The Positional Relationship Between the Mandibular Canal and the Lower Third Molar Determined on Cone-Beam Computed Tomography

Abstract

Background and Objectives: The extraction of mandibular third molars poses challenges due to their proximity to the mandibular canal and risk of inferior alveolar nerve (IAN) injury. Accurate preoperative evaluation is essential to minimize complications. This study assessed the three-dimensional positional relationship between the mandibular canal and lower third molars using cone-beam computed tomography (CBCT), aiming to identify anatomical positions associated with increased surgical risk. Materials and Methods: This retrospective study analyzed 253 CBCT scans of fully developed lower third molars. The mandibular canal position was classified as apical (Class I), buccal (Class II), lingual (Class III), or interradicular (Class IV). Contact was categorized as no contact, contact with a complete or defective white line, or canal penetration. In no-contact cases, the apex-canal distance was measured. Statistical analysis included descriptive and contingency analyses using the Chi-Square Likelihood Ratio test. Results: Class I was most common (70.8%) and presented the lowest risk, while Classes III and IV showed significantly higher frequencies of canal contact or penetration. Class II exhibited shorter distances even in no-contact cases, suggesting residual risk. Statistically significant associations were found between canal position and both contact type (p < 0.001) and apex-canal distance (p = 0.046). Conclusions: CBCT offers valuable insight into the anatomical relationship between third molars and the mandibular canal. High-risk positions-particularly lingual and interradicular-require careful assessment. Even in the absence of contact, close proximity may pose a risk and should inform surgical planning.

Keywords: CBCT; mandibular canal; third molar.

Figure 1

CBCT images illustrating the positional relationship of the mandibular canal relative to the mandibular third molar, classified into four types: (A) class I—apical position; (B) class II—buccal position; (C) class III—lingual position; (D) class IV—between the roots. Red arrows indicate the mandibular canal.

Figure 2

CBCT images demonstrating different contact relationships between the mandibular third molar and the mandibular canal: (A) No contact; (B) Contact with a complete white line; (C) Contact with a defective white line; (D) Penetration of the mandibular canal. Red arrows indicate the mandibular canal.

Figure 3

Distribution of ages of participants by gender; men are represented in blue and women in red.

Figure 4

Distribution of cases by distance criterion.

Figure 5

Distribution of cases from different types of contact according to the position of the mandibular canal.

Figure 6

Distribution of cases from different distance ranges according to the position of the mandibular canal.