Low torque is a risk factor for non-carious cervical lesions (NCCLs) in maxillary premolars

To determine the prevalence of non-carious cervical lesions (NCCLs) in maxillary premolars of different torques and simulated cervical stress profiles of the premolars under coincident loadings using finite element analysis (FEA).

The CBCT scans of 616 maxillary premolars from 154 subjects were retrospectively evaluated. The premolars were ascribed into low torque group (LTG) <-10.9°, medium torque group (MTG) -10.9° to -3.9°, and high torque group (HTG) >-3.9°, when the torque was referring to the occlusion plane. The prevalence of NCCLs in each group was evaluated. Then finite element models of a maxillary first premolar, its adjacent teeth and alveolar bone were established. The models were prepared with ANSYS software generating the premolars presenting different torques. The mastication scenario for the premolars in maximum intercuspation position was simulated.

The prevalence of NCCLs was 15.7% in LTG, 7.9% in MTG and 5.5% in HTG. The prevalence of LTG was significantly higher than that of MTG (P< 0.05) and HTG (P< 0.01). As for FEA, the stresses at the buccal necks of the premolars basically increased with decrease of the torque. The tensile stress peaks were in the cemento-enamel junction in most premolars of the LTG, while in the middle of the crowns in premolars of MTG and HTG.

Low torque with excessive lingual inclination is a risk factor for NCCLs of maxillary premolars, and excessive tensile stress concentration in buccal necks during mastication may be responsible for that.