Purpose: The purpose of this study was to determine the cause of injuries of the lower labial branches (LLB) of the mental nerve (MN) after biopsy of minor salivary glands (BMSG), labial nodule excision, or symphyseal bone procedures using a labial approach.
Patients and methods: Thirty-two MN were dissected in 16 cadavers to trace the labial branches. The following factors were recorded: 1) the number of LLB; 2) the angle between the medial LLB and the fibers of the orbicularis oris muscle; 3) the anastomoses between the lateral branches; and 4) the midline crossover innervation of the LLB. The number of branches on each side, as well as values of the angle between the nerves and superficial fibers of the orbicularis oris muscle, were compared using the Wilcoxon test.
Results: The mean number of LLB was 2 (SEM, 1; range, 1 to 4); the average angle between the medial LLB and the fibers of the orbicularis oris muscle was 36 degrees (SEM, 2 degrees ), without any statistical difference between the two sides (P = .78); an anastomosis between the 2 lateral branches of the LLB was observed in only 1 case; and the mean midline crossover innervation of the LLB was 25% (SEM, 14%) of the intercommisural distance. This crossover innervation was present only on the ventral surface of the lip.
Conclusions: These data suggest that injuries to the LLB could be prevented if the incision(s) are made horizontally on the dorsal aspect of the lower lip, and the angle between the incision and the long axis of the lip is approximately 36 degrees . In the case of symphyseal bone procedures using a labial route, a "U"-shaped incision parallel to the LLB is suggested.