An evaluation of asymmetry in TMJ radiographs

An evaluation of asymmetry in TMJ radiographs Lawrence A. Weinberg, D.D.S., M.S.* New York. N. Y.

M

any dentists question the clinical value of temporomandibular (TMJ) radiographs because of the asymmetry of the mandibular fossa and condyle in relation to the cranium, as well as one side compared to the other. It is assumed, therefore, that resultant radiograph’s have limited value for diagnosis and treatment. Before this conclusion can be drawn the effect of TMJ asymmetry should be evaluated experimentally. In order to avoid superimposition of the cranial bone into the image of the TMJ any lateral transcranial TMJ radiographic technique requires anterior and inferior angulation of the head in relation to the film.‘~” This orients the condyle being radiographed perpendicularly to the film in three dimensions.” Paradoxically, the three-dimensional head position that is required for a TMJ radiograph accomodates condylar asymmetry and aligns that condyle almost perpendicularly to the film.6 Due to the 75” angulation of the x-rays to the film the lateral third of the mandibular condyle and fossa is outlined on the radiograph in profile or as a crosssectional view and not in a “composite” view of an irregular body, as is commonly thought.” Cranial structures severely limit the degree of allowable variation in head position when pro4ucing a diagnostic TlMJ radiograph.” The radiographs have been shown to be duplicable to within approximately 0.2 mm.’ The purpose of this article is to measure and evaluate the asymmetry of the mandibular fossa and condyle by comparing one side with the other. This is necessary because evidence has shown that the mandibular condylar position in the fossae is significantly related to clinical symptoms.8-‘5 Also the treatment of TMJ problems is often based on condylar repositioning.“’ “. “-u It is appropriate to rule out the possibility that asymmetry between the

*Director, Medical

TMJ w-vice, Dental Center, East Meadow.

(w)z~-3913/78/0240-0315500.90/0rn

Department, N. Y.

Nassau

1978 Tbe C. V. Mosby Co

County

Relative dimensions of joint space indicates condylar posit ion

Normal condylar position

Re truded condylar position

Fig. 1. The condyle is retruded because the posterior joint joint space is reduced compared to the anterior space. right and left sides could account for these findings. If the asymmetry of these structures is found to be statistically insignificant the findings and clinical procedures reported have increased validity.

METHOD AND MEASUREMENT Most often, in the treatment of TMJ dysfunctionpain syndrome, the diagnostic significance of the TMJ radiograph is in the interpretation of condylar position within the fossae.‘J-‘x The relative dimensions of the anterior and posterior portions of the superior joint space indicate this condylar position (Fig. 1). The condyle is retruded when the posterior joint space is less than the anterior joint space (Fig. 1). In over 98’70 of patients studied the superior portion of the fossa is symmetrical and forms an arc of a circle. The fossa can be measured utilizing segments that are 3.5 mm in length ~Fig. 2). For research purposes the radiograph is projected and enlarged 14 times normal size, and tracings are made of the mandibular fossa and condyle and the auditory meatus for orientation purposes (Fig. 3). A

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Measuring system oriented to superior portion of TMJ fossa

Art emi

Fig. 2. The fossa is measured utilizing

Tracing of TMJ 14x normal size

PHOTO ENLARGEMENT TECHNIQUE

TMJ

x-ray

projected

Fig. 3. Enlarged tracings are made of the mandibular MEASUREMENT

3.5 mm segments.

TEMPLATE

fossa, condyle, and auditory meatus.

FOSSAEASYMMETRY The left TMJ radiograph was reversed when projected so that the tracings could be superimposed on each other for comparison. The center (C) of the superior portion of the two fossae were superimposed and the tracings were rotated around that point until the anterior and posterior differences in the arcs were equal (Fig. 6). The difference between the two tracings was measured at the anterior and posterior joint space location.

