MOUTH RELAXED CONTRACTION OF RISORIUS
The lower lip in the relaxed open mouth looks thicker, but is not curled out from face. Only tips of the lower teeth are exposed. In risorius contraction, a full row of lower teeth are exposed, but the lips are stretched and the mouth widens. Depressor labii inferioris, by contrast exposes lower teeth down to the roots, creates deep overhang under the lip, and doesn't stretch or tighten the lip.
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