Temporomandibular joint effects of activator treatment: a prospective longitudinal magnetic resonance imaging and clinical study.

The aim of this prospective longitudinal clinical and magnetic resonance imaging (MRI) study was to analyze the effect of Activator treatment on the disc-condyle complex and the posterior attachment of the temporomandibular joint (TMJ) considering the degree of compliance in the evaluation. The material was comprised of 30 class II, division I patients (nine girls and 21 boys) who underwent Activator treatment. The average pretreatment age of the subjects was 11.4 years. Parasagittal MRIs in closed mouth position from before and after one year of Activator treatment were analyzed metrically. Possible clinical and subclinical soft tissue lesions of the posterior attachment of the TMJ were assessed by passive joint loading before, after six months, and after one year of Activator treatment. The overjet was continuously documented as a clinical measure for treatment reaction. To assess patient compliance, the subjects had to perform daily wearing-time records. Furthermore, the Activator was clinically inspected for fitting accuracy and signs of wear. The results revealed the following: (1) during the one-year treatment period the sagittal dental arch relationship improved, but a class I occlusion could not be achieved in all patients; (2) on average, a physiologic position of disc, condyle, and fossa was present both before and after one year of Activator treatment; (3) a pretreatment physiologic disc-condyle relationship was unaffected by Activator therapy; 4) a pretreatment disc displacement could not be repositioned during Activator treatment; (5) the prevalence of a subclinical capsulitis of the inferior stratum of the posterior attachment increased during Activator treatment; and (6) the degree of compliance had no influence on the disc-condyle relationship or the reaction of the posterior attachment of the TMJ.