CONDYLAR ASYMMETRY

Fig. 4. A template is used to orient and record the joint spaces. template (Fig. 4) and a measuring system were developed to orient and record the joint spaces (Fig. 5). The system was shown to be statistically valid to within f 0.1 mm.’

316

The comparison between the condyles on the right and left sides is more difficult because of variation in condylar position within the fossae (Figs. 7 and 8). A line was drawn tangent to the condyle and perpendicular to the center line (C) on the right tracing (Fig. 7). By comparing Figs. 7 and 8, it can be seen that, due to the change in condylar position, a slightly greater portion of the condyle will be measured on the displaced condyle (Fig. 8). While keeping the center lines paralief -the left

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Center of superior of TMJ fossa

portion

Measure’ment template Fig. 5. The tracing of the condyle and fossa is superimposed over the template. condyle tracing was moved along the horizontal line until the anterior and posterior differences were equal (Fig. 9). The tracings were not rotated because the diagnostic measurements are always made relative to the superior portion of the fossa. Therefore, to be valid, the comparison of the condyks should be made relative to the same planes of reference. Rotating the tracings of the condyles would produce less variation. However, it would not be valid since the object is to measure asymmetry relative to the diagnostic procedure, not relative merely to an abstract shape without a plane of reference.

CENTER OF SUPERIOR PORTION OF FOSSAE SUPERIMPOSED

RESULTS Fossae Asymmetry

FOSSAE TRACINGS ROTATED AROUND CENTER (C) UNTIL ANTERIOR Ei POSTERlCf?

Seventy acute TMJ patients and 70 control patients from genera1 practice were numbered and measured randomly to eliminate experimental bias. The measurements were reduced mathematically by a factor of 14 (the tracings were enlarged to 14 times normal size) and analyzed statistically. Rounded figures are shown in the illustrations for simplicity, but exact figures will be used in this text. Acute TMJ group. In the 70 acute TMJ patients the mean (average) difference in the shape of the fossae due to asymmetry between one side and the other was 0.168 mm. This represented only 7.5% of the mean posterior joint space and 6.4% of the mean anterior TMJ space (Fig. 10). Control group. In the 70 control patients from

DIFFERENCES

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Fig. 6. The tracings of the left TMJ are reversed and superimposed on those of the right TMJ for comparison. general practice the mean difference in the shape of the fossae due to asymmetry was 0.155 mm. This represented only 6.57~ of the posterior and anterior TMJ spaces (Fig. 11). Condylar

Asymmetry

Acute TMJ group. The mean difference in the shape of the mandibular condyles in the acute TMJ patients due to asymmetry was 0.201 mm. This represented only 8.9% of the mean posterior joint

WFINBERC;

LEFT

RtGHT TMJ TRACtNG

TMJ

TRACING

(radiograph

reversed)

I

line drawn tangent to condyte, I to center

CONCENTRK

0

CONDYLE

IO :

RETRUDED

CONDYLE,

Fig. 7. The line is tangent to the condyle and perpendicular to the center line (C) on the right tracing. Fig. 8. A slightly greater portion of the condyle is measured with a displaced condyle. ”

CENTER LINES PARALLEL POSTERIOR

In /-

ANTERIOR DIFFERENCE IZONTAL LINE

LEFT CONDYLE TRACING MOVED ALONG HORIZONTAL :.INE UNTIL ANTERIOR t3 POSTERIOR DIFFERENCES

ARE EQUAL

Fig 9. The left mandibular condyle tracing has been moved along the horizontal line until the anterior and posterior differences are equal. space and 7.7% of the mean anterior joint space (Fig. 12). Control group. In the 70 control patients from general practice the mean difference in the shape of the condyle due to asymmetry was 0.207 mm. This represented only 8.7% of the mean posterior joint space and 8.6% of the mean anterior joint space (Fig. 13). STATISTIC AL ANALYSIS An average or mean of any group of measurements has no real comparative value without statistical analysis to express the distribution of the values 318

