To evaluate the position of the condylar head in the glenoid fossa (condylar position) in the intercuspal position, various methods have been employed. However, no standard evaluation method has been established. In addition, the correlation between the condylar position and TMJ internal derangement has not been elucidated. We designed a new, simple evaluation method for the condylar position. Furthermore, the correlation between the condylar position and articular disc displacement was examined. Subjects: A total of 160 TMJs of 80 TMD patients examined by tomography and MRI were included in this study. METHODS: Tomogra-phy was used to evaluate the condylar position in the antero-posterior and supero-inferior direc-tions using our evaluation method as follows; (1) Three segments, the anterior (=a), posterior (=b) and superior (=c) joint spaces as shown by tomography were measured . (2) To evaluate the condylar position, 3 acquired values were substituted for 2 numerical expressions. Each antero -posterior and supero-inferior condylar position was expressed in APR and SIR quantitatively.
APR=b-a/b+a× SIR=(a+b/2-c/a+b/2+c)×100
Articular disc positions were evaluated in 3 positions by MRI. The 3 positions were as follows; superior disc position: the articular disc was in the normal position, slightly anterior disc posi-tion: a part of the posterior band of the articular disc was between the articular eminence and condylar head, completely anterior disc position: complete anterior displacement of the articular disc. The differences among the condylar position of the TMJs of the 3 positions were statisti-cally examined. RESULTS: A total of 157 TMJs were quantitatively evaluated in 2 directions. Three TMJs could not be evaluated with this evaluation method. Significant differences were found concerning the anteroposterior direction between the superior disc position and the slight-ly anterior disc position (p=0.021), as well as the superior disc position and the completely anterior disc position (p=0.047). Significant differences were detected in the supero-inferior direction between the superior disc position and the completely anterior disc position (p<0.001), as well as the slightly anterior disc position and the completely anterior disc position (p=0.020). CONCLUSION: A simple and useful method to evaluate the condylar position was designed. A correlation between the condylar position and articular disc displacement was found.
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