The mandibular plane angle in activator treatment.

The long-term results of activator treatment were investigated in 15 subjects with a small and 13 subject with a large pretreatment mandibular plane angle. The results of the investigation revealed the following: 1. Activator treatment resulted in a general improvement in the sagittal and vertical incisor relationship in both large and small angle cases. 2. Overjet relapse was more frequent and overbite relapse less frequent in large angle cases than in small angle cases. 3. During the period before treatment follow-up examination the frequency of patients with open bite increased in the large angle group and decreased in the small angle group. 4. The mandibular intercanine arch width was smaller and the frequency of crowding in the mandibular incisor segment was higher in the large angle group than in the small angle group. 5. A large pretreatment mandibular plane angle, per se, was not a primary factor in treatment failure. However, an unfavourable mandibular growth in combination with an atypical tongue function seemed to be the main reason for the relapse found in the large angle subjects.