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Temporomandibular Joint Disk Displacement: Comparison in Asymptomatic Volunteers and Patients¹

¹ From the Eastman Dental Center, Rochester, NY, and the Department of Maxillofacial Radiology, Faculty of Dentistry, University of Oslo, PO Box 1109, Blindern, 0317 Oslo, Norway (T.A.L.); the Department of Radiology, Division of Neuroradiology, University of Rochester School of Medicine and Dentistry, NY (P.L.W.); and the Department of Oral Radiology, Showa University School of Dentistry, Tokyo, Japan (T.S.). Received January 18, 2000; revision requested March 15; revision received June 22; accepted July 14. T.A.L. supported by the Research Council of Norway. P.L.W. supported by National Institutes of Health grant number 8053. Address correspondence to T.A.L. (e-mail: larheim@odont.uio.no).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
PURPOSE: To compare the prevalence and type of temporomandibular joint (TMJ) disk displacement in asymptomatic volunteers with those in patients.

MATERIALS AND METHODS: Bilateral oblique sagittal and oblique coronal intermediate-weighted magnetic resonance (MR) images of the TMJs in 58 patients with pain and dysfunction were analyzed and compared with corresponding MR images of 62 asymptomatic volunteers.

RESULTS: Forty-five (78%) of 58 patients had disk displacement compared with 22 (35%) of 62 asymptomatic volunteers. Complete disk displacement was found in 46 (40%) of 115 joints in patients compared with three (2.4%) of 124 joints in asymptomatic volunteers, whereas partial disk displacement occurred in 26 (22.6%) and 27 (21.8%) joints, respectively. Two types of complete disk displacement, anterolateral and anterior, occurred frequently in patients, seldom in volunteers. Only minor differences were found between other types of disk displacement when prevalence in patients was compared with that of volunteers. The disk reduced to a normal position on open-mouth images in all joints in the volunteers compared with 76% of the joints in patients.

CONCLUSION: TMJ disk displacement was less prevalent and was of a different type in asymptomatic volunteers compared with patients with pain and dysfunction.

Index terms: Joints, abnormalities, 244.14 • Joints, MR, 244.12141 • Joints, temporomandibular, 244.91

	INTRODUCTION

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It has been shown (1,2) with magnetic resonance (MR) imaging that nearly one-third of asymptomatic volunteers have temporomandibular joint (TMJ) disk displacement. This finding has led clinicians and researchers to conclude that disk displacement might be a normal variant independent of a patient’s symptoms. We think that this is an incorrect oversimplification since, in our clinical work, we have seen differences between symptomatic and asymptomatic individuals with respect to the prevalence and type of disk displacement. Therefore, it was the purpose of this study to use MR images of patients and asymptomatic volunteers to analyze differences in the prevalence and type between the groups.

	MATERIALS AND METHODS

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Fifty-eight consecutive patients (47 women, 11 men; mean age, 29.2 ± 10.8 [SD]; range, 10–63 years) with symptoms and signs in one or both TMJs who were referred for MR imaging constituted the patient group. All patients had pain, and many had clicking, crepitation, and/or locking. Patients with a history of facial trauma, TMJ surgery, systemic inflammatory arthritis, mandibular growth disturbance, or TMJ tumor had been excluded before the 58 patients were identified.

The volunteer group included 62 healthy individuals (29 women, 33 men; mean age, 27.4 ± 5.9 [SD]; range, 20–46 years) without symptoms or signs of TMJ dysfunction. They had never been evaluated or treated for TMJ pain and dysfunction. Previous orthodontic treatment was not an exclusion criterion. These volunteers were selected consecutively as they fulfilled the criteria for inclusion in the study. The volunteers gave informed written consent for the study, which was approved by the human investigation committee at our institutions.

Both patients and volunteers were examined with their mouths closed and open by using the same MR imaging protocol (3). We used a 1.5-T MR imager (Signa; GE Medical Systems, Milwaukee, Wis), a repetition time msec/echo time msec of 2,000/20 and 2,000/80, a 10-cm field of view, 3-mm-thick sections in the oblique sagittal plane (ie, perpendicular to the horizontal long axis of the mandibular condyle) and oblique coronal plane (ie, parallel with the long axis of the condyle), and bilateral temporomandibular base surface coils.

