Clinical anatomy of the superior labial branch of infraorbital nerve.

The infraorbital nerve (ION), a branch of the maxillary division of the trigeminal nerve, provides sensory innervation to the midface via its terminal divisions. Among these, the superior labial branch (SLb) supplies the upper lip and adjacent mucosa, regions frequently involved in oral, maxillofacial, and cosmetic procedures. Despite its clinical importance, the anatomy of the SLb has received relatively limited attention compared with other ION branches. This review synthesizes current evidence on the SLb’s course, branching patterns, innervation, morphometry, and variations, with emphasis on its relevance to surgical practice. Anatomical studies demonstrate that the SLb is the largest terminal division of the ION, often exhibiting medial and lateral subdivisions that anastomose with neighboring nerves. Its distribution predominantly follows a vertical orientation, supplying both cutaneous and mucosal structures of the upper lip. Variability in origin, branching, and accessory foramina underscores the need for careful surgical planning. Injury to the SLb is a recognized complication of Le Fort I osteotomy, midfacial trauma, and periapical procedures, potentially leading to long-term sensory disturbances. A comprehensive understanding of the SLb enhances intraoperative nerve preservation and may reduce postoperative morbidity, highlighting its significance for clinicians operating in the midfacial region. Key words: Anatomy, Cadaver, Trigeminal nerve, Oral and maxillofacial, Histology Received May 15, 2025; 1st Revised July 31, 2025; 2nd Revised September 26, 2025; 3rd Revised November 21, 2025; 4th Revised January 9, 2026; Accepted February 12, 2026 Anat Cell Biol Hiroaki Takakura, et al 2 www.acbjournal.org https://doi.org/10.5115/acb.25.150 diminished sensation in the infraorbital, lateral nasal, and upper lip regions [3]. Such sensory disturbances can affect a patient’s quality of life and postoperative recovery. While multiple studies have examined the anatomical variations and branching patterns of the ION [4], much of this research has focused on the main trunk and its major divisions. However, the distribution and detailed anatomy of the SLb of the ION