P < 0.05. If P > 0.05, the difference was designated NS (not significant). The coefficient of variation (CV) was used as a measure to describe the amount of variation in the sample.

RESULTS

Chewing Variables- -Rhythm, Speed, Displacement, and Area. The overall duration of a chewing cycle (rhythm) comprised an opening phase, a closing phase, and an occlusal phase. For the six subjects, the opening phase was significantly shortened from 0.18 seconds to 0.17 seconds (P < 0.05). The overall cycle duration (rhythm) was also reduced significantly from 0.55 seconds to 0.52 seconds (P < 0.05). The closing phase and occlusal phase of the chewing cycles recorded no significant changes.
The mean opening speed of the mandible in chewing was increased significantly from 65.35 mm/s to 73.45 mm/s (P = 0.05) after the 5- to 8-week period of treatment. The mean closing speed and the maximum speed of the mandible showed higher values, but these were not significant.

Mandibular displacement in chewing was reflected by the length of the opening stroke, the length of the closing stroke, the maximum lateral distance, the maximum vertical distance in a cycle, and the amplitude (square root of the sum of the squares of the maximum lateral and vertical cycle distances). Mandibular displacements were seen to increase, but not significantly.

The enclosed area of the chewing cycle was measured in the frontal plane, the sagittal plane and the horizontal plane. There were not significant results shown, but the frontal and sagittal loop areas increased.

DISCUSSION

The subgroup of six women, aged 21 years to 39 years, corresponded to the clinical material of CMD seen in most studies. (Mejersjo 1983, Dahlstrom 1982, Magnusson 1978) They responded fairly well to conservative treatment over the period of 5 to 8 weeks. Both signs and symptoms of CMD were ameliorated, and the frequency of headaches diminished.

The tenderness of the masticatory muscles on palpation was reduced in intensity and location with treatment. Other symptoms were mandibular deviation in opening, tenderness over the temporomandibular joint area, and movements of the mandible that were associated with pain. These latter symptoms abated at the 5- to 8-week period of treatment.

The overall duration of the chewing cycle of the six subjects was significantly shortened. The opening phase of the chew was also slightly but significantly shortened. These were interpreted as responses in the chewing cycle to the interim effects of treatment of muscular dysfunction. Other studies (Atkinson 1961, Stohler 1985) have shown irregularities in chewing rhythm for patients with similar disorders, but did not show how these were affected by treatment. The opening speed of the mandible after treatment was significantly increased for the six subjects. It appears reasonable to deduce that changes to the speed and the duration of the opening stroke have significantly affected the overall duration or rhythm of comminution.

The lateral pterygoid muscles, particularly their inferior head, and the fibers of the digastric muscles are known to be active in opening mandibular movements. (Wood 1987) It is believed that their main action is in ballistic mandibular opening. (Jemt 1984, Carlsoo 1956, Ahlgren 1966) The effects of muscular dysfunction and of treatment could perhaps be seen more clearly in the opening movement of the mandible, since muscle activity is not apparently complicated by antagonistic muscle control. (Jemt 1984, Wood 1987).

Recovery of subjects having pain and dysfunction of the masticatory system could be seen when masticatory muscle hyperactivity was effectively controlled by appropriate treatment. (Thomson, H., 1975, Mejersjo 1984, Kopp 1979, Dahlstrom 1985, Carlsson 1985) An increased overall cycle rhythm could indirectly indicate a return to normal tonicity and smooth reciprocal activity of the muscles that govern mandibular movements. The results of our study verify that successful treatment not only reduces pain and dysfunction, but also leads to a normalization of masticatory function.

STUDIES THAT DOCUMENT THE CLINICAL EFFICACY AND VALIDITY OF MANDIBULAR TRACKING

Jankelson systematically describes the rationale and protocol for using mandibular tracking for diagnosis and treatment of orthodontic patients. The use of mandibular tracking as an adjunct to cephalometrics for orthopedically aligning the mandible to the cranium is a valuable objective quantitative technique.

Jankelson, B. Three dimensional orthodontic diagnosis and treatment a neuromuscular approach. J. of Clinical Orthodontics. Vol. XVIII, No. 9, Sept. 1984.

The use of electronically derived measurements and objective, quantitative data to diagnose the functional status of the musculoskeletal system of the head and neck is a significant step forward in the evolution of orthodontics into a major orthopedic specialty.

Musculoskeletal dysfunction of the head and neck is often the primary etiology of a diverse group of symptoms such as TMJ dysfunction, headaches, myalgia, otalgia, cervicalgia, and neuralgias. (Cooper and Rabuzzi, 1984; Jankelson, Dent Clinics 1979; Jankelson, mt Prosth Cong, Cluster‟ 1979; Jankelson, 1972; Principato, 1982; DeBaisi and Neironi, 1982; Dinham, 1970; Gernet et al, 1980; Vesanen and Vesanen, 1973; Weiss, 1976; Wessbert et al, 1981; Bazzoti, 1983; Choi and Mitani, 1973; Schwartz, 1955; Thompson, 1971; Carlsson, 1981; Reik and Hale, 1981; Farrar, 1979; Gelb et al, 1978; DeSteno, 1977; Laskin, 1969; Mikhail and Rosen, 1980; Burton, 1969). Before beginning treatment, the orthodontist should consider musculoskeletal dysfunction as a possible cause of one or more of these symptoms or as a presymptomatic potential for future dysfunction (Cooper and Rabuzzi, 1984; Jankelson, 1982). Today’s superior diagnostic capabilities can uncover and intercept presymptomatic musculoskeletal disease that could become acute and symptomatic under the added stress of orthodontic procedures.

Measurement for the diagnosis of existing musculoskeletal dysfunction in the orthodontic patient provides a needed additional functional diagnosis to complement the conventional use of cephalometric and TMJ x-rays. The electromyograph (EM2) and mandibular kinesiograph (MKG) respectively measure electrical activity of the muscles and the skeletal relation of the mandible to the skull. These data are essential for initial diagnosis, monitoring of treatment progress, and verification that a relaxed Neuromuscular environment- which is the goal of functional orthodontic treatment- -has been obtained for the finished case.

SUMMARY

Improvement of appearance is a primary motivation for patients seeking orthodontic treatment. However, every orthodontic patient is also a neuromuscular patient. Alleviation of the head and neck pain of musculoskeletal dysfunction must become an equally strong motivation for orthodontic care, as health-care professionals and the public become increasingly aware of its effectiveness and availability.

It is essential in the diagnosis of every patient, before instituting therapy, to derive precise, quantitative data that reveal whether the skeletal relation of the mandible to the skull is distorted or not, and document the extent of musculoskeletal dysfunction of the head and neck stemming from an existing malpositioned occlusion.

Structural diagnosis based on cephalometric and other x-rays gains in significance when supported by functional data of musculoskeletal status. The increasing emphasis on the orthopedic correction of skeletal malrelation of the mandible to the skull inevitably expands the scope and changes the image of orthodontic practice. As EMG and MKG data show, the significance of the orthopedic capability of orthodontics extends beyond the jaws along to the entire musculoskeletal system of the head and neck; and, as functional considerations become paramount, the orthodontist becomes the primary orthopedic specialist in treatment of head and neck pain.

Callendar discusses the rationale and protocol of integrating mandibular tracking into traditional diagnostic techniques. Pre and post treatment evaluation of orthodontic and TMJ problems utilizing mandibular tracking provides a more predictable, functional and stable result.

Callender, J.M. Orthodontic application of the Mandibular Kinesiograph: Part II. J. of Clinical Orthodontics, Vol XVIII, No. 11, pp 791-805, Nov. 1984.

CONCLUSION

This series of articles has introduced a concept of treating orthodontic cases in the vertical dimension to a determined rest-to-closure distance, with the occlusion set on a pathway on which the jaws are free to open and close without encumbrance and with relaxed musculature. This position is often at variance with existing dentric occlusion or with a centric relation achieved by the most distal positioning of the condyles. It is a stable post-treatment position, at which the condyles are well centered in the fossae.
This treatment does not discount current orthodontic concepts. It uses an additional diagnostic tool- -the MKG- -which allows visualization of the functioning jaws, and it cross-references this data with that of traditional orthodontic diagnostic techniques.

All the traditional orthodontic treatment modalities, along with the new concepts in functional appliances, are used to resolve functional problems. Functional appliances are fabricated to the jaw position indicated by the MKG. We have been able to create occlusions and jaw functions that are dramatically more freer of pathology-producing dysfunction, and that have remained free of dysfunction for a number of years. The MKG is also used post-treatment to assure that functional goals have been achieved. Continued evaluation of completed cases demonstrates that the MKG-dictated resolution of orthodontic problems and TMJ dysfunction is efficient, stable, and economically viable.

Callendar discusses the rationale and protocol of integrating mandibular tracking into traditional diagnostic techniques. Pre and post treatment evaluation of orthodontic and TMJ problems utilizing mandibular tracking provides a more predictable, functional and stable result.

Callender, J.M. Orthodontic application of the Mandibular Kinesiograph: Part L. J. of Clinical Orthodontics. Vol XVIII, No. 10, pp 710-718, Oct 1984.
In our office, in addition to standard orthodontic records and tomograms, we do a mandibular kinesiograph (MKG) analysis on patients who present any of the following symptoms:

* Joint noise or encumbered opening and closing of the jaws

* Pain to palpation of the joint capsule and several muscles of mastication

* Chronic ear problems

* Poor rate of opening and closing the jaws

* Diminished range of motion of the jaw (in three dimensions)

* Various crossbites or septal midline asymmetries

* Various tongue-swallow dysfunctions

* Various airway problems

* Apparent skeletal disproportions of the jaws

* Various facial asymmetries

PRETREATMENT FUNCTIONAL ANALYSIS

Pretreatment jaw function is analyzed by recording typical jaw motions on the cathoderay screen. To understand abnormal MKG tracings, it is necessary to know the appearance of normal tracings.