around that average. The 95% level of probability is often used to express this distribution. A 95% prabability level indicates that if additional samples of the same size were drawn from this population, in the same manner, we would expect that for 95% of-the time the mean taken from the new sample would fall within a specific range of the mean of the first group. This expresses the confidence limits, or the range of variation, expected 95% of the time. Fossa asymmetry. In the 70 patients with acute TMJ problems the average difference in the shape of the fossae due to asymmetry between the right and left sides was 0.168 mm. At the 95% per cent level of probability a new sample would be expected to produce the same average 0.168 mm difference within a range of +- 0.033 mm (Fig. 14). In the control group the average difference in the fossae due to asymmetry between the right and kft sides was 0.155 mm. At the 95% level of probability a new sample would be expected to yield the same mean value (0.155 mm) within a range of + 0.031 mm (Fig. 15). Condyler asymmetry. A similar 95% level of probability was worked out for the mandibular condyles in the two groups. In the original 70 acute TMJ patients the average difference between ,the right and left condyles due to asymmetry was 0.201 mm. A new sample would be expected to yield the same mean value (0.201 mm) within the range of zt 0.041 mm (Fig. IS). SEPTEMBER

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ACUTE TMJ, 70 CASES

Oa17mm.

Fig. and Fig. and

0.17mm.

I’

G.P. CONTROL, 70 CASES

I

OnI6mm,

0.16mm.

10. The mean difference in the shape of the fossae, due to asymmetry, between one side the other in the acute TMJ group is 0.17 mm. 11. The mean difference in the shape of the fossae due to asymmetry between one side the other in the control group is 0.16 mm.

rACUTE

TMJ, 70 CASESf

0.2 mm. -1

0.2 mm.

G.P. CONTROL, 70 CASES

0.2mm.

0.2mm.

18% OF AJSl

0 Fig. 12. The mean difference in the shape of the condyles due to asymmetry between one side and the other in the acute TMJ patients is 0.2 mm. Fig. 13. In the control group the mean difference in the shape of the condyle due to asymmetry between the right and left sides was 0.2 mm.

The original 70 patients in the control group demonstrated an average difference of 0.207 mm between the right and left condyles due to asymmetry. A new sample would be expected to produce a similar mean difference of 0.207 mm within the range of + 0.039 mm 95% of the time (Fig. 17). Summary. Variation in the shape of the mandibular fossa and condyle due to asymmetry between the right and left sides is extremely small (approximately 0.2 mm) and is not observable with the naked eye. This difference represents less than 9% of the total joint space. On this basis the asymmetry of the THE JOURNAL

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TMJ, when comparing the right and left sides, is clinically insignificant. Statistical analysis of the data reveals that for 95% of the time a completely new sample would yield similar resuhs within a range of + 0.04 mm.

COMFARISON BETWEEN THE ACUTE TMJ GROUP AND THE CONTROL GROUP A comparison should be made to see if there is a qualitative difference in symmetry. The t-test is a method of evaluating the significant difference between two sample means (acute TMJ compared to 319

Fig. 14. In the acute TMJ patients a new sample would be expected to produce the same average difference in the shape of the fossae, within a range of -t 0.033 mm. Fig. 15. In the control group a new sample would be expected lo yield the same mean difference in the shape of the fossae, within a range of 5 0.031 mm.

AVERAGE 0.20lmm.-+

DIFFERENCE 0,041

AVERAGE DIFFERENCE 0,207 mm.f 0,039

Fig. 16. In a similar acute TMJ group, a new sample would be expected to yield the same mean difference in the shape of the condyles within the range of 2 0.041 mm. Fig. 17. If a new sample were drawn from a general practice group it would be expected to produce a similar mean difference in the shape of the condyles within the range of i 0.039 mm.

the control group) at the 95% level of probability. The values are given in Fig. 18 for the fossa; it was found that there was no statistically significant difference in the findings between the acute TMJ patients and the control group. Fig. 19 gives the data for the comparison in mandibular condylar shape between the two groups. The t-test reveals that there is no statistically significant difference in findings

