The action of three types of functional appliances on the activity of the masticatory muscles.

Three commonly used functional appliances; namely, the Herbst, Frankel, and a simulation of the Clark twin block appliances were used to test the lateral pterygoid muscle hypothesis. This hypothesis states that postural and functional activity of the superior and inferior heads of the lateral pterygoid muscle increases after the insertion of a functional appliance. This increased activity, especially in the superior head of the lateral pterygoid muscle then acts to stimulate increased condylar growth.