An electromyographic study on functional adaptations--associated with herbst appliance

Abstract

The purpose of this study was to examine functional muscular adaptation to changes in sagittal jaw relation by electromyography. The structural changes were induced by the Herbst appliance. The subjects consisted of four patients with Angle Class II Division 1 malocclusion. The structural changes were evaluated by lateral cephalograms. Functional muscular adaptation was evaluated by electromyogram (EMG) of masticatory muscles, including the inferior head of the lateral pterygoid (ILpt) muscle. The EMG of the ILpt muscle was recorded by using an intraoral surface electrode. The same pattern of cephalometric changes was observed in all patients. The ILpt muscle activity increased immediately after wearing the appliance just like when the construction bite position was taken. However, it reduced remarkably after 4 to 6 months in all patients. On the other hand, the superimposed cephalometric tracings indicated that the locations of the condyles related to the glenoid fossae were still more anteroinferior than their original positions 4 to 6 months after wearing the appliances in three patients. These findings seem to indicate multifactorial effects on the adaptation of the muscle function. It was concluded that functional adaptation to the newly-created morphological changes were not dependent only on the intensity and the duration of the functional stimulation.