Accessory Mandibular Foramina: An Anatomical Study in Dry Mandibles Along with Meta-Analysis

Background/Objectives: The accessory mandibular foramina (AMaFs) are small openings in the mandible that have been proposed to play a significant role in clinical practice. The objective of the present study was to examine the number, diameter, and distance of AMaFs to mandibular foramen in dry mandibles and to meta-analyze all available data after a systematic review, aiming to address gaps regarding the AMaFs potential clinical impact. Methods: We assessed the number, diameter, and spatial relationship of AMaFs to the mandibular foramen in human adult dry mandibles of unknown gender and age derived from our Laboratory. Stainless steel wire threads and digimatic caliper measurements were utilized by two separate raters. Cluster analysis was employed for the classification of foramina into distinct spatial groups. Furthermore, following the PRISMA guidelines, we conducted an unlimited literature search using the terms “accessory mandibular” and “foramen/foramina” across the PubMed, Scopus, SciELO, and Google Scholar databases to identify all published studies that reported on the prevalence and morphology of AMaFs in dry mandibles or cadaveric material. Radiological studies were excluded. The search was completed on July 13, 2025. Study quality was evaluated using the appropriate AQUA tool. Data synthesis was carried out using STATA 19. No external funding was received. Results: A total of 96 dry mandibles (50 dentate and 46 edentulous) were analyzed. AMaFs were detected in 8 / 96 mandibles (8.3 %). In these mandibles, a total of 25 accessory mandibular foramina, all superior to the mandibular foramen, were recognized (mean: 3.13 foramina / mandible) with a mean diameter 0.56 ± 0.10 mm, and a mean distance from the mandibular foramen 11.34 ± 1.29 mm (mean vertical distance: 10.32 ± 1.35 mm and mean absolute horizontal distance: 3.78 ± 0.49 mm). Of these foramina, 21 / 25 (84 %) had a diameter of ≥0.5 mm; their number, diameters, and distances from the mandibular foramen was comparable between left and right hemimandibles. Based on their positioning to the mandibular foramen, the AMaFs were classified into two distinct groups (clusters). Furthermore, a total of 36 studies were included in the meta-analysis. In most of the mandibles (65.1%; 95% CI: 57.7 – 72.2%; I2: 94.9%), no AMaF was detected. Unilateral presence of one or more AMaFs was observed in 20.9% of mandibles (95% CI: 16.3 – 25.9%; I2: 91.3%), while bilateral occurrence was identified in 10.6% (95% CI: 6.9 – 15.0%; I2: 93.0%). Additionally, 2.4% of mandibles (95% CI: 1.0 – 4.2%; I2: 86.3%) exhibited multiple AMaFs (≥2) on at least one side. On average, each hemimandible contained 0.253 AMaFs (95% CI: 0.198 – 0.312; I2: 96.9%). The overall mean diameter of AMaFs was estimated at 0.65 ± 0.33 mm. The substantial heterogeneity observed was not attributed to publication bias. Conclusions: AMaFs are detected in one third of the mandibles. The AMaFs are typically located superior to the mandibular foramen, on the anterior or posterior aspect of the mandible, and may provide additional entry routes for nerve fibers. Failure to recognize these anatomical variations usually lead to incomplete anesthesia or persistent pain in specific regions of the lower jaw during routine dental procedures. Clinicians should remain aware of these variations and adjust their surgical or anesthetic techniques accordingly to ensure effective and comprehensive anesthesia.