Muscle activity in Class II, Division 1 malocclusions treated by bite jumping with the Herbst appliance: An electromyographic study

Abstract

The effect of continuous bite jumping on masticatory muscle activity was investigated in ten growing boys with Class II, Division 1 malocclusion treated with the Herbst appliance. Integrated EMG recordings from the temporal and masseter muscles were analyzed quantitatively during maximal biting in intercuspal position and during chewing of peanuts. The results of the investigation revealed the following: (1) Before treatment the EMG activity from the masseter muscle was less than from the temporal muscle, especially during maximal biting in the intercuspal position. After treatment no difference in EMG activity was found between the two muscles, during either maximal biting or chewing. (2) During insertion of the Herbst appliance, the mandible was jumped anteriorly to an incisor edge-to-edge position with no occlusal contacts present in the posterior dental arch segments. The EMG activity from the two muscles during maximal biting and chewing was markedly reduced. (3) When the Herbst appliance was removed after 6 months of treatment, normal occlusal relations were found in all patients. The EMG activity in the two muscles exceeded pretreatment values. The increase in EMG activity seen was greater for the masseter than for the temporal muscle. The results of this investigation suggest that the increased muscle activity seen in the Class II, Division 1 cases during bite jumping with the Herbst appliance was due to an altered sagittal jaw base or dental relationship.