For the present study, the intermediate-weighted images were independently assessed by two of the authors (T.A.L., P.L.W.) who were blinded to the clinical examination findings. In cases of disagreement, an assessment was made by consensus. Eleven categories of disk position with a closed mouth were recorded (Table 1). We modified the nine-category system described by Tasaki et al (2) by dividing the rotational (anterolateral or anteromedial) disk displacements into partial or complete displacements. Partial disk displacement meant that the disk was displaced in only a portion of the joint, whereas complete disk displacement meant that the disk was displaced on all oblique MR sections. The disk position with an open mouth was classified as normal or displaced. All individuals were evaluated bilaterally.

	RESULTS

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Seventy-eight percent of patients had uni- or bilateral disk displacement compared with 35% of asymptomatic volunteers (P < .001). When calculations were based on the number of joints rather than on number of individuals, the corresponding percentages were 62.6% and 24.2% (Table 2). Disk displacement was bilateral in 47% of patients and in 13% of volunteers (Table 3) (P < .001). The distribution of individuals and joints with disk displacement according to sex is given in Table 2, which demonstrates a similar percentage in women and men with disk displacement in the patient group. In the asymptomatic volunteer group, women had disk displacement more frequently than men (P = .043, one-sided test).

View larger version (104K): [in this window] [in a new window] [Download PPT slide]   Figure 1. Oblique sagittal MR images (2,000/20) of the TMJ of a patient show complete anterior displacement of the disk with the mouth closed in A and B and open in C and D. The disk is anteriorly displaced in all portions of the joint: A and C, lateral; B, central; and D, medial. Arrow indicates the posterior band of the disk.

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   Figure 2. Oblique sagittal MR images (2,000/20) of the TMJ of a volunteer show partial anterior displacement of the disk with the mouth closed in A and B and show the normal position of the disk with the mouth open in C. A, The disk is anteriorly displaced in the lateral portion of the joint. B, The disk is in the normal position in the medial portion of the joint. With mouth opening, the disk position normalizes, which indicate disk displacement with reduction. Arrow indicates the posterior band of the disk.

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   Figure 3. Oblique sagittal MR images (2,000/20) of the TMJ in a volunteer show the normal superior position of the disk with a closed mouth in all portions of the joint: A, lateral and B, centromedial. Arrow indicates the posterior band of the disk.

There was 94% (224 of 239 joints) agreement between the two observers in the first interpretation. Thus, in 15 joints there were disagreement, and a final diagnosis was made by consensus.

	DISCUSSION

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TMJ disk displacement was demonstrated in an MR imaging study (4) of asymptomatic volunteers, with a reported prevalence of 31% (13 of 42 imaged joints). In more recent and comprehensive MR imaging studies (1,2), the percentage of joints with an abnormal disk position ranges between 21% and 23%; nearly one-third of the asymptomatic volunteers had an abnormal disk position in at least one TMJ. The present findings are in accordance with these percentages; further, they demonstrate a significantly lower prevalence of disk displacements in asymptomatic volunteers compared with patients.

Many types of disk displacement can be seen in the patients and asymptomatic volunteers (1,2), and a classification system with nine categories has been developed (2). We modified this nine-category system by subdividing the anterolateral and anteromedial displacements into complete or partial subgroups. We did so because there seemed to be a difference between patients and volunteers with respect to partial versus complete types of disk displacements. Statistical analysis showed that 90% (27 of 30 joints) of disk displacements in the asymptomatic volunteers were partial compared with 36% (26 of 72 joints) in the patients. Previous investigators have discussed whether disk displacement is a normal variant, since the prevalence is relatively high in asymptomatic volunteers. Obviously, misleading results may occur if all disk displacements are categorized together into one group. On the basis of our detailed analysis of the type of disk displacement and subcategorization, we conclude that partial forms of disk displacement generally do not seem to be associated with symptoms.

