New diagnostic criteria of TMJ internal derangement by using orthopantomogram

Objectives: The main limitation of using orthopantomogram (OPT) for screening TMJ internal derangement (ID) is that the distorted representation of TMJ is not faithfully enough for us to make a judgment, especially when the associated change is mild. It has been proposed that sequential structural changes, namely from erosion to re-cortication, might occur along with natural course of TMJ ID. Interestingly, such bony changes are frequently happened near lateral condylar pole, which is often clearly revealed on the OPT. The aim of this study was to explore a possible gain of diagnostic value of TMJ ID by assessing the cortical bone on the OPT. Materials and Methods: In this pilot study sagittal serial TMJ MRI and OPT of 10 subjects were used for analysis. The existence of TMJ ID of every single joint was diagnosed based on TMJ MRI by an experienced dentist. The reading of OPT was done by another dentist and a radiological technician together with discussion but blind to MRI diagnosis. From the OPT, every individual TMJ was diagnosed as normal or not according to deviation of morphology and the display of bony cortex near the lateral condylar pole. Sensitivity of specificity of diagnosis based on morphology and cortex condition were then calculated. Results: For the 20 TMJ, 14 were with ID and 6 were with normal disc/condyle relationship. The sensitivity/specificity of diagnosis based on morphology and cortex condition shown on the OPT were 0.36/1 and 0.5/1, respectively. Conclusion: TMJ ID is not always yield sufficient bony changes that can be depicted clearly on the orthopantomograms. However, it might augment the screening power of TMJ ID of the orthopantomograms by judging the cortex conditions near lateral condylar pole. Evaluation with larger sample size is needed to work-out clearer diagnostic guidelines.