Intraoral Observation of the Mentalis and Incisivus Labii Inferioris Muscles.

The mentalis (MT) and the incisivus labii inferioris (ILI), which are accessory muscles of the orbicularis oris (OO) muscle, form an intertwined and three-dimensionally related complex. The purpose of this study is to clarify the relationship between the MT, ILI, and OO muscles via intraoral dissection. Twenty-two sides from 11 fresh adult Caucasian cadaveric heads were used, and the MT, ILI, and OO dissected under the surgical microscope. Next, measurements of the bony attachment were carried out on another 12 sides. The fibers of the MT were separated into 2 parts: a superior and an inferior part with the former coursing anteromedially and joining the inferior part of the OO. The latter coursed anteroinferiorly to the skin of the chin. The ILI traveled anterolaterally and joined the inferior part of the OO. Inferior labial branches of the mental nerves ran on the OO. There was a significant difference (P = 0.0001) between specimens that were edentulous or had severe periodontitis with regard to the distance from the alveolar ridge to the upper side of the quadrangle when compared with specimens with mild periodontitis. However, there was no significant difference (P > 0.05) between specimens that were edentulous or had severe periodontitis specimens with mild periodontitis with regard to the distance from the inferior border of the mandible to the lower side of the quadrangle. We believe that the observations of this study could help surgeons better understand the anatomy of the chin and minimize complications following surgical and other invasive procedures in this area.