Nonparticipatory stiffness in the male perioral complex

Purpose: The objective of this study was to extend previous published findings in the authors' laboratory using a new automated technology to quantitatively characterize nonparticipatory perioral stiffness in healthy male adults. Method: Quantitative measures of perioral stiffness were sampled during a nonparticipatory task using a computer-controlled linear servo motor to impose a series of tensile displacements over a span of approximately 24 mm at the oral angle in 20 healthy young male adults. Perioral electromyograms were simultaneously sampled to confirm nonparticipation or passive muscle state. Perioral stiffness, derived as a quotient from resultant force (DF) and oral span (DX), was modeled with regression techniques and subsequently compared to previously reported perioral stiffness data for female adults. Results: Multilevel regression analysis revealed a significant quadratic relation between the perioral stiffness and interangle span; however, no significant difference was found between adult males and females. Conclusion: These normative measures will have application to future studies designed to objectively assess the effects of pathology (i.e., progressive neuromotor disease, traumatic brain insult) and intervention (pharmacologic, neurosurgical, and reconstructive surgery of the face [i.e., cleft lip, trauma, missile injuries]) on facial animation and speech kinematics.