Our functional observations substantiate those of previous studies (1,2,4,5) of asymptomatic volunteers in which only a few individuals had a displaced disk that did not reduce. Thus, findings of asymptomatic volunteers demonstrate that almost all displaced disks normalize with mouth opening, without any clicking sound. This lack of functional disturbance can probably explain the lack of symptoms, but it was also one of the selection criteria in these studies. In patients with disk displacement in the present series, the disk normalized in 44 (61%) of 72 joints, most of which were partially displaced. Actually, only three joints with partial disk displacement did not reduce.

Another characteristic that differentiated patients from volunteers was the high occurrence of bilateral disk displacement in the patient group. This finding is in accordance with those of previous studies (1,2,6–8). The frequent finding of bilateral disk displacement is in strong contrast to our findings in the volunteer group. In the total series of volunteers, bilateral disk displacement was found in 13% compared with 47% in the total series of patients. Disk displacements were bilateral in 61% of the patients and 36% of the volunteers, among those who had displacements. The difference between uni- and bilateral disk displacement in the volunteers supports the findings of previous studies (1,2), although, in the present study, the proportion of joints with unilateral displacement was more pronounced.

The opinion that disk displacement of the TMJ should be a congenital abnormality has been raised, but recently it was strongly disputed with MR imaging findings in 30 infants and young children aged 2 months to 5 years with a mean age of 2.5 years (9). No instances of disk displacement were identified in these 30 young individuals. All had a superior normal disk position, which clearly indicated that disk displacement is not a congenital abnormality, but rather an acquired degenerative process similar to that seen in other portions of the musculoskeletal system. It should be mentioned, however, that no attention was paid to partial disk displacements in that study.

We found a difference between women and men concerning the prevalence of disk displacement among asymptomatic volunteers, although a significant difference was obtained only with a one-sided test. The increased frequency of disk displacement in women compared with that of men is in accordance with previous study findings (1,2). Our finding contradicts one of an earlier study (4) of asymptomatic volunteers, which had a slightly higher percentage of disk displacement in men than in women. Although there were more than four times as many women than men in the present patient series, which substantiates the general view that considerably more women than men are examined for TMJ pain and dysfunction, the proportion of joints with disk displacement in the patient group was almost equal between the sexes.

MR imaging in the oblique sagittal and oblique coronal planes has been shown (10) to be the most accurate imaging modality for determination of the disk position in the TMJ, when compared with gross morphologic findings. A study (11) on the observer variation also showed a small intra- and interobserver variability among experienced examiners. In the present study, all images were interpreted by two radiologists with extensive experience in the evaluation of TMJ MR images, which probably explains the low interexaminer variability. The detailed classification system that was used would probably have increased the observer variability among less experienced examiners.

The frequent observation of anatomic abnormalities in the TMJ that may not be related to the patient’s symptoms emphasizes a need for a good clinical examination. Findings of this examination should be the basis for determining whether the anatomic abnormalities seen on images are related to the patient’s symptoms or are incidental findings. There is no need for treatment of asymptomatic TMJ anatomic abnormalities.

In conclusion, disk displacements in the TMJ of asymptomatic volunteers were less prevalent, less frequently bilateral, and most often partial, as compared with those of patients with TMJ pain and dysfunction, who more often had bilateral and complete disk displacements. The fact that some categories of disk displacement seem to have a greater tendency to be associated with pain than others should be helpful information when images of patients with TMJ pain and dysfunction are evaluated.

	FOOTNOTES

 
Abbreviation: TMJ = temporomandibular joint

Author contributions: Guarantor of integrity of entire study, T.A.L.; study concepts, T.A.L., P.L.W.; study design, T.A.L.; definition of intellectual content, T.A.L., P.L.W.; literature research, T.A.L.; clinical studies, T.A.L., P.L.W.; data acquisition and analysis, T.A.L., P.L.W.; statistical analysis, T.S.; manuscript preparation, T.A.L.; manuscript editing, T.A.L., P.L.W.; manuscript review and final version approval, T.A.L., P.L.W., T.S.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 

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