The greatest value of an MKG is that it gives the operator electronically magnified eyes to view the stomatognathic system in function. As the operator gains experience, he can develop hypotheses for resolving dysfunction and observe their validity live prior to pursuing irreversible treatment procedures.

INITIAL ANALYSIS

The initial analysis of jaw function is made using these photographs together with study casts and pantographic, cephalometric, and tomographic x-rays. Hypotheses can be tested by observing the screen as the patient performs various jaw functions- – swallow, speech sounds, maximum opening and closing, stretch reflex, etc. Plans must be made to eliminate contributors to abnormal jaw function.

We often find it necessary to use a splint to negate proprioceptive influences. Psychic input that is affecting jaw function can also be evaluated.

In my experience, very few young people have suffered pathologic alteration of the mandibular condyle, meniscus, or temporal fossa. It is common for them to have clicks and pops associated with entrapment of function of the joint parts. These alterations of joint function can be observed and measured on the MKG screen. They often can be correlated with abnormal positions of the condyle in the temporal fossa at centric or during translation of the joint as observed in tomograms. Their resolution should be planned during this analysis.

RECORDING MYOCENTRIC

After carefully analyzing all the factors involved, joint condition, swallow reflex, airway, occlusion, etc.the doctor marks a point on the screen where he wants the jaw to be positioned. A photograph of the screen is made at this point, which reflects the condition of the musculature and the quality of muscle function at the time of registration.

The technician then makes the acrylic index of that jaw position, and marks on the photograph the precise point at which the patient was directed during registration.
A point 1.5mm above physiologic rest is chosen to record the bite index. This is to be the eventual myocentric. The index is used for mounting one set of casts to be used during diagnosis. We routinely index within 0.25mm of our chosen point on the screen in all three planes of space. In cases of reciprocal click, it is extremely important that the point of index be on the path of closure at more jaw opening than the point of reciprocal click. We want to be sure the meniscus is recaptured by the condyle, and not displaced. This takes precedence over initially achieving myocentric, and it must be documented in the records to avoid confusion later on.

TREATMENT PLANNING

Information for treatment planning includes the patient’s history, range of motion, and muscle palpation charts that are completed at the initial examination. All x-rays, including tomograms of the joints are arranged for viewing on a large medical viewer so that they may be cross referenced. Two sets of models are used one set oriented to the existing occlusion in the traditional orthodontic manner, and the other mounted on a Galetti articulator, using the MKG indices.

The notes made while observing the patient on the MKG screen and the photographs of the screen are also important, because they document the initial problems and qualify the MKG indices. The initial MKG index does not always represent the myocentric that we are trying to achieve. Although it is taken with the jaws closing on the trajectory dictated by the relaxed musculature, there are sometimes vertical interferences such as division 2 anterior tooth interference, tongue volume, airway demands, and collapsed dental arches with complicated occlusal schemes. The intention is to plan initial treatment with the best jaw position possible.

We use any procedure needed to achieve an unencumbered path of opening and closing of the jaws as demonstrated on the MKG, and we are careful that we have achieved myocentric before final treatment is planned.

Once a trustworthy MKG index is achieved, final treatment planning is undertaken to resolve the orthopedic and orthodontic problems. The concept is to treat to an MKG-defined jaw position and not to an existing centric occlusion. Incipient pathology may already be present in the joints.

George and Boone used the MKG to study vertical dimension of rest position and mandibular closure to maximum intercuspation of the teeth. The many potentials for clinical use of the MKG for mandibular tracking are clearly brought forth.

The investigation also showed “that the Myo-monitor does relax musculature to a highly significant degree.” Again, the thesis that lowered postural activity is a desired biofeedback objective would validate the Myo-monitor as a modality contributing to the clinical objective. Therefore, if the preliminary committee draft statement “As a treatment tool, EMG has been and is being used in conjunction with relaxation and biofeedback therapy” is clinically valid, this controlled study documents the efficacy of the Myo-monitor to achieve the same physiologic result. To regard the relaxation tool of the dentist, i.e. Myo-monitor, as being not clinically acceptable while the tool of the psychologist is recognized is antithical to honest scientific inquiry. If relaxation is a valid clinical objective for biofeedback, it is a valid clinical objective for the dentist responsible for occlusal therapy.

George, J.P. and Boone, M.E. A clinical study of rest position using the Kinesiograph and Myo-monitor. The Journal of Prosthetic Dentistry. Vol. 41, No. 4, pp 456-462, April 1979.

However, rest position and closure through interocclusal distance represent a physiologic three-dimensional occurrence in space. The muscles involved are not just the elevators of the mandible. There are also the prime movers, the antagonists, and the synergistic muscles that help stabilize the movement. Muscle contraction also depends on the metabolic condition of the fibers, since contraction depends on the ability of the muscle tissue to use and resynthesize high-energy phosphate compounds in the presence of minerals, particularly calcium and magnesium. Proper nutrition and metabolic balance are necessary for the efficiency of this system (Anthony, C.P. and Kolthoff, N.C. 1975; Montgomery, R., Dryer, R.L., Conway, T.W., and Spector, A.A. 1977). Furthermore, numerous studies (Vig, P.S., and Hewitt, A.B. 1975; Mulick, J.F. 1965) have shown that skeletal facial asymmetry is prevalent in most persons, emphasizing the importance of measuring the three dimensions of the vertical dimension of rest position.
Until recently the instrumentation for three-dimensional measurements has not been available. This study was designed to show rest position and closure through the interocclusal distance in three-dimensions; and an electronic instrument, the mandibular Kinesiograph, was used (Jankelson, B., Swain, C.W., Crane, P.F., and Radke, J.C. 1975). The Kinesiograph is able to measure the mandible as it moves freely or during tooth contact in the frontal, sagittal, and horizontal planes simultaneously. The study was also designed to show rest position and closure before, during, and after muscle relaxation.

The Myo-monitor (Jankelson, B. 1969) was used to relax the musculature by a light myopulse induced electronically. The Myo-monitor was used because of the claim that it can relax musculature. Studies have shown that repeated electrical stimulation increases the potential of the electrical output of the muscles and that short, rhythmic muscle contractions enhance muscle blood flow and therefore nutritional enrichment (Dixon, H.H., O‟Hara, M., and Peterson, R.D. 1967; Selkurt, E.E. 1971).

The present investigation was designed to help the dentist visualize mandibular movement as three dimensional and appreciate the variability of the postural position as a necessary physiologic entity. The usefulness of measurement by the mandibular Kinesiograph and the effectiveness of the Myo-monitor as a muscle-relaxing tool will be described.

METHODS AND MATERIALS

The 14 subjects used in the study included four women and 10 men ranging from 21 to 50 years of age

RESULTS

Tracings and the points of measurement of the mandibular movement obtained from the Kinesiograph are shown in Figs. 3, 4 and 5. Measurements were made of the vertical dimension of rest position to closure into centric occlusion before, during, and after stimulation by the Myo-monitor.

Clinical data were analyzed for vertical, anteroposterior, and lateral components of movement using the factorial analysis of variance with repeat measures design (Winer, B.J. 1962). T-tests were used to determine the significance of movement in the lateral component. Differences between positions and between days for the vertical component of movement are recorded in Table I, which shows a significant difference between positions (F = 38.08, p < .001) regardless of the day the measurement was made.

The three positions over the three days were subjected to the Newman-Keuls sequential range test (Winer, B.J. 1962) for multiple comparisons. All pairwise comparisons were significant at the .01 probability level. Position 3 showed greater mean values than either position 1 or position 4. Position 1 showed the smallest mean value.
The data for the factorial analysis of variance between positions and days for the anteroposterior component of movement are shown in Table III. There was no significant difference between either days or positions. The F values for the anteroposterior component were the lowest of all those for the three movements.

Factorial analyses of variance on the data between positions and days for the lateral component of movement are shown in Table IV. There was no significant difference between either days or position. The F value between positions had the highest value, which was not considered significant since the probability level is between .05 and .10.
The data for the lateral component of movement were subjected to t-tests to detect the significance of lateral movement (Table V). No movement was assumed to be zero, so that t-tests statistically tested the presence of lateral movement. There was a difference at the .05 level in position 1 on all three days, in position 4 for the last two days, and in position 3 for the last day. An important finding was a consistent lateral component of movement prior to Myo-monitor stimulation.

DISCUSSION

The results of the investigation of vertical movements show that the Myomonitor does relax musculature to a highly significant degree. During the Myomonitor relaxation procedure, the facial muscles, along with the masticatory muscles, were subjected to myo-pulse exercise. This may have been the reason for the greater interocclusal distance. The finding of greater interocclusal distance during relaxation is consistent with Griffiths (1975) finding of increased interocclusal distance during sleep. Griffiths, who studied only vertical movement, attributed the increased distance partially to relaxation of the facial musculature.

In this study, regardless of differences in the vertical position within the rest position range, there were no significant differences in anteroposterior or lateral movements. These findings mean that the mandible dropped inferiorly in the resting range. This inferior movement means a changing of the rotational axis. Closure, then, would be around a changing axis. Since the mandible is suspended, it should be considered a definite possibility that the rotational axis does change during function.
An increase in vertical distance without significant anterior or posterior movements could be due to relaxation of the facial musculature, but it must be accompanied by or result in inferior movement of the mandible, not in movement which would describe an arc around a fixed condylar axis.

