Mandibular lateral translation during symmetric mandibular function in relation to patterns of intracapsular derangement of TMJ

PURPOSE: The purposes of this study were to examine the occurrence of different types of mandibular lateral translation (ΔYMLT) using condylography and magnetic resonance imaging (MRI), to investigate the relationship between ΔYMLT and the disunion pattern in intracapsular derangement patients with ΔYMLT, and to consider the three-dimensional therapeutic position of the condyle in the mandibular fossa. MATERIAL AND METHODS: Sixty-two patients with ΔYMLT, or side shift, during symmetrical mandibular movements were analyzed with computerized condylography and MRI to determine the occurrence of different types of MLT and the relationship between the ΔYMLT and the intracapsular derangement pattern. RESULTS: Of a total of 62 subjects, we classified 43 (69.4%), 12 (9.4%), and 7 (11.2%) of them as ΔYMLT type, closed lock type, and excessive condylar rotation type, respectively. There was a high prevalence of ΔYMLT for subjects who had one side antero-medial (including medial sideway) and the other side antero-lateral disk displacement. The directions of ΔYMLT and disk displacement coincided in 95.3% of cases; this means recapturing of the displaced disk by the condyle in lower joint translation. CONCLUSION: Results indicate that mandibular lateral displacement causes the condyle to be displaced in the same direction, and the disk displacement to the opposite side; hence it creates ΔYMLT in the disk displacement direction. On the basis of these findings, it is concluded that the ΔYMLT is a useful indicator for early detection of intracapsular derangement and that the ΔYMLT allows estimation of the therapeutic condylar position.