Iatrogenic risk and anatomical variability of the mandibular canal

The immediate proximity between the mandibular canal (MC) and the apices of the mandibular molars places the inferior alveolar nerve at the heart of concerns during endodontic or surgical treatments. Perforation or overfilling can lead to severe complications: paresthesia, chronic pain, or severe hemorrhages. While sexual dimorphism and ethnic variations in craniofacial anatomy are documented, practitioners often rely on generic data that do not necessarily reflect the clinical reality of specific populations.

This quantitative cross-sectional study aimed to precisely characterize the morphology and morphometry of the MC within a South African Black population. The objective was to evaluate, via CBCT scan analysis, the prevalence of critical structures such as anterior loops and bifid canals, while measuring the distances separating the MC from the root apices and cortical plates. Conducted on 30 mandibles (15 men and 15 women), representing 60 hemi-mandibles, the study tested the hypothesis of a significant difference in these measurements between sexes in this specific cohort, in order to refine preoperative planning at the dental practice.

Study methodology

For this cross-sectional quantitative study, researchers analyzed the mandibular anatomy of 30 Black South African patients (15 men and 15 women), representing a total of 60 hemimandibles observed bilaterally. Selection focused on adult subjects who imperatively presented their first and second mandibular molars.

The exclusion protocol was rigorous: any record with a history of dental surgery, trauma, fracture, or bone pathology was discarded to ensure the integrity of the anatomical measurements. The analysis relied on high-resolution CBCT imaging to map the course of the mandibular canal (MC) along two main axes:

• Morphological analysis (sagittal view): systematic search for anatomical variations such as anterior loops or bifid canals.
• Morphometric analysis (coronal view): precise measurement of the distance between the root apices (mesial and distal) and the upper border of the MC.
• Spatial positioning: evaluation of the distances separating the canal from the lingual and buccal cortical plates.

Each measurement was performed after aligning the planes with the long axis of the dental root to eliminate visual bias. The data were then subjected to statistical analysis to compare measurements between genders and evaluate bilateral symmetry.

Results of morphometric and morphological analysis

The study conducted on 60 hemimandibles (30 individuals) by CBCT analysis reveals significant anatomical variations and critical proximities between the mandibular canal (MC) and dental or cortical structures.

Qualitative anatomical variations

Analysis of the sagittal sections identified two major morphological variants within this sample of the black South African population:

• Anterior loops: Present in 11.67% of cases.
• Bifid mandibular canals: Identified in 5% of cases.

Distances between root apices and the mandibular canal

The proximity between the roots of the molars and the superior border of the MC is inversely proportional to the position of the tooth in the arch. The second molars show a significantly more marked proximity than the first molars.

Positioning in relation to cortical plates

The course of the mandibular canal shows a progressive displacement from the lingual wall towards the buccal wall from back to front:

• Lingual cortical plate: The average distance is shortest at the second molar (1.40 – 1.91 mm) compared to the first molar (1.75 – 2.84 mm).
• Buccal cortical plate: Conversely, the canal moves away from the buccal cortex at the second molar level (5.21 – 5.75 mm) compared to the first molar (3.14 – 4.97 mm).

Statistical analyses and sexual dimorphism

The application of the Mann-Whitney U test and linear mixed-effects models (LMM) revealed no statistically significant difference (p > 0.05) between males and females for all morphometric measurements performed. Although individual variations exist, sex does not appear to be a predictive factor for the position of the canal in this sample. The authors emphasize, however, that the limited statistical power of the study (n=30) requires caution in generalizing the absence of sexual dimorphism to the entire black South African population.

Anatomical risk analysis and clinical implications

The results of this study highlight an increased vulnerability during interventions on the mandibular second molar. With a reduced mean apex-to-canal distance (2.37 to 3.62 mm) compared to the first molar (> 5.45 mm), the risk of perforation or compression of the inferior alveolar nerve (IAN) due to filling material extrusion is clinically tangible. The study also confirms a preferentially lingual position of the canal (1.40 to 2.84 mm from the inner table), a major risk factor for implant surgery or the extraction of impacted teeth.

Morphological variations and study limitations

The identification of anterior loops in 11.67% of cases and bifid canals in 5% of cases highlights that "atypical" variations are frequent enough to compromise the success of a nerve block or cause intraoperative complications. Although no significant difference was observed between genders, the authors urge caution: the limited statistical power of the sample (n=30) does not yet allow for these data to be generalized to the entire South African Black population.

Implications for daily practice

In the practice, these data serve as a reminder that root morphology and the IAN pathway are highly individual. The absence of marked sexual dimorphism in this sample reinforces the idea that patient profile cannot be relied upon to anticipate a safety distance. Systematic use of CBCT is essential here as the only precision tool to identify critical structures, secure the endodontic procedure, and prevent irreversible neurosensory sequelae.

Summary of results

This CBCT analysis conducted on 60 hemimandibles reveals the presence of anterior loops in 11.67% of cases and bifid canals in 5%. Root proximity intensifies distally: the average distance between the apex and the mandibular canal drops from 6.08 mm for the first molar to only 2.99 mm for the second molar, with no significant distinction between sexes.

In concrete terms, for the practitioner:

• Critical vigilance on the second molar: The immediate proximity of the canal (descending to 2.37 mm) requires rigorous management of the working length in endodontics to avoid any sealer extrusion or iatrogenic nerve injury.
• Anticipate anatomical variations: With more than one in ten patients presenting an anterior loop, a preoperative CBCT examination is essential before any implant placement or apical surgery in the premolar/molar area.
• Canal trajectory: Keep in mind that the canal preferentially runs close to the lingual cortex at the molar level (1.40–2.84 mm) before migrating towards the buccal cortex in the direction of the mental foramen.

Technical lexicon of the study

Mandibular canal (MC): Bilateral bony conduit housing the inferior alveolar neurovascular bundle. Its oblique trajectory, from the mandibular foramen to the mental foramen, defines the critical safety limit for any endodontic or surgical procedure.

Anterior loop: Mesial extension of the inferior alveolar nerve beyond the mental foramen. Present in 11.67% of the cases studied, it constitutes a major danger zone for implant placement and premolar apical surgery.

Bifid canal: Anatomical division of the mandibular canal into two distinct branches. This variation affects 5% of subjects and requires increased vigilance during third molar extractions to avoid hemorrhage or sensory disturbances.

CBCT (Cone Beam Computed Tomography): 3D volumetric imaging allowing precise reconstruction of mandibular structures. The study demonstrates its necessity for measuring real distances between apex and canal and identifying morphological variations undetectable in 2D.

Lingual cortical plate: Inner wall of the mandibular bone. Measurements reveal close proximity to the canal at the level of the second molar (minimum distance of 1.40 mm), which increases the risk of cortical perforation during instrumentation.

Mental foramen (MF): Terminal orifice of the mandibular canal. Its precise localization ensures the success of nerve blocks and prevents iatrogenic trauma during access to premolar roots.

Information intended for healthcare professionals. This content may contain errors or truncated summaries. We recommend always verifying with the original source article. Delynov disclaims all responsibility regarding the use of this information. This document is not intended for patients or the general public.