Lower lip displacement during in-vivo stimulation of human labial muscles

Abstract

Displacement was measured at the lower lip midline and the corner of the mouth during direct electrical stimulation of labial muscles. Trains of electrical stimuli were delivered through hooked-wire electrodes to produce tetanic contractions in depressor labii inferior, mentalis, orbicularis oris inferior and depressor anguli oris. Stimulation of mentalis moved the lip superiorly and anteriorly, and depressor labii inferior stimulation produced movement in the opposite direction. When stimulated at a lateral electrode placement, orbicularis oris inferior moved the midline of the lip superiorly and posteriorly. Stimulation of orbicularis oris inferior at the midline produced wrinkling of the skin in and around the vermilion of the lip. The major influence of depressor anguli oris stimulation was a large inferior movement at the corner of the mouth. The movements measured during stimulation were very similar to those observed previously during electromyographic activity of mentalis and depressor labii inferior ( Archs oral Biol. 23, 189–194).