The aim of this study was to evaluate the biomechanical properties expressed by shrinkage stress, cuspal strain, fracture strength and failure mode in molars with large class II mesio-occlusal-distal restorations. Sixty-four human caries-free third molars were selected and distributed randomly into four groups: Z100 restorative material (Z100), Tetric N-Ceram Bulk-Fill (TNC), Filtek Bulk-Fill (FBF) and Aura Ultra Universal (ABF). The bulk-fill materials were inserted in one singular bulk increment and the conventional composite resin in three ones. Polymerisation shrinkage stress was evaluated by optical Fibre Bragg Gratings (FBG) sensors (n = 6). The cuspal deformation was measured using an extensometer during three moments: restorative procedure, axial compressive loading and at fracture (n = 10). The fracture strength was evaluated on a universal machine. The failure mode was analysed by Scanning Electron Microscopy (SEM). Data were analysed using one-way ANOVA tests with Tukey's posthoc test (α = 5%). Data of the failure mode were submitted to a likelihood ratio chi-square test. Z100 presented the highest mean value for the shrinkage stress (p 0.05). Bulk-fill composites promoted less polymerisation shrinkage stress than conventional microhybrid composite during and after the light curing process in class II posterior resin composite restorations98255261This study was supported by the Institute of Physics Gleb Wataghin (University of Campinas) and Dental Research Center Biomechanics, Biomaterials and Cell Biology (Dental School of Federal University of Uberlândia
