Abstract
In this report, we discuss the relationship between the configuration of the disc, with/without reduction, the degree of displacement and the duration of displacement.
Time of appearance of joint noise and limitation of mouth opening were identified by reviewing the patients' history. Subjects were 105 TMJs (50 TMJs with disc displacement with reduction and 55 TMJs with disc displacement without reduction), of which the configuration of the disc could be detected by MRI.
Two coronal section and three sagittal section images of TMJ were taken by 1.5 Tesla Superconductive MRI. The configuration of the disc was classified into the following groups according to Westesson's criteria: 1. biconcave, 2. biplanar, 3. reversed, 4. biconvex, 5. enlargement of posterior band (EPB). Biconcave disc was regarded as normal, and the others were regarded as deformities of the disc. The degree of displacement was classified as: 1. small (the portion of the thick posterior band is in contact with the mandibular head), and 2. large (the thick posterior band is in front of the mandibular head).
Deformities of the discs were observed in all cases with disc displacement without reduction, and in 56.0% in cases with disc displacement with reduction. In 22 out of 105 TMJs whose configuration of the disc was normal, 20 TMJs showed disc displacement with reduction, and a small amount of displacement. Furthermore, 6 TMJs showed the normal disc configuration after more than 60 months of the development of anterior disc displacement. All 6 TMJs showed disc displacement with reduction, and 5 out of 6 TMJs showed a small amount of displacement. The results suggest that with/without reduction and the degree of displacement are more responsible for the deformity of the disc than the duration of disc displacement.