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when comparing the asymmetry of the condyles between the acute TMJ group and the control group. Summary. At the 95% level of probability or confidence limit there was no statistically significant difference in findings between the acute TMJ group and the control group. This is important to establish experimentally because the high incidence of TMJ-

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T TEST FOR SIGNIFICANT DIFFERENCE BETWEEN 2 SAMPLE MEANS AT 95 % LEVEL OF PROBABILITY I

I

-

fTMJ CASES} CONTROLS .~

O.l55mm, 0.168mm. mean standard 0.017mm. O.O16mm, er for 0.56 not significant 1 T value 1 F Fig. ~3. For the mandibular fossa no statistically significant difference was found between the acute TMJ groups and the control group.

I

T TEST FOR SIGNIFICANT DIFFERENCE BETWEEN 2 SAMPLE MEANS AT 95% LEVEL OF PROBABILITY I

Fig. 19. No statistically significant difference was found when comparing the asymmetry the mandibular condyle between the acute TMJ group and the control group. dysfunction in relation the fossae”. asymmetry, changes in

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pain symptoms that have been reported to mandibular condylar displacement in *‘. ” cannot be attributed to anatomic distortions in the radiographs,6, ’ or head position.’

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SOURCE OF CONTROVERSY The accuracy and value of the lateral transcranial TMJ radiograph has been a controversial subject.2* It is suggested that some, but not all, of the conflict is based on a lack of common terminology. The diag-

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C\“tllrrBER<,

I

PJS

DIAGNOSTIC AREA

CONDYLEg2

NOT AFFECT DIAGNOSTIC AREA I

Fig. 20. The diagnostic region of the glenoid fossais limited to the superior portion. The anterior AJS and posterior joint spaces PJS determine condylar position within the fossa. The diagnostically size.

significant portions of the fossa and condyle are therefore relatively

nostic region used to determine condylar position in the glenoid fossa is limited to the superior portion of the fossae (Fig. 20). A perpendicular line is dropped from the anterior limit of this portion of the fossa, which is called the anterior joint space (AJS) (Fig. 20). A similar procedure is used at the posterior limit of this portion of the fossa, which is called the posterior joint space (PJS) (Fig. 20). The relative dimensions of the anterior and posterior joint spaces determine if the condyle is in the middle of the fossa or displaced posteriorly or anteriorly.” Because of this procedure the distance measured on the mandibular condyle is less than the superior portion of the fossa, since the lines drawn perpendicular to the fossa converge toward the condyle (Figs. 2, 5, 7, and 8). As a result of the geometry it is possible to have marked condylar asymmetry (condyle No. 1 and No. 2, Fig. 20) in the anterior and posterior limits of the condylar head. At the same time it is possible to have very little difference in shape in the small area (between posterior joint space (PJS) and anterior joint space (AJS), Fig. 20) which is used to determine condylar position in the fossa. SUMMARY The asymmetry of the mandibular fossae and condyles were measured to determine if there was a significant difference when comparing one side with the other. After all measurements were taken the test
limited in

and 70 control patients from general practice. It was found that the average differences between the right and left fossae of the TMJ and control groups were 0.17 mm and 0.16 mm respectively. Similarly the average difference between the right and left mandibular condyles of th e two groups was approximately 0.2 mm. The differences in symmetry, obtained by comparing one side with the other, were clinically insignificant. There does not seem to be any reasonable possibility that the high incidence of TMJ dysfunctionpain syndrome reported in association with condylar displacementX-lI, 14-l(iis a result of fossae asymmetry or condylar asymmetry between the right and left sides. The controversy may be partially resolved in that only the superior portion of the fossa and a proportionally smaller part of the condyle are used to determine condylar position in the fossa. Marked asymmetry in the extreme anterior and posterior portions of the two mandibular condyles would not necessarily produce a significant difference in shape in that small part of the superior portion used to determine condylar position in the fossae. Based on this and previous research, the conclusion can be drawn that condylar displacement in the fossa cannot be attributed to distortion in the radiographs, changes in head position, a lack of accuracy, or asymmetry of the mandibular condyles and fossa relative to the cranium or from one side to the other. SEPTEMBER