Results of the lateral component of movement showed that there was no significant difference in position before, during, or after relaxation procedures or between sittings. In previous studies of rest position the lateral component of movement has received scant attention, and no quantitative study is known to exist. For this reason, position No. 2, the myo-pulse movement, was also included in the statistical data, and the lateral component of movement was compared to zero movement by t-tests. Differences were found to be significant, particularly before relaxation. A review of the literature involving facial asymmetry shows that this should be no surprise. In a radiographic study of subjects with no clinical evidence of unacceptable facial asymmetry or gross deviation of dental arrangement, Vig and Hewitt agreed with earlier studies (Burke, P.H. 1971; Mulick, J.F. 1965) in reporting that there was an overall facial asymmetry. More study is needed to determine how this deviation relates to deviation on maximum opening.
If the rotational axis changes, a muscular adjustment would be expected prior to closure, which positions and alerts the musculature. As a supplement to this adjustment, or as a substitute for it, there may be a “directional adjustment” which serves as a guide to closure when tooth contact occurs. This adjustment would occur in all three planes.
Figs. 6 and 7 show this phenomenon, and it can be seen in most tracings. Muscle length may vary, depending upon the stress within the system, and variability of the vertical dimension of rest position seems necessary to accommodate tension or relaxation in the musculature; therefore the cuspal slopes of teeth may act as the final guide to closure. This interpretation is supported by Posselt‟s (1968) three-dimensional diagram of the envelope of motion, which shows maximum intercuspation to be the point of a pyramid.

A question arises as to the accuracy of the Kinesiographic representation of movement. The Kinesiograph has been reported to have an accuracy of 0.1 mm for the resolution of mandibular position in the vicinity of occlusion. At a vertical opening of 20 mm the geometric error is -3% in the vertical, +5.7% in the anteroposterior, and 0 in the lateral component. If at 20 mm of vertical opening the mandible is moved either to the left or to the right 10 mm, then a -6% error would occur in the lateral component, so that a 9.4 mm lateral reading would be shown on the cathode ray tube.

Since measurement in this study did not deviate from the null point of occlusion more than 5.5 mm, and since this was a comparative study, no effort was made to make a correction to absolute data. However, a computer program could be designed to accomplish this correction.

One other variable that could influence the accuracy of the study was head position of the subjects. No restrictive headrest was devised because of its possible effect on the relaxation of the musculature. However, head position was monitored visually. Head position could possibly be monitored electronically with the aid of a sensor that could detect variation from a predetermined position.

Patients devoid of neuromuscular symptoms were purposely selected to establish some norm for future studies. Future studies could include subjects with neuromuscular problems. The vertical dimension of rest position could also be studied with reference to centric relation in asymptomatic patients.

SUMMARY

This clinical study was designed to study the vertical dimension of rest position and mandibular closure to maximum intercuspation of the teeth before, during, and after relaxation procedures on 14 subjects with stable dentitions. The findings call attention to the potential of both the Myo-monitor and the Kinesiograph for research and clinical use, to the physiologic need for flexibility of the vertical dimension of rest position, and to the importance of measuring all three dimensions when examining the rest position.

Konchak, et al, evaluate before and after TENS mandibular position correlating SN/mandibular plane angle and clinical freeway space. The study concluded that the S-N/MP angle did not prove to be a reliable predictor of freeway space. However, the authors point out that both clinical rest position and physiologic rest position can be differentiated using the Myo-monitor and Mandibular Kinesiograph.

Konchak, P.A., Thomas, N.R., Lanigan, D.T., and Devon, R. Vertical dimension freeway space, a kinesiographic study. The Angle Orthodontist. pp 145-154. April 1987.
Fujii (1977) and Godaux and Desmedt (1975) demonstrated that transcutaneous stimulation produced deconditioning of musculature by reducing muscle spindle feedback. The proprioceptive disfacilitation following TENS has been explained by antidromic block via the fifth cranial nerve motor fibers (Hoffman 1918, Magladery 1955, Homma 1959), inhibition by upper motor neurons on the motor nucleus of the trigeminal nerve (Teasdall et al. 1952), and deactivation of the gamma motor neuron drive to the muscle spindles (Valibo 1971).

The muscle relaxation that results from TENS-induced proprioceptive disfacilitation of the fifth motor neurons is not a fatigue phenomenon, as is shown by the heightened masticatory muscle force following TENS, the elevated maximal velocity of jaw closure, and the increased integrated electromyographic activity of the masticatory musculature during clenching.

The proprioceptive disfacilitation is sustained as long as the teeth are not brought into occlusion and TENS is maintained (Jankelson and Radke 1978). Fujii (1977) has found that the proprioceptive disfacilitation is released at a slightly longer interval than 80-95msec, a time that is clearly not indicative of a fatigue phenomenon.
Wessberg (Wessberg and Epker 1981, 1983, Wessberg et al. 1981, 1982) has defined “clinical” and “physiological” rest positions of the mandible that appear to correspond to Jankelson‟s “adaptive” and “true” rest positions of the mandible. Rugh and Drago (1981) studied rest position and jaw muscle activity using EMG and the kinesiograph and reported that clinical rest position is accompanied by muscular activity. Yemm and Berry (1969) conclude that mandibular rest position is largely governed by an equilibrium of elastic forces when the subject is fully relaxed and muscle activity is not fundamental to the posture.

RESULTS

The subjects were arranged into the three groups in order of increasing SN/MP angle and the mean values for “adaptive” and “true” freeway spaces calculated (Table 1). Differences between the pre and post stimulation measurements were seen to both increase and decrease with respect to the adaptive freeway space measurement, although the mean difference for each group was seen to be positive (Fig. 3).

The overall mean “adaptive” and “true” freeway spaces for the 25 subjects in the study was 1,8 mm and 2.9 mm respectively. An analysis of variance to compare the “adaptive” and “true” freeway spaces of these subjects showed a significant increase in freeway space following transcutaneous electrical nerve stimulation (F(1,24)=7.625) (.01<P<.02).

This statistical test also revealed that subject variation was significant, indicating that not all subjects reacted in the same manner to the electrical stimulation (F(24,25)=2.64) (.01<P.<.02).

An analysis of variance was also performed to learn whether low (<25o) S-N/MP angle subjects behave differently from medium (25-38o) and high (>38o) S- N/MP angle subjects. The results demonstrate no significant variation among these groups, although the sample size of this study may be too small to detect some statistical differences.
Linear regressions were performed to determine whether there was any correlation between the S-N/MP angle and the “adaptive” and “true” freeway spaces. These demonstrated that there was a significant negative correlation between “adaptive” freeway space and S-N/MP, with 34.5% of the variation in freeway space being accounted for by the S-N/MP angle (r=O.587; slope=-3.34 and intercept=37.49 (Fig. 4).

The “true” freeway space, however, did not correlate with the S-N/MP angle, with only 1% of the variation in freeway space accounted for by total variation in the S-N/MP angle (r=0.1066; slope=-0.35 and intercept=32.31) (Fig. 5).

DISCUSSION

The desirability and validity of using freeway space measurements in dentistry has been widely debated. Silverman (1957) criticized principles and techniques based on rest position and freeway space as “the greatest single cause of so much confusion of maxillo-mandibular relations”. Atwood (1956) and Olsen (1951), using cephalometrics, showed that freeway space was not an accurate procedure. In their studies, measurements were made before and after loss of the dentition, with dentures in and out of the mouth, at the same and at different sittings. Freeway space measurement varied in the same patients.

One possible reason for this uncertainty is that the various clinicians and researchers are often discussing and evaluating two separate entities – physiologic and clinical rest position, without adequately differentiating between the two. The means for measuring these two positions was also inadequate until the use of the Myo-monitor and kinesiograph enabled clinicians to accurately measure both of these positions of the mandible (Jankelson and Radke 1978, Myotronics 1977, Hannam et al. 1977, Jankelson 1980). It is only recently that researchers have begun to use this sophisticated technology to investigate freeway space.

Wessberg et al (1982) found the interocclusal distance at physiologic rest position to be inversely related to the vertical dentofacial morphology.

In this study, the “adaptive” or clinical freeway space was significantly correlated with the sella-nasion/mandibular plane angle, whereas “true” or physiologic freeway space was not. Although there was an overall mean positive increase in freeway space of 1.1mm after TENS stimulation, it should be noted that differences between freeway space before and after stimulation could be either positive or negative. If relaxation of the muscles does occur (Jankelson 1982), it does not necessarily mean that freeway space values are larger after stimulation. Relaxation of the musculature is thus not necessarily synonymous with an increase in freeway space, as it could depend upon whether the elevator or depressor muscles have been relatively more relaxed

Freeway space is a description, however limited, of a physiologic parameter of an individual patient

Wessberg, et al, used the Mandibular Kinesiograph to determine mandibular rest position induced by phonetics, TENS and integrated EMG of the masticatory muscles. The authors found that these were three distinct biologic positions that are reproducible over time. They conclude that clinical rest position and physiologic rest position provide a scientific means of measuring neuromuscular adaptation.

Wessberg, G.A., Epker, B.N., and Elliott, A.C. Comparison of mandibular rest positions induced by phonetics, transcutaneous electrical stimulation, and masticatory electromyography. The Journal of Prosthetic Dentistry. Vol. 49, No. 1, pp. 100-105, January 1983.

RESULTS

A three-way analysis of variance with one observation per cell was performed to analyze the data obtained from this investigation. The factors analyzed were experiment, treatment, and subject. This analysis revealed no experiment-by-subject interaction (p = .24) and no experiment-by-treatment interaction (p = .51), but there was a significant subject-by-treatment interaction (p < .01). These interactions are illustrated in Figs. 5 to 7.

Neuman-Keuls multiple comparisons were performed at the .05 significance level for subjects and experiment and for subjects and treatment. These comparisons found no significant difference in mean response for subjects across experiment. These comparisons also showed that treatments PRPM-TES and PRPMEMG are not significantly different and that both yield higher mean responses (greater IOD) than the CRPM (phonetic) treatment.

DISCUSSION

The results of this investigation of mandibular rest position induced by phonetics, TENS, and integrated masticatory EMG in four adult women with normal dentofacial morphology were significant in several aspects. Primary among these findings is the fact that the three mandibular rest positions are biologically distinct entities that are reproducible across time. The data obtained in this study demonstrated the mean IOD at the CRPM (phonetics) to be 2.5 + 1.2 mm and at the PRPM to be 5.2 + 1.5 mm (TES) and 5.3 + 1.9 mm (EMG).

