A prospective study of Twin-block appliance therapy assessed by magnetic resonance imaging.

Forty children displaying Class II Division 1 malocclusion were involved in a prospective magnetic resonance image investigation to evaluate the effects of Twin-block functional appliances on the temporomandibular joints. None of these children had clinical signs or symptoms of temporomandibular disorders. Nineteen children were treated with a Clark Twin-block appliance for 6 months; the other 21 children received no treatment and served as controls. Comparison between control and Clark Twin-block groups suggested that reduction of the condylar axial angle represents a feature of untreated Class II growth patterns, whereas axial angle stability with Clark Twin-block therapy may suggest alteration of condylar growth direction. Condyles that were positioned at the crest of the articular eminence by the Clark Twin-block at the beginning of treatment had reseated back into the glenoid fossa after 6 months. However, 75% of the condyles were more anteriorly positioned in successfully treated Clark Twin-block cases. There was no clear evidence of remodeling of the glenoid fossa at the eminence as a result of Clark Twin-block treatment. The initial prevalence of disk displacements for the combined groups was 7.5% anterior, 5% medial, and 12.5% for lateral disk displacement. Clark Twin-block therapy had neither positive nor negative effects on disk position, and there was no convincing evidence that the disk was recaptured.