Influence of occlusal loading type and cyclic fatigue on the mechanical behavior of sound maxillary premolars: a laboratory and 3D finite element analysis

This study evaluated the influence of different occlusal loading and cyclic fatigue on the biomechanical behavior of sound maxillary premolars using three-dimensional (3D) finite element analysis (FE) and strain-gauge tests. The 3D models were submitted to two occlusal loading (150 N): axial load (AL) and oblique load (OL), applied at the inner ridges. Dynamic fatigue was simulated in post-processing and analyzed by life criterion. For the experimental laboratory test, 30 sound premolars with similar dimensions had two strain gauges positioned parallel to the long axis of enamel and dentin to record the strains under AL and OL loading, before and after mechanical fatigue. FE maximum principal criteria showed higher stress concentration in the cervical enamel and dentin for OL (67.26 MPa and 17.43 MPa, respectively) compared to AL (0.87 MPa and 0.02 MPa, respectively). The equivalent elastic strain criterion showed higher strain values in dentin for OL (1.77e-4). The FE fatigue simulation showed higher damage for enamel near the cementoenamel junction with OL, predicting a lifespan of less than 200,000 cycles. Strain-gauge analysis showed that OL loading and mechanical fatigue resulted in higher strains, both enamel (p<0.001) and dentin (p<0.001). Very strong (0.927) and weak (0.184) correlations were found between the number of cycles and strain magnitude for enamel (p<0.0001) and dentin (p=0.0374), respectively. Non-axial occlusal loading, combined with cyclic mechanical fatigue, promotes high stress and strain concentration in the cervical enamel and dentin of sound premolars, potentially causing more damage to dental structures.