Influence of the shape, materials and occlusal mode of the maxillary first premolars on stress in noncarious cervical lesions

To study the stress distribution in non-carious cervical lesions (NCCLs) of maxillary first premolars under the conditions of different defect shapes, restorative materials and loading directions and to analyze the effect of different conditions on the treatment of NCCLs.

Three-dimensional finite element models of cervical defects of the maxillary first premolar were established by oral CBCT in a healthy adult. According to the shape of the cavity bottom, the cavity was divided into two groups: acute angle and obtuse angle. In addition to healthy dental controls, defects in each group were simulated and virtually treated with three kinds of restorative materials (glass ionomer cement, Z350 resin and bulk resin) as research objects. Four kinds of loads (normal occlusal vertical load, normal occlusal lateral load, traumatic occlusal vertical and lateral load) were applied. The lateral load of occlusion was 100 N, and the stress distribution in the prosthesis was analyzed.

Under the condition with different cavity types that the NCCL near the pulp line was sharp, the stress in the wedge-shaped defect repair material was concentrated and significantly higher than that in the other obtuse groups. Under the condition with different repair materials, in the bottom of the acute cavity, the glass ionomer cement showed less stress than the two kinds of resin. The maximum stress in the prosthetic material in the traumatic occlusion state was significantly higher than that in the normal occlusion state, and the lateral load was more concentrated than the vertical load on the neck defect.

The stress in maxillary first premolar NCCLs is affected by the shape of the cavity and the loading direction. A simulated acute cavity morphology and traumatic force mode produced concentrated stress in the material used to repair the NCCL. Before restoration, the bottom of an acute cavity should be adjusted to an obtuse angle. After treatment, the bite of the affected tooth adjusts over time to reduce traumatic occlusion, which is beneficial for improving the service life of the filling material.