The second important feature of this investigation is the fact that PRPMs induced by TES and minimum integrated masticatory EMG were not statistically different. In essence the determination of the PRPM can be induced reproducibly by either TES or minimum integrated masticatory EMG activity.

The findings of this investigation are relevant to clinical research involving the stomatognathic system. The CRPM and PRPM may now be employed to measure the effects of prosthodontic, orthodontic, and orthognathic surgical procedures that significantly alter the occlusal vertical dimension. Specifically, pretreatment and posttreatment measurements of the CRPMs and PRPMs in individuals who undergo prosthodontic or orthodontic procedures that significantly “open the bite” (increase occlusal vertical dimension) or orthognathic surgical procedures that reposition the maxillae superiorly or inferiorly will reveal the subsequent neuromuscular adaptations that occur within the stomatognathic system.

SUMMARY AND CONCLUSION

Four adult women subjects with normal dentofacial morphology and a complete dentition were employed to compare the IOD at the mandibular rest positions induced by phonetics, TES, and minimum integrated masticatory EMG (treatments). A mandibular kinesiographic instrument that had been tested for reliability was used as a biologically compatible instrument for the measurement of the IOD at the four weekly experiments. A three-way analysis of variance and Neuman- Keuls multiple comparisons revealed that the three mandibular rest positions studied were reproducible within a specific subject at various time intervals. In addition, IOD at the CRPM (2.5 mm) was significantly less than the IOD at the PRPM, whether induced by TES (5.2 mm) or minimal integrated masticatory EMG activity (5.3 mm). Therefore, it is apparent from this study that the CRPMs and PRPMs provide a scientific means of measuring neuromuscular adaptation to major prosthodontic, or orthodontic, and orthognathic surgical procedures.

Crandall presents an overview of techniques and procedures for evaluating mandibular range of motion in dysfunction patients. The Mandibular Kinesiograph is described as an excellent tool for evaluating both mandibular velocity and movement in three spatial planes.

Crandall, J.A., Evaluation of mandibular movement and range of motion in the diagnosis of craniomandibular disorders. J. of Craniomandib Pract. July 1986, Vol 4, No. 3, pp 234-245.

Dental literature contains a great deal of information on the examination and diagnosis of craniomandibular disorders. Examination of mandibular movement and range of motion can be particularly helpful in obtaining an accurate diagnosis of these disorders.

Mandibular range of motion, as described by Posselt, (Posselt 1968) refers to the objective measurement of the extreme limits of movement in the envelope of motion. Mandibular movement describes the character or quality of the motion required to reach these limits. This article will present a method of recording this information and will propose possible diagnoses based on the results obtained from this examination.

RECORD OF MANDIBULAR RANGE OF MOTION

Pantographic tracings may be taken to provide a permanent record of lateral and protrusive mandibular range of motion. Study models may be mounted on a fully adjustable articulator and the pantographic recordings used to establish the protrusive condylar path, the vertical axis, the mandibular side shift, the terminal hinge axis, and so forth. (Guichet 1977) However, the value of this technique as a diagnostic tool for craniomandibular disorders is limited, and it is impractical to use on every patient complaining of TMJ dysfunction. Its primary purpose is “to diagnose the posterior determinants of mandibular movements (temporomandibular joint characteristics) and to effect a face bow transfer of the maxillary cast” (Guichet 1977) to an articulator for restorative evaluation and fabrication of prostheses.

The Mandibular Kinesiograph is an excellent tool for observing and recording mandibular movements in all three spatial planes. (Jankelson 1980, Hannam, De Cou, et al. 1980) Tracings taken with the patient chewing food provide information about functional or masticatory movements of the mandible. This equipment can also be used to record the range of motion. However, this is an expensive instrument and requires special training in its use. Cost-effectiveness may be a consideration

RECORD OF MANDIBULAR MOVEMENT

Another consideration is the velocity of mandibular movements. (Cooper, B.C. and Rabuzzi, D., 1984) Bradykinesic (slow) and dyskinesic (irregular) mandibular movements are strongly suggestive of restricted function of the craniomandibular complex. Normal movement consists of rapid, uninterrupted acceleration and then deceleration from start to finish. Appropriate treatment will in many instances reduce or eliminate the various types of inhibited movement that accompany craniomandibular dysfunction. The Mandibular Kinesiograph is an excellent tool for evaluation of the mandibular velocity. This instrument can graphically demonstrate the dramatic decrease in mandibular velocity that accompanies muscular dysfunction, pain inhibition, or intracapsular derangement.

In evaluating mandibular movement and range of motion to diagnose craniomandibular disorders, it is critical to keep in mind that recorded information most likely represents a combination of a number of different disorders. The purpose of this examination is to sort out these disorders and to determine the true sources of the patient‟s complaint.
Other forms of craniomandibular disorders exist which cause little or no alteration of mandibular function. Problems such as muscle splinting, myositis and inflammatory arthritis do not alone produce changes in movement or range of motion. It is the inhibitory effects of pain or other associated dysfunctions in combination with these disorders that will result in changes in mandibular kinetics.

CONCLUSION

The primary intent of this paper is to present a simple, straightforward means of recording mandibular movement and range of motion. Using the procedure described above, the examiner should be able to:

1. Determine the incisal vector of deflection from the reproducible “hinge” relation (pathologic or nonpathologic) to the reproducible maximum intercuspation.

2. Visualize and record mandibular range of motion from the maximum intercuspation position in protrusion, lateral movement and maximum opening movement.

3. Evaluate the quality of movement as the mandible travels through the range of motion.

4. Use the recorded information to more precisely determine the true source of the patient‟s craniomandibular complaint and to establish and exact diagnosis.

Evaluation of this information in the diagnosis of craniomandibular disorders must include the following considerations:

1. Deviations from normal movement and range of motion can be used to determine the extent and character of craniomandibular dysfunction.

2. The basic changes in movement and range of motion caused by the identified disorder only.

3. Results of this examination are most likely the composite of more than one dysfunction.

4. Accurate diagnosis of craniomandibular disorders is based on the rational evaluation of as much pertinent diagnostic data as can be reasonably obtained.

Careful observation, attention to detail and the use of new, advanced techniques will aid the examiner in his or her quest to better understand the complexities of craniomandibular disorders and properly diagnose the source of the patient‟s complaints.

STUDIES UTILIZING MANDIBULAR TRACKING FOR RESEARCH PROTOCOLS

Belser and Hannam used mandibular tracking with EMG to examine the effect of occlusal contact on electromyographic activity of the masticatory muscles and patterns of mandibular movement. The study documented changes in muscle activity with different occlusal schemes.

Belser, U.C., and Hannam, A.G. The influence of altered working-side occlusal guidance on masticatory muscles and related jaw movement. The Journal of Prosthetic Dentistry. Vol. 53, No. 3, pp 406-413, March 1985.

MATERIAL AND METHODS

JAW DISPLACEMENT

Simultaneously with EMG activity, jaw displacement was monitored in three planes by means of a noninvasive electronic transducer (Kinesiograph, Myotronics Inc., Seattle, Wash.). Magnetometers carried on a light headframe sensed the movement of a small magnet cemented with self-cured acrylic resin to the labial aspect of the lower anterior teeth in the midsagittal plane. A detailed description of the kinesiographic measurement of jaw displacement has been reported (Jankelson, B., Swain, C.W., Crane, P.F., and Radke, J.C. 1975). If the instrument is properly calibrated, linearized, and combined with the adequate software, it is capable of recording incisor point movement to within 0.3 mm anywhere within the envelope of chewing (Hannam, A.G,, De Cou, R.E., Scott, J.D., and Wood, W.W. 1980). The signals from the three displacement channels were related to three orthogonal planes that passed through the incisor point and included a midsagittal plane and a horizontal plane parallel to the Frankfort horizontal plane. The signals were led to the analog-to-digital converter, sampled, and stored at the same rate as the EMG data.

SUMMARY AND CONCLUSIONS

The effect of four different occlusal situations (group function, canine guidance, working side occlusal interference, and hyperbalancing occlusal interference) on EMG activity in jaw elevator muscles and related mandibular movement was investigated on 12 subjects. With a computer-based system, EMG and displacement signals were collected simultaneously during specific functional (unilateral chewing) and parafunctional tasks (mandibular gliding movements and various tooth clenching efforts) and analyzed quantitatively.

When a naturally acquired group function was temporarily and artificially changed into a dominant canine guidance, a significant general reduction of elevator muscle activity was observed when subjects exerted full isometric tooth clenching efforts in a lateral mandibular position. The original muscular coordination pattern (relative contraction from muscle to muscle) remained unaltered during this test. With respect to unilateral chewing, no significant alterations in the activity or coordination of the muscles occurred when an artificial canine guidance was introduced.

Introduction of a hyperbalancing occlusal contact caused significant alterations in muscle activity and coordination during maximal tooth clenching in a lateral mandibular position. A marked shift of temporal muscle EMG activity toward the side of the interference and unchanged bilateral activity of the two masseter muscles were observed.
The results suggest that canine-protected occlusions do not significantly alter muscle activity during mastication but significantly reduce muscle activity during parafunctional clenching. They also suggest that non-working side contacts dramatically alter the distribution of muscle activity during parafunctional clenching, and that this redistribution may affect the nature of reaction forces at the temporomandibular joints.

Konchak, et al, used sixty-two patients at the University of Saskatchewan to evaluate rest position of the mandible. The study concluded that masticatory muscle relaxation was significantly greater after TENS therapy. Comparative evaluation of adaptive and true freeway showed increased freeway space after TENS, with clinical and true freeway values inversely correlated with the S-N/MP angle.

Konchak, P., Thomas, N., Lanigan, D., and Devon, R. Freeway space measurement using mandibular Kinesiograph and EMG before and after TENS. The Angle Orthodontist, October, 1988, pp 343-350.

