Orthodontics, condylar position, and TMJ status.

T here are few more compelling issues in orthodontics than the relationship between orthodontic treatment and the status of the temporomandibular joint (TMJ). A focal point is the position of the condyle. Interest in calndylar position has been stimulated and reinforced possibly by two interrelated opinions concerning the cause of an internal derangement. One is that posterior condylar position within the fossa is associated with an anteriorly displaced disk.' Presumably, space constraints would require that the condyle be positioned posteriorly if the disk were anterior. For instance , Farrar and McCarty' indicated that a space of less than 2.4 mm between the posterior wall of the fossa and the posterior aspect of the condyle, noted on transcranial radiographs, was suggestive of an internal derangement. Further, they indicated that a predispos-ing factor to the development of an internal derange-ment is posterior positioning of the condyles. Others have noted that there is a wide range of variability in the condylar position in normal subjects .* ,4ccordingly, " A diagnosis of an internal de-rangement cannot be made on the basis of nonconcen-tric radiographic condylar position alone. " This may be one reason why in 1983 a consensus group believed that there was insufficient documentation to endorse the use of condylar position as a diagnostic sign of TMJ disorders .' However, there is some evidence to suggest that condyles more often are located posteriorly when there is a reducible dislocation of the disk (a reciprocal clicking situation). Under nomral conditions approximately 25% of the condyles in asymptomatic persons with Class I occlusions are positioned posteriorly in the fossa. When internal derangements were arthrograph-ically verified, Westesson' found that the condyles in 18/45 patients (40%) were posterior. Similarly, Ron-quill0 and associate@ determined that approximately 50% of the condyles were positioned posteriorly in patients with reducible dislocations of the disk. Accordingly , there may be an association between posterior condylar position and an internal derangement. More data are required to verify this relationship. Some critical questions remain unanswered. Is posterior positioning of the condyle associated with an internal derangement a cause of the dislocation of the disk, as suggested by some? " 7-9 Or does it occur secondarily after the disk becomes displaced because of the space limitations within the fossa? Until the patho-genesis of an internal derangement is described, these questions cannot be answered satisfactorily. The second opinion is that an iatrogenic cause of posterior condylar …