Pancherz, H. Anehus, M. Masticatory function after activator treatment. An analysis of masticatory efficiency, occlusal contact conditions and EMG activity.Masticatory function was investigated in nine patients with relapse and ten patients without relapse of overjet after activator treatment, Masticatory efficiency, evaluated by a chewing test, was related to the number of intermaxillary tooth contacts and the electromyographic (EMG) activity from the temporal and masseter muscles during chewing. The results of the investigation indicated that a reduced masticatory efficiency was connected with fewer intermaxillary tooth contacts and less EMG activity from the temporal and masseter muscles. In patients with relapse of overjet, masticatory efficiency and muscle activity was reduced in comparison with patients without relapse. The relationship between the number of tooth contacts and masticatory efficiency was poor in the relapse patients. Unstable occlusal conditions and atypical tongue function may be an explanation.