Although it is well recognized that the morphology of the craniodentofacial complex has functional influences (Schudy 1964, Sassouni 1969, Paolini 1970), the physiologic parameters influenced by morphology are still not well understood. This investigation expands on a previous pilot study (Konchak et al. 1986) concerned with the identification and correlation of certain morphometric and physiologic properties of the craniofacial complex related to mandibular rest position.

Vertical positioning of the maxillary and mandibular dentitions is dependent on the equilibrium between intrusive environmental forces and the eruptive forces of the supporting tissues acting on the teeth. This balance may be affected by a myriad of factors and variables involving bone, teeth, and soft tissues, including therapeutic efforts such as orthodontics and orthognathic surgery.

Orthodontists and maxillofacial surgeons have traditionally approached these relationships using descriptive methods based on clinical examination and cephalometric and/or dental cast analyses. As these emphasize static rather than dynamic factors, the physiology of the stomatognathic system, and in particular the neuromuscular system, often receive little attention.

A patient’s resting vertical dimension, including the freeway space (FWS), is essentially an adaptive physiologic parameter (Mohl 1978, McNamara et al. 1978). Rest position has been defined as the neutral rest position attained by the mandible as it is involuntarily suspended by the reciprocal coordination of the elevator and depressor masticatory muscles with the upper and lower teeth separated (Niswonger 1934). McNamara et al. 1978 state that rest position is influenced by the activity of the fusimotor system of the elevator muscles through psychic input, and through stimuli from peripheral receptors such as those located in the temporomandibular joint, periodontal ligament, gingiva, tongue and palate:

Jankelson (1977) has described adaptive and true rest positions of the mandible, and thereby adaptive and true freeway spaces. Adaptive freeway space is defined as the interocclusal space that exists when the patient is instructed to voluntarily allow the jaw to relax. True freeway space is the interocclusal space present after relaxation of the masticatory musculature has been achieved, such as occurs following transcutaneous electrical nerve stimulation (TENS) with a myomonitor.

A relaxed muscle is defined as one that is neither contracted nor stretched (Ganong 1985). At this physiologic resting length the muscle is capable of exerting maximal force and maximal velocity under isometric and isotonic conditions respectively. This capability has been explained by the sliding filament theory of muscle contraction which postulates that the maximal availability of cross-bridge reactive sites is present at a muscle‟s physiologic resting length (Huxley 1969).

That masticatory muscle relaxation is achieved following transcutaneous nerve stimulation to the motor division of the trigeminal nerve is confirmed by post-TENS reduction in electromyographic activity, and by an increased muscle response in both force and velocity to electrical stimulation at threshold levels. A spectral analysis of voluntary isometric contraction reveals that fatigue is resolved and not induced by TENS. The power density spectrum frequency maximum shifts from a fatigue level of 75Hz to a relaxed level of 125Hz (Thomas 1987). Comparisons between muscle velocity, force dynamics, and electromyographic spectral analyses confirm that an electrical noise level below 15UV indicates the attainment of physiological resting condition of the masticatory musculature.

After reviewing the results of the pilot study, it was felt that a similar study should be repeated utilizing a larger sample size, and including EMG investigation. The purpose of this research project was to:

1. Determine the percentage of patients who achieved masticatory muscle relaxation following TENS stimulation.

2. Compare adaptive and true freeway spaces.

3. Correlate adaptive and true freeway space values with cephalometric parameters that describe the vertical dimension of the face and facial proportions.

4. Compare freeway space with the Angle classification.

METHODOLOGY

Sixty-two patients seen at the University of Saskatchewan for orthodontic treatment were selected for participation in the study. No criteria for selection were used except that they had to have a natural dentition and be free of symptoms suggestive of temporomandibular joint dysfunction.

Lateral cephalometric radiographs were obtained for each patient with the Frankfort plane horizontal, and with the mandible in the centric occlusion position. From these cephalographs the sellanasion / mandibular plane angle (5- N/MP) and percentage nasal height values were measured to represent common descriptive measurements of the patient’s vertical dimension.

Subjects were seated in a chair and transcutaneous electrical nerve stimulation instrumentation applied utilizing the protocol established by (Jankelson 1977, Jankelson and Radke 1978 and Jankelson 1981). This consisted of the myomonitor, mandibular kinesiograph (MKG) (Myotronics Corp. Seattle, Washington). This is illustrated in the pilot study (Konchak et al. 1987). The surface EMG electrodes were applied over the right and left temporalis and masseter muscles in strict accordance with Jankelson‟s methodology (1981).

EMG recordings were made prior to TENS stimulation, and the adaptive freeway space was measured from the prepulsed vertical dimension of the occlusion. Subjects were then given a minimum of 40 minutes of TENS immediately prior to recording true freeway space values.

It has previously been established by Thomas (1986) that the masticatory muscles are reliably relaxed at EMG values of 14 UV or less, so this EMG criterion was used to group the patients into relaxed and non-relaxed categories.

RESULTS

Four categories of patient groups were established on the basis of the above criteria:

Type A – relaxed before and after muscle stimulation

Type B – not relaxed before or after muscle stimulation

Type C – not relaxed before, but relaxed after muscle stimulation

Type D – relaxed before, but not after muscle stimulation

The average freeway space value before the muscle stimulation was 2.6mm, and after the stimulation it was 3.4mm. These values in the pilot study were 1.8mm before and 2.9mm after stimulation. S-N/MP averaged 33.4 +/- 6.9o, and the percent nasal was 45.4 +/- 2.0%.

It is interesting to note that Group D, albeit a very small sample size, was the only group where the average FWS decreased after TENS. This was the group that demonstrated increased muscle activity after muscle stimulation.

Jankelson (1981) has previously discussed the fact that freeway space has not only a vertical but also an anteroposterior component. He found the A/V (anterior to vertical) ratio to be 1:2, whereby a closing trajectory of the mandible results in a 1mm anterior movement in conjunction with 2mm of vertical movement. This study found an A/V ration of 1:1.8(r=.72), confirming Jankelson‟s findings.

SUMMARY AND CONCLUSIONS

o Four categories of relaxation of the masticatory musculature were determined in patients before and after TENS.

o 58% more patients achieved masticatory muscle relaxation after TENS (50% before, 79% after).

o The average freeway space measurement increased after TENS. Differences for individual patients in their pre- and post-stimulation freeway space values, however, could be either positive or negative, as some experienced an increase in masticatory muscle activity following TENS stimulation.

o Clinical and true freeway space values are inversely correlated with the SN/MP angle, but the correlation values are low.

o Angle classifications were not correlated with freeway space.

o S-N/MP angle and percentage nasal height were inversely correlated.

o No correlation was found between percentage nasal height and FWS. Descriptive factors obtained from cephalometric measurements such as percentage nasal height and S-N/MP angle can be useful in diagnosis and treatment planning, but these values must be correlated with the clinical examination,

o Previously accepted and unchallenged concepts of freeway space and vertical dimension such as those postulated by Guichet (1970) and Lindegard (1953) were not borne out by our application of kinesiographic technology.

In applying FWS values as an aide to orthodontic diagnosis and treatment planning, individual patient values are of greater significance than are group averages. In ongoing studies, individual patient‟s freeway space before and after treatment are being investigated to see whether this parameter is important in influencing the ultimate stability of the occlusion.

Hannam, et al, utilized the Mandibular Kinesiograph and EMG to evaluate muscle activity and mandibular movement. The study concluded that alteration of the occlusion influences muscle contraction patterns and jaw movement patterns during mastication.

Hannam, A.G., et al. The relationship between dental occlusion, muscle activity and associated jaw movements in man. Archives Oral Biol. 22:25, 1977.

SUMMARY

Experiments were carried out on adult subjects before and after occlusal adjustment, and during atypical mastication, to study the relationship between occlusion of the teeth, muscle activity and associated jaw movements. A computer- based system was used to record and analyze the electromyographic activity in the right and left anterior temporal, posterior temporal and masseter muscles, as well as the displacement, in 3 planes, of an incisor point on the mandible. Clinical examination of the occlusion was performed by means of a standard procedure, which permitted numerical values to be assigned to variables commonly observed in clinical practice. Unilateral gum-chewing tasks were carried out by each subject. Five subjects were tested both before and two weeks after occlusal adjustment. Two subjects acted as controls. The series also included one subject with a history of bruxism and another who undertook specific chewing tasks. The results indicated a tendency for occlusal adjustment to be associated with an increase in the lateral excursions of the mandible during jaw closure and, in some cases, with a closer approximation of peak muscle activity to the intercuspal position of the teeth. Specific occlusal features showed no clear association with either muscle activity or jaw displacement, although all subjects developed maximum muscle effort very close to, or at, the intercuspal position. Jaw-closing speed during natural chewing appeared to decrease abruptly before maximum bolus resistance was met by the teeth suggesting the existence of a neuromuscular control mechanism which operates before closing forces become very large.

INTRODUCTION

There is little information available concerning the relationship between muscle activity and jaw movement during normal function in man, despite the significant amount of data which has been accumulated in separate studies of these two parameters (Hannam, Scott and Dc Cou, 1976). As a result, though efforts have been made to relate the state of the dental occlusion to the electromyographic activity in the muscles of mastication, or to patterns of jaw movement, (Ahlgren, 1967; Schaerer, Stallard and Zander, 1967; De Boever, 1969; Troelstrup and Moller, 1970; Gibbs et al., 1971; Griffin and Munro, 1971; Gillings, Graham and Duckmanton, 1973), the lack of quantitation of all three variables at the same time has severely hampered understanding of their precise association during function. The need for a clearer definition of this relationship is confirmed by present approaches to the clinical management of mandibular dysfunction syndromes, when alterations are frequently made to the occlusion to alleviate signs and symptoms of dysfunction in the muscles of mastication, or mandibular joints. While such treatment is often effective, the physiological changes which ensue are poorly understood.

We have described a computer-based system (Hannam et al., 1976) which allows the simultaneous measurement of muscle activity and jaw movement during function. Our present aim was to use this facility to investigate the relationship between selected parameters of dental occlusion, muscle function and jaw movement during unilateral chewing and voluntary clenching tasks in man.

