Three-dimensional Observation of the Mandible and Accessory Mental Nerve Using Sihler’s Staining Technique
It is generally known that there are two mental foramina and two mandibular foramina. It is also known that occasionally there are some accessory foramina in the mandible, including lingual, buccal, retromolar, and accessory mental foramina. Among these accessory foramina, the accessory mental foramen in particular is located in a dangerous area for the oral surgeon1).The reported incidence of an accessory mental foramen ranges from 2.0% to 11.9%. We can easily diagnose accessory mental foramina using three-dimensional computed tomography (3D-CT). However, it is sometimes difficult to diagnose the accessory mental foramina using panoramic findings alone2). There are few reports of accessory mental nerves branching off the accessory mental foramina.In this study, we investigated the distribution patterns of the accessory mental nerve using Sihler’s staining and transparency technique and 3D-CT images. We were able to observe the relations among the mandible and the accessory mental foramen and the accessory mental nerve
Materials and methods
In 2012 in our laboratory, a gross anatomical dissection class discovered a human mandible with a right accessory mental foramen and an accessory mental nerve. We recorded the size, position, and distance between the mental foramen and the accessory mental foramen. To create mandibular transparency, the mandible was decalcified using 10% ethylenediaminetetraacetic acid and was preserved in glycerin. We performed Sihler’s staining technique for skin of the inferior labial and mental region of this mandible to stain nerve fibers. Sihler’s technique stains nerve fibers deep blue using Ehrlich’s hematoxylin. The other soft tissues become transparent. Thus, it clarifies the 3D relations between the mandible and the accessory mental nerve and accessory mental foramen.
Results
Foramen morphology
The left mental foramen was positioned in the longitudinal axis of the second premolar. The distance from the base of the mandible was 11.2 mm, and its diameter was 3.2 mm. The right mental foramen was positioned in the longitudinal axis of the second premolar. The distance from the base of the mandible was 14.8 mm, and its diameter was 2.6 mm. The right accessory mental foramen was positioned between the second premolar and the first molar at a distance of 6.2 mm posteroinferiorly from the right mental foramen. The distance from the base of the mandible was 11.2 mm, and its diameter was 1.8 mm.
Mental nerve and accessory mental nerve
The right accessory mental nerve mainly distributed to the right angular region. The right mental nerve mainly distributed to the right inferior labial and mental regions. The width of the right mental nerve was 1.8 mm, and that of the right accessory mental nerve was 0.9 mm. The left mental nerve (2.3 mm) distributed to the left angular, inferior labial, and mental regions.
Conclusion
The branches of the mental nerve from the mental foramen can be classified into three groups: angular branch, inferior labial branch, and mental branch. In our study, Sihler’s staining technique revealed that the accessory mental nerve was a branch to the angular region. We also visualized the 3D relations among the mandible, the accessory mental foramen, and the accessory mental nerve. These results will be useful clinically to avoid neurovascular complications during implant surgery, nerve block, and other oral surgery procedures.
Refferences
1) Seema Patil, et al: Accesory mandibular foramin: a CT study of 300 cases. Surg Radiol Anat 35:323-330,2013.
2) Sudhindra Kulkarni, et al: Accidental identification of accessory mental nerve and foramen during implant surgery. J indian Soc Periodontol 15:70-73,2011.