Relapse after activator treatment: A biometric, cephalometric, and electromyographic study of subjects with and without relapse of overjet

Abstract

R elapse of overjet and overbite is a common finding after treatment of Class II, Division 1 malocclusion. Relapse has been reported especially after fixed appliance treatment.l-g After activator treatment relapse was found by Pancherzl” and Dass,*’ while Ahlgren I2 found no relapse in his material. Improper treatment methods, insufficient retention, and unfavorable growth changes after treatment are certainly factors of importance but they could not totally explain the occurrence of relapses. Goldstein’ proposed an inherent morphogenetie pattern which limited the extent of treatment. If tooth movement was more extensive than the pattern could sustain, relapse would follow. Horowitz and Hixon13 pointed out that the dentition changed constantly throughout life and that orthodontic treatment could interfere with this normal developmental process. Relapse after treatment might thus be considered a physiological recovery toward the patient’s original condition. Herzberg4 found that. an unfavorable growth of the mandible after treatment, especially when combined with tonguethrust swallowing, was the main reason for Class II relapse. Pancherz’O measured the electromyographic (EMG) activity from the mentalis muscle in nine patients with and in ten patients without relapse of overjet after activator treatment. The results revealed a greater EMG activity in patients with relapse. Pancherz’O also found that the frequency of clinical registered tongue thrust was higher in the patients with relapse than in the patients without relapse. The aim of the present investigation was to examine patients with and with-