The author analyzed magnetic resonance imaging (MRI) findings of the temporomandibular joint (TMJ) in asymptomatic subjects to design standardized diagnostic criteria for anterior disc displacement.
Both TMJs were examined on sagittal images in 129 subjects who had no joint noise, joint pain, muscular pain, or limited opening. Two hundred twelve joints in 106 subjects, including 89 men and 17 women 19 to 71 years of age, were examined with respect to morphologic characteristics of the disc, the antero-posterior length of the disc, reduction or non-reduction of the disc, and the relative position of the disc to the condyle.
Discs with reduction were observed in more than 95% of the examined joints, and discs without reduction were more often noted in women than in men. More than 85% of the examined discs were biconcave, and disc deformation was more common in women than in men.
Analysis of the distribution of the posterior band position relative to the top of the condyle, a landmark for identifying anteriorly displaced discs, indicated that the disc was properly located if its posterior margin was within 4 mm from the top of the condyle, and that the posterior margin was positioned anteriorly to the apex of the condyle in 40% of the joints. On the other hand, the central thin zone of the disc, the relation of which to the condyle is another landmark for disc displacement, was antero-inferior to the anterior prominence of the condyle in approximately 12% of the examined joints.
The results suggest that the prevalence of anterior disc displacement differs according to the criteria used for diagnosis. Therefore, more comprehensive criteria are required for the diagnosis of anterior disc displacement.