Negative Impact of Synkinetic Mentalis Muscle on Smile Quality: Pathomechanism and Treatment with Mentalis-Targeted Selective Neurectomies.

Abstract

Background: The treatment of postparetic facial synkinesis is based on a combination of nonsurgical and surgical strategies. Improvements toward the restoration of a natural smile have been obtained with selective neurectomies and depressor anguli oris myectomy, but the lower lip frequently remains asymmetric and cranially displaced. The aim of this study was to evaluate the effect of the mentalis muscle on the position and symmetry of the lower lip in patients with synkinesis and to assess the added benefit of neurectomies of nerves innervating the mentalis muscle in improving the lower lip configuration and mandibular teeth show.

Methods: A retrospective cohort study of all patients with postparetic synkinesis was performed at the authors' institution. A nonmentalis neurectomy group including 12 patients treated with selective neurectomies without targeting the branches to mentalis muscle was compared with a mentalis neurectomy group including 16 patients who underwent additional specific mentalis branches neurectomies. All patients underwent depressor anguli oris myectomy. Analyses of standardized images were performed with ImageJ software.

Results: Postoperative comparisons between the 2 groups showed superior and significant improvements in the mentalis neurectomy group across all measures, including lower and upper border deviation ( P = 0.035 and P = 0.004, respectively), inclination of the lower lip ( P = 0.019), and lower quadrant dental show ( P = 0.004).

Conclusion: The addition of targeted selective neurectomies to the branches innervating the mentalis muscle significantly improved dental show and caudal position and symmetry of the lower lip during open-mouth smile.

Clinical question/level of evidence: Therapeutic, III.