Extra- and Intramuscular Innervation of Masseter: Implications for Facial Reanimation

Irreversible facial paralysis results in significant functional impairment. Despite its clinical importance, there are few innervation studies of the masseteric nerve (MN). The purpose was to investigate the extra- and intramuscular innervation of masseter in 3D. The MN throughout its entire course was dissected, digitized and modeled in 8 formalin-embalmed cadaveric specimens (mean age 84.9±12.2years). The nerve was digitized at 1-2mm intervals using a Microscribe™ Digitizer and modeled in 3D in Autodesk® Maya®. Two or three extramuscular nerves were found to enter the deep head (DH) of masseter: one main MN (n=8) and one (n=4) or two (n=4) smaller primary nerve(s). The main MN supplied both the DH and SH, whereas the smaller primary nerve(s) only supplied the DH. Surgical landmarks for MN localization were quantified. Comprehensive mapping of the innervation of masseter throughout its volume revealed neural partitioning that could provide a basis for surgical planning and simulation.M.Sc