A single-subject finite element study on the influence of root dislocation direction on inferior alveolar nerve stress during mesially impacted mandibular third molar extraction.

BACKGROUND

Impacted mandibular third molars (M3Ms) often require extraction, with inferior alveolar nerve injury (IANI) as a serious complication. Preoperative risk stratification lacks biomechanical insight into nerve compression during tooth dislocation.

METHODS

Twelve mandibular models were constructed based on CBCT data, varying M3M root morphology (single/double), mandibular canal (MC)-M3M distance (d-close: 1-3 mm; d-intimate: <1 mm), and MC position (caudal/buccal/lingual). Stress distribution, maximum Von Mises stress (MVMS) at the MC interface, principal strain, and MC displacement were analyzed under buccal/mesial loading.

RESULTS

Under buccal loading, the MVMS range at the MC interface was 0.032-0.143 MPa, with the double-rooted model peaking at the lingual-intimate MC, while the single-rooted model had the lowest at the buccal-close MC. Stress concentrated at root apices; lingual MC showed higher stress than other positions. Mesial loading yielded lower MVMS (0.019-0.034 MPa), locally located near the mesial root, with stress at the buccal MC higher than at the lingual MC.

CONCLUSIONS

During the initial loading phase, mesial dislocation generated lower MC stress than buccal dislocation, suggesting it may be biomechanically safer at that moment. The lingual position of the MC exhibited high-risk characteristics under buccal loading. The proximity of the root to the canal and multi-root contact increased stress transmission, potentially elevating the risk of IANI. In such cases, sectioning the crown or root may reduce risk by simplifying complex contacts to more straightforward single-root interactions.