using panoramic radiography to evaluate internal derangement of temporomandibular joint

Introduction: Clinically images prescribed for diagnosis of TMJ problems are mostly related to the internal derangement (ID) and its consequences. It is of no doubt that MRI is the image modality of choice for such purpose. However, a cheap and easily available image option, such as the orthopantomogram (OPT), is still valuable especially used for screening, if its diagnostic power can be promoted. The value of OPT assisting in diagnosis of TMJ ID has been criticized. Its limitations might be attributed to projection distortion, lack of clearly defined criteria, and the fact that TMJ ID is not necessary to be associated with obvious bony changes. 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 occurred near lateral condylar pole, which is often clearly depicted on the OPT. The aim of this study was thus to explore a possible gain of diagnostic value of TMJ ID by assessing the cortex on the orthopantomogram.aterials & Methods: Both sagittal serial TMJ MR images and OPT of 117 female subjects (18 years to 28 years , mean age 22.19, SD 2.85) were used for this 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 a TMD specialist and a radiological technician. The 2 readers read the OPT with discussion to achieve an agreement on diagnosis, but blind to MRI gold standard. Since there’s no general consensus on norms of TMJ condyle shown on OPT, we defined normal condyle should be convexly round in shape and covered with thin and even-thickened cortex . If the condylar morphology was deviated from the norms, it was then diagnosed to have internal derangement . If the cortical bone near the lateral condylar pole was missing or became thickened, it would also be diagnosed to have internal derangement. The sensitivity and specificity of using OPT with different diagnostic criteria diagnosis to diagnose the existence of TMJ ID were then calculatedesults:9 TMJs were excluded from the analysis because severe overlapping of condyle to its surrounding bony structures. For the 198 TMJ, 57 were with normal disc/condyle relationship, 50 were with disk displacement with reduction (DDwR) and 88 were with disk displacement without reduction (DDw/oNR). By using condylar shape alone, only 48% were corrected diagnosed. The sensitivity and specificity were 30% and 95%, respectively. By considering the additional information of cortical bone, the correct diagnosis was still remained as 48%, the sensitivity slightly raised to 35%, but the specificity fell down to 84%. MRI indicated that 2 of the 50 DDwR TMJ and 67 of the 88 DDw/oR TMJ, their condyles were with obvious bony deformation. For those 69 TMJ with bony deformation, 78% can be revealed by using condylar shape alone (sensitivity and specificity were 50% and 92%). If the cortical bone was taken into consideration, 75% can be correctly diagnosed, the sensitivity became 56% and specificity was 84%.onclusion: ith the limitation of this study, the following conclusions might be drawn:. Only severe TMJ ID would be often associated with obvious bony changes. . Most of the condylar deformation can be revealed by the OPT. Therefore, OPT seems to be suitable only for screening severe TMJ ID. . TMJ showing cortical bone seems to be also have morphological changes. Therefore, the information of cortical changes don’t promote too much on diagnostic power.