RESUMO
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 (nâ¯=â¯6). The cuspal deformation was measured using an extensometer during three moments: restorative procedure, axial compressive loading and at fracture (nâ¯=â¯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 (αâ¯=â¯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 (pâ¯<â¯0.05) by FBG evaluation, whereas bulk-fill resin groups presented low polymerisation stress mean value, especially the TNC (pâ¯<â¯0.05). The cuspal deformation test showed that Z100 presented a significant difference mean value compared to the other groups (pâ¯<â¯0.01) during the restoration and compressive axial force; however, load until the fracture presented a difference only between TNC and FBF (pâ¯<â¯0.05). The fracture strength of TNC was statistically different from Z100 (pâ¯<â¯0.01). The failure mode was not statistically different in all the groups (pâ¯>â¯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 restorations.