An Electromyographic Analysis of Masticatory Muscle Imbalance with Relation to Skeletal Growth in Dogs

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Abstract
The functional activity of the temporal muscle in dogs was analyzed under normal conditions and under conditions of muscle imbalance. Once chewing was voluntarily initiated in the controls, the subsequent reflex chewing was unilateral. The biting force was asymmetrical and greater on the side where the food was located. Various conditions of muscle imbalance were created by the removal of the other temporal muscle and/or one or both masseter muscles in different combinations. Unilateral action of the temporal muscle was superseded by a bilateral action in all but 1 preparation. When both masseter muscles were removed, the action of the temporal muscle remained unilateral. The effects of the various muscle imbalances on the development of the cranio-facial skeleton were slight and localized to areas of muscle origin and insertion. More general changes in morphology occurred only when both masseters and 1 temporal were removed.