Skeletal profile changes related to two patterns of activator effects.

A longitudinal cephalometric study was carried out on twelve boys and thirteen girls who initially exhibited Class II, Division 1 malocclusion and who were treated exclusively with activators. Twenty-four boys and fifteen girls, corresponding with the experimental subjects with respect to initial age and observation period, were selected as controls. The aim of the investigation was to examine cephalometric profile changes associated with two patterns of effects of activator treatment detected previously. The findings demonstrate that the two types of reaction bring about similar corrections of both apical base discrepancy and dental Class II relationship but clearly differ in their effects on the skeletal profile. Whereas the first type of reaction results in an improvement in mandibular retrognathism, a marked rotation of the occlusal plane, and good vertical control of the upper and lower dental arches, the second type is distinguished by a significant reduction of maxillary prognathism, downward and backward rotation of the mandible, and forward tipping of the lower incisors. Additional evidence presented further suggests that the two patterns of effects are due to differences in the construction bites of the appliances. According to this hypothesis, a great interocclusal height of an activator would lead to the first and a low construction bite to the second type of reaction.