Fracture threshold of tooth roots and stress analysis of surrounding tissue during the extraction of impacted mandibular third molars using dental elevators.

BACKGROUND

This biomechanical study aimed to investigate root fracture thresholds and stress distributions in surrounding tissue while extracting three types of impacted mandibular third molars (horizontal, vertical, and mesioangular impactions) under varying dental elevator loading conditions.

METHODS

Mechanical tensile testing was conducted to determine the anisotropic properties and maximum fracture load of extracted teeth. Three-dimensional finite element models, reconstructed from cone beam computed tomography (CBCT) data, were used to simulate elevator-assisted extraction processes. Stress distributions and root fracture thresholds were analyzed under three loading modes (wedge, lever, and rotational force) at different abduction angles.

RESULTS

Horizontal impactions demonstrated the lowest fracture resistance under lever forces (38.7-50.3 N), while vertical impactions exhibited the highest thresholds (110.3-342.2 N). Wedge forces showed angular dependence inversely correlated with fracture thresholds for horizontal impactions (76-174 N). Rotational moments maintained relatively stable thresholds across all impaction types (X-axis: 21-32 N·m, Y-axis: 20-40.8 N·m, Z-axis: 16.3-33.5 N·m). Surrounding tissue stress decreased with increasing abduction angles under lever and wedge forces (p < 0.05) but no significant directional correlation was observed under rotational moments.

CONCLUSIONS

Dentin anisotropy and elevator angulation significantly influence fracture mechanics. Clinical protocols should prioritize lever forces for vertical impactions (safety margin > 100 N), with wedge and rotational force more effective for horizontal impaction. The findings provide an important theoretical basis for oral surgeons in extracting impacted third molars and for the subsequent development of surgical path planning and intelligent reasoning systems by the research group.