METHODS

Only a few parameters were selected for study from the variety which were recorded. Given the relatively small sample size available at the beginning of an ongoing project, it seemed reasonable to search for associations between those parameters which might have the best correlates. Emphasis was place upon lateral jaw movement in the last few mm of closing, peak muscle activity, the relationship in time of both these parameters to the position of maximum intercuspation of the teeth, and a few selected parameters of occlusion viz, non-working side interferences, interferences in maximum intercuspation, slides from maximum intercuspation, and working side contacts.
The data were obtained from nine adult subjects with natural dentitions. Five of the subjects underwent occlusal adjustment by selective grinding of the teeth between recording sessions, 2 acted as controls for this group, one had a history of bruxism, and one was instructed to perform a forced, vigorous chewing task.

The methods used to assess the electromyographic activity of right and left anterior temporal, posterior temporal and masseter muscles and the movement, in three dimensions, of an incisor point on the mandible, are reported elsewhere (Hannam et al., 1976). Briefly, surface electromyography was used to derive signals from the 6 elevator muscles, and a displacement transducer, consisting of an assembly of magnetometers attached to a headframe, was used to sense the movement of a small magnet cemented to the lower anterior teeth (Kinesiograph, Myotronics Inc., Seattle,

Wash.). After appropriate conditioning, the 9 signals were sampled by a disc-based computer system (HP 2100, Hewlett-Packard, Canada, Ltd.), while the subjects carried out a series of chewing and clenching sequences. Computer samples were taken during the closing phase of 30 right-sided, gum- chewing sequences. 30 similar left chewing sequences and 30 open-close-clench sequences into maximum intercuspation. In addition, voluntary gliding movements made by the subjects with the teeth in contact were used to define the envelope of motion determined by the teeth themselves

DISCUSSION

Alteration of the occlusion by selective grinding clearly appears to influence muscle contraction patterns and related jaw movements in mastication, at least over a 2-week period. The changes wrought in dentition by adjustment tended to standardize the occlusion of each subject. Very broadly, this end-point includes a stable platform in the intercuspal position which is coincident with the most retruded contact position and a freedom from non-working side contacts and posterior contacts in functional lateral and protrusive movements. It is therefore probable that, in the process of reaching these objectives, the removal of premature tooth contacts in centric relation and the removal of non-working side and posterior protrusive guidance, or both, resulted in the changes seen, viz, a tendency to increase the lateral movement of the mandible during closing, and to cause peak muscle contraction to occur more nearly at the position of maximum intercuspatiou.

It is conceivable that in the adjustment procedure, working-side contacts were reshaped in such a way as to allow a flatter approach during jaw closure. This factor was not quantitated, as only the number, position and severity of contacts were recorded. However, it is not likely to have been a major influence on movement patterns, for in the majority of cases the canine teeth made contact in lateral movement before adjustment, and still retained functional contact, albeit more strongly, following adjustment.
On the other hand, it is difficult to differentiate between the effect of removing premature contact in centric relation, and the effect of removing non- working side contacts upon lateral jaw movements, as both procedures were carried out at the same time. It would seem reasonable to attribute increases in lateral excursions to the removal of the non-working side interferences. Ahlgren (1967), for example, has demonstrated that a high percentage of subjects with interferences in centric relation, and a slightly greater percentage with interferences on the non-working side, display chopping masticatory strokes. Although it is not clear from his work, how many times the two kinds of interference occurred together, the larger sample of subjects who demonstrated non-working side contacts implies that this feature alone may have a strong influence upon the degree of lateral jaw movement. However, the relationship between non-working side tooth contacts and jaw movement patterns is far from clear from our study. Even with some fairly large increases in lateral displacement in the small sample, no simple relationship could be demonstrated. Even less explicable is the occurrence in some instances, of reduced lateral movement following occlusal adjustment. Whether it will be possible to demonstrate and explain an association between jaw movement patterns, which are subject to a variety of influences other than the teeth, and tooth contact patterns, when they are recorded by patient-guided or border movement approximations of the opposing dental arches, must await further analysis of larger samples.

Our study shows that there was a tendency, following equilibration, for the peak muscle activity to occur closer both in time and space, to the intercuspal position. The significance of this event is not clear unless other features of the muscle contraction are taken into account. For example, in one subject, despite an insignificant change in a vertical closing pattern after adjustment, the mean peak activity in the right and left posterior temporal muscle actually moved significantly away from the intercuspal position, probably being associated with the significantly slower terminal closing time which occurred following adjustment, as both differences were about 30 msec. However, the total duration of contraction of the right posterior temporal muscle was actually more than doubled, and that of the left posterior temporal muscle more than halved. This example shows that, while peak activity undeniably indicates where maximum effort is reached by the muscles, it does not necessarily indicate how the overall effort is distributed following occlusal adjustment, and as such should not be the only index used in the estimation of force distribution in the closing cycle; for example in the subject with bruxism the muscles were still electrically active at over 50 per cent of their peak response level well in to the intercuspal position, even though peak activity occurred before the position was attained.

The delay between the electrical activity in the elevator muscles and the development of tension is approximately 70-80msec (Ahlgren, 1967; Ahlgren and Owall, 1970; Hannam, Ikster and Scott, 1975) so that peak tension will occur in most instances very close to the intercuspal position, a phenomenon noted by others (Ahlgren, 1967; Ahlgren and Owall, 1970; Gibbs et al. 1971; Gibbs, 1975). It can therefore be reasoned that, if the masticatory system is designed so that high masticatory forces are best withstood in the intercuspal position, the tendency for peak electromyographic activity to move closer to this position following occlusal adjustment may be considered beneficial.
The jaw displacement data recorded from the subject carrying out voluntary chewing tasks are consistent with those reported in a study involving chewing and clenching tasks (Hannam, Inkster, Dc Cou and Scott, 1976) in which mean jaw closing speeds during normal mastication of gum by a group of subjects was 110 mm/sec., contrasting with a speed of closing during voluntary clenching tasks of 183 mm/sec.. Our present study suggests that the resultant closing speed decreases rapidly early in the closing cycle during gum chewing, that at this point the incisors may be quite widely separated, and that significant increases in muscle activity occur much later in the cycle. These results imply that bolus contact, rather than bolus resistance, may be a key influence upon the pattern of normal mastication. The ability of the subject to override this influence voluntarily is shown by the effect of forced mastication, where the usual pattern of mastication is markedly altered, and emphasizes the plasticity of the masticatory system in function.

Belser and Hannam used the Mandibular Kinesiograph and EMG to analyze masticatory EMG activity and mandibular movement during function.

Belser, U.C. and Hannam, A.G., The contribution of the deep fibers of the masseter muscle to selected tooth-clenching and chewing tasks. J. of Prosthet Dent. Nov. 1986, Vol 56, No. 5, pp 629-635.

MATERIALS AND METHODS

PRELIMINARY STUDY

The EMG signals were amplified and filtered by means of optically isolated amplifiers and led to the A to D converter of a disk-based computer (HP 1000 Series E and peripherals, Hewlett-Packard, Canada Ltd.). Sampling of each channel took place every msec, and continuous 5 msec running averages of each rectified muscle response were stored for further analysis. This system has been described in more detail. (Hannam, Scott and De Cou, 1977, Hannam
, De Cou, Scott and Wood, 1977, Hannam and Wood 1981)

Simultaneous displacement of a lower incisor point was recorded in three planes by means of an electronic transducer especially designed for the purpose (Mandibular Kinesiograph, Myotronics, Research Inc., Seattle, Wash.). Each of the three analogue displacement signals was sampled every msec along with the muscle data and stored as a series of 5 msec running averages. A more detailed description of the kinesiographic measurement method can be found elsewhere. (Jankelson, Swain, Crane and Radke, 1975, Hannam, Dc Cou, Scott and Wood, 1980)

Each subject carried out 10 maximum clenching efforts for one second in the intercuspal and incisal edge-to-edge occlusal positions. All clenching efforts were directed vertically to the occlusal plane. The computer generated periodic visual signals to cue the onset and duration of each clenching act. Following the sampling and storage of the associated signals, muscle activity over the central 400 msec of each response was averaged. These averages were used to calculate a task average representing the mean EMG response for the series of 10 efforts.

SUMMARY AND CONCLUSIONS

Anatomically, the human masseter muscle Consists of at least two portions (pars superficialis, pars profunda) with distinctly different fiber directions. The purpose of this study was to describe functional behavior in the deep fibers of the masseter muscle and to define any differences in its behavior from that of the superficial fibers. In 20 subjects, EMG activity of the superficial and the deep portions of the masseter muscle was recorded during specific parafunctional (intercuspal and eccentric tooth clenching) and functional (unilateral chewing) tests. Superficial and deep activity was measured with bipolar surface electrodes and intramuscular fine-wire electrodes. Simultaneously, displacement of a lower incisor point was recorded in three dimensions. The data were collected and stored for analysis by a disk-based computer system.

The results indicated that changes in the direction of effort, in mandibular position, and in the side used for chewing all influenced activity in both parts of the muscle to different extents. The most distinct separation of activity occurred when intercuspal clenching was directed retrusively; the deep fibers of the masseter muscle response reduced to 47.5% of its maximum value while that of the superficial fibers of the masseter muscle fell to 5.5%. During chewing, activity in the deep fibers of masseter muscle was distributed evenly bilaterally, whereas that in the superficial fibers of the masseter muscle was biased significantly toward the chewing side.

Differentiation of activity within the masseter muscle may be relevant to the distribution of regional tenderness in the muscle when it is involved in parafuctional activity. The results suggest that retrusively directed occlusal grinding or clenching behavior, often manifested by wear facets on the molar and premolar teeth can be expected to be associated with strong activity in the deep fibers of the masseter muscle. Tenderness as a consequence of its excessive contraction might therefore be predicted in the preauricular region anterior to the, temporomandibular joint, a region that can be palpated easily during clinical examination.