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REFERENCES

14. Weinberg, L. A.: The role of condylar positiwr in ‘I’MJ dysfunction pain syndrome. (unpublished) 15 Bassette, R., Mohl, N., and DiCosimo, C.: Comparison of results of electromyographic and radiographic examinations in patients with myofacial pain-dysfunction syndrome. J Am Dent Assoc 89:1358, 1974. und Zahnolljusiorl. Dtsch 16. Gerber, V.: Kiefergelenk Zahnarztl Z 26:119. 1971. 17. Harris, H. L.: Effect of loss of vertical dimension on anatomic structures of the head and neck. ,J .4m l)rnt Assoc 25:175, 1938. 18. Block, L. S.: Diagnosis and treatment of disturbances of the temporomandibular joint, especially in relation to vertical dimension. J Am Dent Assoc 34253, 1947. 19. Shore, N. A.: Occlusal Equilibration and Temporomandibular Joint Dysfunction. Philadelphia, 19-59,,J. R. Lippincott Company, pp 165-166. 20. Weinberg, L. A.: Superior condylar displacement: Its dia%nosis and treatment. J PROSTHET Dew 34359, 1975. 21. Weinberg, L. A.: Anterior condylar displacement: Its diagnosis and treatment. J PROSTHET DENY 34:195, 1975. 22. Weinberg, L. A.: Posterior bilateral condylar displacement: Its diagnosis and treatment. J P~osrcw~ &NT 36:426, 1976. 23. Weinberg, L. A.: Posterior unilateral condylar displacement: Its diagnosis and treatment. 38:192, 1977. 24. Klein, I. E., Blatterfein, L., and Miglino, J. I:.: Comparison of the fidelity of radiographs of mandibular condyles made by different techniques. J PROSTHET DI’.ICT24:419, 1972,

1. Weinberg, L. A.: Techniques for temporomandibular joint radiographs. J PROSTHETDENT 28:284, 1972. 2. Riesner, S. E.: Roentgen technique for the mandibular joint. Int J Ortho Oral Surg 23:740, 1937. 3. Grewcock, R. J. G.: Simple technique for temporomandibular joint radiography. Br Dent J 94zl52, 1953. 4. Updegrave, W. J.: Evaluation of temporomandibular joint roentgenography. J Am Dent Assoc 46:408, 1953. 5. Lindblom, G.: Technique for roentgenographic registration of the different condyle positions in the temporomandibular joint. Sartryck ur Skandinavish Tannlaegeforeming 26:193, 1936. 6. Weinberg, I.. A.: What we really see in a TMJ radiograph. J PROSTHET DENT 30:898, 1973. 7. Weinberg, L. A.: An evaluation of duplicability of temporomandibular joint radiographs. J PROSTHET DENT 24:512, 1970. 8. Ramfjord, S. P., and Ash, M. M.: Occlusion. Philadelphia, 1966, W. B. Saunden Company. 9. Lindbloom, G.: Disorders of the temporomandibular joint: Causal factors and the value of temporomandibular radiographs in their diagnosis and therapy. Acta Odontol Stand 11:61, 1953. 10. Farrar, W. B.: Differentiation of temporomandibular joint dysfunction to simplify treatment. ,J PROSTHET DENT 28:629, 1972. 11. Weinberg, L. A.: Correlation of temporomandibular dysfunction with radiographic findings. J PROSTHET DENT 28:5 19, 1972. joint function and its 12. Weinberg, L. A.: Temporomandibular effect on centric relation. J PROSTHET DENT 30:176, 1973. 13. Weinberg, L. A.: Temporomandibular joint function and its effect on concepts of occlusion. J PROSTHET DENT 35:553, 1976

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