Proposed graphical system of evaluating disc-condyle displacements of the temporomandibular joint in MRI

The aim of this preliminary study was to standardize the reading of magnetic resonance imaging (MRI) of the temporomandibular joint (TMJ). The MRI was conducted on a control group of eight subjects. In this study, the analysis of joint relationships was limited to the oblique sagittal plane, during the movement of controlled opening. The sections were analyzed by a computer-assisted quantitative method of graphical evaluation. The total surface area (TS) of the disc section was divided into an anterior surface area (AS) and a posterior area (PA), in accordance with a line joining the center of the condyle (C) to the center of the articular tubercle of the temporal bone (T). The disc-condyle relationships in the chosen plane of section were evaluated by the AS/TS ratio. If TS remains relatively constant, the AS/TS values on average decrease from 0.5 to 0.3 between the closed mouth position and the 25 mm open position. The results show good intra-observer reproducibility (p=0.26), evaluated by Wilcoxon's test. In conclusion, this protocol enables the displacement of the disc-condyle assembly during mouth opening to be described. Observed on a larger sample, the AS/TS would be able to show a range of variability in functional disc positions.