Neilsen, et al, studied the ability of 17 normal and 33 dysfunction patients to achieve predetermined jaw positions during opening. The data suggested that neuromuscular control is altered in patients with craniomandibular muscle pain, but not by degenerative TMJ changes.

Nielsen, L.L., Ogro, J., McNeil, C., Danzig, W.N., Goldman, S.M., and Miller, A.J. Alteration in proprioceptive reflex control in subjects with craniomandibular disorders. J. of Craniomandibular Disorders: Facial and Oral Pain. Vol 1, No. 3, pp 170-178, 1987.

Proprioceptive reflex control of mandibular positioning was impaired in subjects with mandibular muscle pain. Tracking of mandibular movement, by observing the movement of a reference point placed at the lower incisors, showed that control subjects and patients with muscle pain projected beyond (i.e., overshoot) a predetermined target position before reaching the final point. Patients with muscle pain demonstrated significantly less precision in achieving a predetermined mandibular position and a greater range in the overshoot.

Mandibular position is precisely controlled in the human and is postulated to rely heavily on proprioceptive feedback from the temporomandibular joints (TMJs) and masticatory muscles. (Thilander 1961, Larsson, et al. 1964, Owall 1978, Ramsjo 1963, Christensen, et al 1975, Carraro, et al. 1970, Storey 1976, 1985.) This proprioceptive input synapses both within the trigeminal sensory nucleus and the primary sensory cortex and affects motor trigeminal neurons via reflex arcs to alter craniomandibular muscle activity. (Dubner, et al. 1978)

The ability to repeatedly attain an arbitrary position of the mandible between posture and maximum opening was first reported by Thilander (1961) and Ramsjo and Thilander. (1963) The variation in attaining a predetermined jaw position in normal subjects was found to be 3.4 mm, as tested with a calibrated wood spatula measuring interincisor position between the lowest and highest values. Further work by Thilander (1961) and Christensen and Troest (1975) has shown that anesthetizing the TMJ capsule with its ligaments resulted in an increase in the range in precision of determining mandibular position Christensen and Troest (1975) have shown that applying a local anesthetic to the lateral pterygoid muscle also significantly increased the range of the mandibular kinesthetic test. This study suggests that either sensory feedback from the lateral pterygoid muscle or impairment of the reflex arc controlling lateral pterygoid activity and condylar position modifies the process by which a subject knows and reproduces a mandibular position

METHODS AND MATERIALS

JAW TRACKING

Each subject was asked to sit upright in a chair. A magnet was placed below the mandibular medial incisor using a moisture-activated adhesive (Stomahesive, Squibb). A headgear from the Kinesiograph with magnetic field sensors, modified according to Hannam et al., (1980) was placed on the patient‟s head. (Lewin 1974) Movement of the mandible was tracked in the frontal plane and plotted on an X-Y plotter (Watanabe) at a magnification of 2 x.

The vertical measurements in the frontal plane were corrected for the nonlinearity of the Kinesiograph by means of calibration graphs.

STATISTICAL ANALYSIS

The extent of the maximum opening in the frontal plane was measured first; then the distance from the intercuspal position to each target position; and finally the length of the overshoot beyond the target position. Measurements were completed using a calibrated graph which permitted correction of the measurements for the lack of linearity of the Kinesiograph.

RESULTS

CONTROL SUBJECTS

The control subjects demonstrated a significant difference in the mean range of jaw opening between the <50% opening and the >50% opening. The range was greater at the >50% jaw opening (P< .025) than at the <50% mandibular opening. The overshoots at both the <50 and the >50% jaw openings were similar and not statistically different.
At <50% Jaw Opening. The range and standard deviations were compared between the four groups of patients with muscle pain and the normal subjects. None of the patients with muscle pain and the subjects with pain in both head and neck muscles, including the subgroup with joint degeneration, demonstrated a greater range or standard deviation than the control subjects. However, the subgroup with pain in the masticatory muscles only (and no pain in cervical or neck muscles) demonstrated a significantly greater range (P<0.05) and less precision than the normal subjects.

At >50% Jaw Opening. In contrast to the results at the small mandibular opening, patients with muscle pain demonstrated a significant increase in the range of reaching the same mandibular position when tested at >50% of their maximum opening. Patients in the broadest category of muscle pain, those subjects with pain in masticatory and cervical muscles, and those with such pain and joint degeneration, demonstrated significantly greater ranges than normal subjects. This finding was supported by the analysis of the standard deviation which showed that the patients with pain in both masticatory and cervical muscles, and subjects with joint degeneration, exhibited larger standard deviations. The only group of patients that did not exhibit a significantly different range were those with pain only in masticatory muscles. These subjects exhibited greater ranges only at the smaller jaw opening of <50%.

Overshoot at <50% Jaw Opening. The overshoot is the linear distance by which a subject exceeds the predetermined opening. In the control subjects, the range and standard deviation of the overshoot was similar between the small mandibular opening at <50% and the larger opening at >50% in the midrange of total excursion. Comparing the four groups of patients with the normal subjects at the small jaw opening of <50% showed that the range did not vary between the groups (P<0.05).

Overshoot at >50% Jaw Opening. The patients with muscle pain and with pain only in the masticatory muscles, or pain in both head and neck muscles with or without joint degeneration, demonstrated significant increases in both their ranges and standard deviations of their overshoots at the >50% opening as compared to the control subjects. All patients, regardless of the location of the pain or whether the joint demonstrated degenerative changes, showed significant increase in the degree of overshoot as defined by both the range and standard deviation.

DISCUSSION

Our study, using jaw tracking with the Kinesiograph, shows that subjects will exceed the pre-determined target position and then return to this position. This overshoot was similar for the two mandibular positions tested in normal subjects. The overshoot may represent a normal delay in the comparison of the sensory feedback to the descending motor signal. This sensory feedback indicates the actual length of the muscle spindles in the jaw elevator muscles and includes input from the joint receptors that continuously discharge during increasing movement of the mandible.

SUMMARY

Seventeen normal subjects and 33 subjects with masticatory muscle pain were studied for their precision in actively attaining predetermined mandibular positions during jaw opening. The subjects were seated upright in a chair without head support. With their eyes closed, they were then requested to open their mouth to one of two arbitrary mandibular positions selected by the investigator. The subjects maintained this position for 20 seconds and then closed and repeated the same opening in ten trials of opening and closing.

The reproducibility of two different jaw openings; one at approximately <50% of the maximum mandibular opening; and one at >50% of the maximum opening was then tested. The mean, standard deviation, and range for each of the series of ten trials were determined. The movement of the mandible during this test was tracked with the Jankelson’s Kinesiograph, in which a magnetic sensing system recorded the movements of a small magnet placed at the mandibular incisors.

The control subjects demonstrated a significant increase in the range of opening in the ten trials (P<.025) and the >50% jaw opening level as compared to the <50% opening. The jaw tracking provided precise recording of the movement pattern in the frontal plane and showed that subjects usually opened wider than their predetermined target position and then closed to the determined position. The range of variation of the “overshoot” did not differ significantly between the <50% and >50% jaw opening trials indicating normal subjects overshot their target position to the same degree for both mandibular openings.

Subjects with muscle pain were divided into three subdivisions: (1) those with pain in both masticatory and cervical muscles (N =33); (2) pain in mandibular muscles only (N = 5); and (3) pain in mandibular and cervical muscles with joint degeneration (N = 10). In the mandibular position tested at the small opening (<50%), only the group with masticatory muscle pain demonstrated a significant difference in comparison to the control group (N = 17). At the larger opening (>50%), all subjects with muscle pain, the subjects with pain in mandibular and cervical muscles, and the subjects with pain in these muscles and joint degeneration all demonstrated a significantly greater range and less precision. Subjects with pain only in the masticatory muscles did not demonstrate significant differences at the larger opening possible due to the small sample.

At the small opening, i.e., <50% of the maximum, the subjects with muscle pain did not demonstrate any difference in the range and standard deviation of the overshoot. In contrast, both the range and standard deviation for the overshoot were significantly larger in all patients with muscle pain and their subcategories as compared to normal subjects when tested at the >50% opening.

These data suggest that the neuromuscular control with which an individual determines mandibular position is altered in subjects with craniomandibular muscle pain, but not further influenced by degenerative joint changes within the temporomandibular joint (TMJ).

Neill and Howell used the Mandibular Kinesiograph to analyze mandibular movement in 97 young adult patients. Data conclusions were preliminary and further investigation is being conducted.

Neill, D.J. and Howell, P.G.T. Computerized kinesiography in the study of mastication in dentate subjects. J. of Prosthet Dent. May 1986, Vol 55, No. 5, pp 629-638.
In an attempt to achieve a better understanding of the chewing mechanism, research has been directed at identifying the nature of jaw movement together with observations of the associated neuromuscular control.

Beck and Morrison (Beck and Morrison 1962) reported the development of the mandibular replicator with extraoral frameworks that attached to the teeth of both jaws. The replicator carried sensors located in three widely separated points and monitored the spacial movement of the mandible. Although a number of researchers have used this or a similar apparatus to reveal valuable information concerning border movements and condylar shift, the nature of the equipment so intrudes on the subject’s level of consciousness as to render it unsuitable to record the movements that occur in normal function.

Although tracing the movement of a single point on the mandible has limitations on the interpretation of jaw movement, it has merit of requiring less obtrusive markers. The earliest recorded studies of single-point movement are attributed to Luce (Luce 1889) who in 1889 used still photography to record the path of movement of a light source attached externally to the mandible. Hildebrand, (Hildebrand 1931) reporting his cinephotographic and cineradiographic experiments on masticatory movement, included a review of the literature in 1931. Ahlgren (Ahlgren 1966) and others have since used a similar technique necessitating immobilization of the subject‟s head to ensure that the recorded movements were those of the mandible alone.

