After review of the literature, there appears to be no report on the histology of the mandibular nerve fiber distribution. Therefore, using a Wistar rat model, immunohistochemical staining with protein gene product (PGP) and calcitonin gene-related peptide (CGRP) antibody for all nerves and only the pain-sensitive nerves, respectively, was performed. We also statistically compared the nerve distribution density by mandibular region. The section of the mandible from the alveolar crest to the mandibular canal was compartmentalized to several regions. Subsequently, nerve distribution density by region was measured microscopically in both the PGP- and CGRP-positive nerves. Furthermore, the ratio of CGRP- to PGP-positive nerves was measured in each region and statistically compared. In both the PGP- and CGRP-positive nerves, the nerve distribution density significantly increased vertically toward the mandibular canal from the alveolar crest and horizontally toward the periodontal ligament from the periosteum. From the CGRP- to PGP-positive nerve ratio, the pain-sensitive nerve accounted for approximately >70% in each region. Pain would therefore be more likely to develop when surgical invasiveness deepens toward the mandibular canal or periodontal ligament. Therefore, sufficient local anesthetic infiltration and/or combined use of conduction anesthesia or periodontal ligament injection may be required. These results may aid in the development of more effective surgical and anesthetic techniques for mandibular surgery.