Objectives: To determine whether disc displacement (DD) can be a factor causing changes in condylar position in the glenoid fossa, using limited cone beam CT (LCBCT) images taken in the same time period as MRI that verified DD.
Methods: The study included 60 joints in 57 male and female subjects aged 12-20 years (mean age 14.8 years). Subjects fulfilling the inclusion criteria were enrolled from a pool of post-orthodontic patients, and divided into four groups according to their disc status confirmed by MRI: partial DD (PDD), total DD with reduction (TDDWR), lateral DD (LDD) and medial DD (MDD). Changes in joint space from previously reported norms were measured on LCBCT images.
Results: In PDD, the condyles were displaced posteriorly in the fossae with a mean anterior space of 2.7 ± 0.5 mm (normal 1.3 ± 0.2 mm) and a posterior space of 1.8 ± 0.4 mm (normal 2.1 ± 0.3 mm). In TDDWR, the condyles were displaced not only posteriorly as observed in PDD, but also vertically with a reduced superior space of 1.9 ± 0.4 mm (normal 2.5 ± 0.5 mm). In LDD, the lateral space was significantly increased to 2.5 ± 0.3 mm (normal 1.8 ± 0.4 mm), while central and medial spaces were significantly decreased to 2.2 ± 0.5 mm (normal 2.7 ± 0.5 mm) and 1.7 ± 0.4 mm (normal 2.4 ± 0.5 mm), respectively. In MDD, the medial space was increased and the lateral and central spaces were significantly decreased.
Conclusions: These results indicate that DD in adolescents and young adults can cause the condyle to change its position in the fossa with alterations in joint space which depend on the direction and extent of DD.