The Mandibular Kinesiograph (Myotronics Research Inc., Seattle, Wash.) (Jankelson, et al. 1975) and the Sirognathograph (Siemens AG, Bereich Medizinishe Technik, Kaufmannishelietung, Germany) (Lewin, et al. 1974) both enabled jaw movement to be monitored without the head being restricted and without the need for any connection between the intraoral marker and the transducing element. Both depended on a change in magnetic flux occurring when a small bar magnet attached to the labial aspect of the mandibular incisor teeth moved relative to sensors mounted on the framework attached to the subject‟s head.

The relative merits of the two instruments have been investigated and reported. (Neill 1984) The Kinesiograph proved to be the more versatile of the two instruments and has been used in our studies. It was capable of being linked by way of an analogue to digital converter to a micro-computer for the storage, retrieval, and analysis of data. Calibration of the equipment was done and a short computer program written in Basic corrected errors and ensured a linear response.

RESULTS

PATTERN OF JAW MOVEMENT: SAGITTAL PLANE

Whenever tooth contact occurred it appeared to be in centric occlusion. Although some subjects consistently showed the opening stroke to be in front of the closing stroke, in others as many as 50% of the closing strokes occurred in a forward position. The angulation of the sagittal pathway was normally directed upward and backward, reflecting the rotational element in mandibular opening, but this tended to be more vertical with those subjects having a deep incisor overlap.

DIMENSIONS OF THE CHEWING CYCLE

The mean lateral range of movement varied from 4.9 mm to 6.7 mm. Men had a wider lateral range than women. Irrespective of sex, the range of lateral movement was generally less for subjects with a Class II, division 2 dentition.

The mean maximum vertical opening varied from 14.5 mm to 18.7 mm and again, irrespective of the test food, men had a greater opening than women. The widest separation and lateral deviation for all groups and both sexes was found in the chewing of cookies.

CYCLE TIME

The mean cycle times varied from 0.73 secs to 0.86 sees. Despite the smaller range of jaw movement in women, the cycle time was longer for all of the test foods. The cycle times were greater for beef and chewing gum than for other foods, which were not significantly different.

TOOTH CONTACT SLIDE

By amplifying the portion of the chewing cycle adjacent to tooth contact and tooth guidance in lateral excursion, it has been possible to measure the length of the tooth contact glide into and out of the intercuspal position for a group of 33 subjects. This ranged from 0 to 4.5 mm and the mean values for each subject were determined.
The combined values of closing and opening slides pooled for subjects in the four different orthodontic groups and for the five different foods are shown in Table VIII. They range between 1.38 mm and 2.8 mm and in each group the longest contact glide occurred with peanuts.

CONCLUSIONS

The chewing activities of 97 young adult subjects were studied by analyzing the movement of a single point on the mandible in the frontal and sagittal planes.
Differences were found between men and women with respect to cycle time, velocity of movement, dimensions of the chewing envelope, and the duration of the pause in the intercuspal position. The nature of the test food also had a bearing on the values of each of these parameters.

The subjects were grouped according to incisor relationship which appeared to have some bearing on the extent of the tooth contact slide and the path of movement in the sagittal plane. However, the data on which these observations were made were too small to draw valid conclusions and this aspect of the study will be expanded in a further series of investigations.

Hannam, et al, used the Mandibular Kinesiograph and EMG to quantitate and compare muscle EMG activity and mandibular movement. After evaluation of the advantages and disadvantages of these modalities, the authors conclude that significant information about muscle function and jaw movement during mastication and the effects of conventional occlusal treatments can be obtained.

Hannam, A.G., Scott, J.D., and De Cou, R.E. A computer-based system for the simultaneous measurement of muscle activity and jaw movement during mastication in man. Archs Oral Biol Vol 22, pp 17-23, Pergamon Press, 1977.

SUMMARY

A computer based system was developed in order to analyze the activity of 6 jaw closing muscles and the associated displacement in 3 dimensions, of an incisor point on the mandible, during gum-chewing and clenching sequences. Signals were derived by surface electromyography from the right and left anterior temporal, posterior temporal and masseter muscles, and by means of a set of magnetometers which sensed the movement of a small magnet cemented to the lower incisor teeth. Sampling of those signals by the computer was locked in phase to the chewing cycle, and the digitized signals were conditioned and analyzed by software to permit quanitation of a wide variety of parameters. The system proved non-invasive and allowed repeated measurements to be made on different occasions. It is suggested that the technique should be useful in the study of masticatory mechanisms, and in assessing the effects of clinical alterations to the occlusion

MATERIALS AND METHODS

JAW DISPLACEMENT

Jaw displacement in 3 planes was recorded continuously with a non-invasive electronic transducer (Kinesiograph, Myotronics, Inc. Seattle, Washington) which allowed the movement of a magnet rigidly secured to the mandible to be monitored by a set of magnetometers carried in a light head frame (Jankelson et al, 1975). A small magnet was fixed by means of acrylic cement to the labial surface of the lower anterior teeth and gum, 1 mm below the edge of the upper incisors, the teeth being clenched in maximum intercuspation. The orientation of the magnet was carefully controlled with a modified dental facebow (Whipmix Corp., Louisville, Kentucky) cemented in the midsagittal plane, parallel to the Frankfort plane which was also used as a reference for placing the sensors. These were carried on the head frame of aluminum bars attached to a spectacle frame by an elastic head strap. Precise alignment of the sensors relative to the magnet was accomplished by a set of calibrated blocks.

To create a wide, linear working range for the system, we did not follow the manufacturer’s instructions exactly and the apparatus was bench-calibrated with the top face of the vertical movement sensor 6.9 cm from the top of the magnet and the inside surface of the anterior-posterior movement sensor 4.3 cm from the front face of the magnet. With the gain of the instrument set so that a 4 cm vertical excursion produced -5 V, a + 1 cm lateral excursion + 1 V, and a ÷ 1 cm anterior-posterior excursion + 1 V, the magnet was moved systematically in a three-dimensional lattice with a wooden rod attached to calibrated micromanipulators. Calibration curves were then constructed for each of the 3 planes of movement enabling a linearizing program to be written for the computer so that, after sampling, the displacement data would be automatically corrected. It was possible thus to measure to an accuracy of +0.25 mm, anywhere within the cube 2 cm wide, by 2 cm deep, by 4 cm in height.

To estimate the accuracy which could be expected in day to day placement of the entire apparatus on a given subject, an acrylic bit block was constructed for one subject so that the mandible could be reproducibly placed in an open, lateral and posterior position. On each of 3 separate days, the apparatus was set up on the subject, and the bite block inserted and removed 5 times, readings being taken each time. The mean jaw opening was 19.3 mm. SD + 0.4, lateral displacement 3.2 mm S.D. + 0.8, and antero-posterior displacement 3.5 mm S.D. +1.3 (n=15), the measurements being taken from the intercuspal position relative to the midline sagittal plane, Frankfort horizontal plane and a frontal plane perpendicular to the Frankfort plane. Although it was estimated that the day to day error in recording lateral measurements would be less than 0.4 mm in the last cm of jaw closing, the error in antero-posterior measurements was considered large enough to warrant additional precautions during subsequent use of the system. Therefore, in all later recordings involving repeated measurements of subjects, a bite block at an arbitrary incisal separation of about 15 mm was constructed for each subject and used to check the alignment of the system during every experimental run

RESULTS

Figures 4 and 5 demonstrate mean electromyographic and displacement data collected during sequences of right-sided, unilateral chewing carried out by the same subject on two different occasions, separated by two weeks. Both the patterns of muscle contraction and the patterns of jaw movement determined for this subject are consistent with those reported by Moller (1966) and Ahlgren (1966, 1967a).

The mean contraction patterns appear to be very consistent, and at the same time, demonstrate a feature common to many subject with Class III malocclusions, viz, a tendency to show reduced functional activity in the masseter muscles relative to that in the temporal musculature. The subject in fact had a marked Class III tendency, and confirmation of the apparent decreased functional activity in the masseter muscles was obtained by demonstrating, on both occasions, a 5-fold increase in the mean peak activity of the four temporal muscles relative to the two masseter muscles during the clenching task in the intercuspal position.

Comparison of the two displacement records shows that while the closing strokes were essentially the same in term of lateral deviation of the mandible, the subject opened less widely and more posteriorly during his second trial. This reduced excursive movement was associated with a more rapid chewing cycle, as the time take to reach maximum intercuspation (CO) from maximum jaw opening fell from 498 msec S.D. ÷ 50 in the first trial, to 419 msec S.D. + 35, in the second. However, the ratios of time taken from the 5 mm open position to the time from maximum jaw opening to maximum intercuspation were 0.45 and 0.47 respectively for the two trials, indicating that these two phases of the closing cycle were proportionally the same, despite differences in the overall cycle times. By the time the incisor point was within 2 mm of the intercuspal position, a time when most muscles were very active, the two displacement patterns were essentially identical.

DISCUSSION

The flexibility of the system described permits a wide variety of parameters to be quantitated and compared. It has the advantages of simplicity and comfort so far as the subject is concerned and provides a versatile and readily adaptable system to meet the operator‟s demands. For instance, by increasing the storage facility of the computer, a detailed analysis of jaw opening can be included. In addition, other electrode systems can be used, and other muscles sampled if required. Finally, a variety of methods can be applied to smooth, reduce and quantitate the data.

Two disadvantages of the system are the limitations placed by recording a single point of movement on the mandible, and the use of surface electromyography to assess muscle responses. The former does not permit a reliable assessment to be made of condylar movements during function, and the latter limits the muscles which can be sampled during function. As the price which must be paid to remove these drawbacks is to increase the invasiveness of a system which already must influence normal function to some degree, there would seem to be room for compromise. We feel that even in its present form, the system can provide significant information about muscle function and jaw movement during mastication, and at the same time provide a yardstick for the comparison of the effects of conventional occlusal treatments. (Hannam, Scott, De Cou and Wood, 1976)

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