Root-level vulnerability and lingual plate fracture risk in mandibular third molars: A retrospective CBCT-based cross-sectional study

Background: Prior studies investigating the relationship between lingual plate (LP) fracture risk and mandibular third molar (M3M) anatomy have produced inconsistent findings. Factors such as age, sex, impaction depth, and buccolingual angulation have shown variable associations with fracture risk. Importantly, M3M rotational angulation has rarely been evaluated. While most research has focused on the middle and apical thirds of the root, one clinical study suggested the cemento-enamel junction may represent a structurally vulnerable site. Objectives: This study aimed to identify anatomical and demographic risk factors associated with LP fracture across the coronal, middle, and apical thirds of the M3M root. Methods: Cone beam computed tomography (CBCT) images of 300 mandibular third molars were retrospectively reviewed. Data collected included patient sex, age, tooth side, and spatial alignment. M3M root length was measured and divided into coronal, middle, and apical thirds. The thinnest LP region at each level was recorded, and fracture risk was classified into three categories: low, moderate, and high. Ordinal logistic regression was used to determine significant risk factors. Results: Fracture risk was significantly lower in the coronal third compared to the middle and apical thirds. Younger patients exhibited higher fracture risk at all levels. Greater root length increased risk at the apical third. Horizontal impaction level II, mesial and horizontal angulations, and buccal inclination were associated with elevated risk, while lingual inclination and rotational angulation reduced risk. Conclusion: Age, root morphology, impaction depth, and three-dimensional M3M angulations are key predictors of LP fracture risk at distinct root levels.