Detection and Characterization of Anterior Loop, Accessory Mental Foramen, and Lateral Lingual Foramen by Using Cone Beam Computed Tomography

J Prosthet Dent. 2019 Nov 28;S0022-3913(19)30494-9. doi: 10.1016/j.prosdent.2019.06.026. Online ahead of print.


Statement of problem: The presence of an anterior loop (AL), accessory mental foramen (AMF), or lateral lingual foramen (LLF) adds complexity to the mental foraminal region, and consequently, implant placement in this region can damage the nerves and blood vessels if the structures are not carefully identified.

Purpose: The purpose of this retrospective study was to evaluate the characteristics of the AL, AMF, and LLF to provide recommendations for surgeons operating in the mandibular mental foraminal region.

Material and methods: Reconstructed cone beam computed tomography (CBCT) images in 306 Southern Chinese patients were retrospectively analyzed. The prevalence of the anterior loop was assessed, and the anterior loop length (ALL) was measured from the most anterior point of the mental foramen to the most mesial part of the anterior loop. The prevalence, location of the AMF as related to the mental foramen, and adjacent teeth were analyzed. Additionally, the distance from the mental foramen to AMF centers were measured. The prevalence, diameter, and location of the LLF were evaluated. The chi-square test was used for prevalence analysis (α=.05).

Results: Anterior loops were identified in 67.8% of the 612 hemimandibles, with a mean length of 3.3 ±1.2 mm, ranging from 1.2 to 7.3 mm. A total of 5.56% of the hemimandibles had an ALL ≥5 mm, and male patients had a statistically longer loop length (P=.006). The ALL on the right side was found to be statistically longer than that on the left side (P=.002). No statistically significant differences in the ALL were found among different age groups (P=.124). AMFs were observed in 10.5% of the patients, with most located in the posterosuperior position of the mental foramen. The mean distance between the center of the AMF and the mental foramen was 5.1 ±1.4 mm. LLFs presented in 69.9% of patients, with 74.0% located in the premolar region. The mean vertical diameter of the LLF was 0.9 ±0.3 mm, and the mean distance from LLF to the mandibular inferior border was 7.1 ±1.9 mm.

Conclusions: This study revealed that ALs, AMFs, and LLFs occurred often in the Southern Chinese population. Identifying the presence of the AL, AMF, and LLF is important before surgery in the mental foraminal region.