A cephalometric analysis of skeletal and dental changes contributing to Class II correction in activator treatment.

The purpose of this investigation was to evaluate cephalometrically the mechanism of anteroposterior occlusal changes in activator treatment. The analysis used made it possible to relate alterations in the occlusion to sagittal skeletal and dental changes in the maxilla and mandible. The sample consisted of thirty Class II, Division 1 malocclusion cases treated successfully with activators during an average time period of 32 months. Before- and after-treatment head films in centric occlusion were analyzed. The occlusal line (OL) and occlusal line perpendicular (OLp) through sella were used for reference. Linear measurements were performed parallel to OL. The following results were found: (1) The improvement in occlusal relationships in the molar and incisor segments was about equally a result of skeletal and dental changes. (2) Overjet correction averaging 5.0 mm was a result of 2.4 mm more mandibular growth than maxillary growth, a 2.5 mm distal movement of the maxillary incisors, and a 0.1 mm mesial movement of the mandibular incisors. (3) Class II molar correction averaging 5.1 mm was a result of 2.4 mm more mandibular growth than maxillary growth, a 0.4 mm distal movement of the maxillary molars, and a 2.3 mm mesial movement of the mandibular molars. (4) When the findings were compared with longitudinal records of persons with normal occlusion (Bolton standards), activator treatment seemed to inhibit maxillary growth, move the maxillary incisors and molars distally, and move the mandibular incisors and molars mesially. Mandibular growth appeared not to be affected by activator treatment.