Effect of selective carious tissue removal on biomechanical behavior of class II bulk-fill dental composite restorations

•Caries-affected dentin was induced in the pulpal floor of class II cavities.•Restorations were built-up after selective or non-selective caries removal.•Caries removal protocol did not affect the cusp deformation and crack propagation.•Maintaining caries-affected dentin did not affect the fracture strength of restoration. This study aimed to develop a method to induce carious lesions in the pulpal floor dentin of a class II cavity preparation, and to determine the effects of this carious lesion on the biomechanical behavior of the dental composite restoration. The pulpal floor dentin of class I cavities in sound third molars were demineralised with acetic acid for 35days followed by a 7-day exposure to pooled human saliva biofilm and demineralization was verified by micro-CT. Subsequently, the proximal walls were removed forming a class II cavity and the caries lesion was left intact or was completely removed prior to restoration with a bulk-fill dental composite (n=10). Cuspal deflection was assessed by strain-gauge and micro-CT imaging. The presence of enamel cracks was assessed by transillumination before and after restoration, and again after 1,200,000 cycles of mechanical fatigue in a chewing simulator. Finally, resistance to fracture by axial compressive loading and failure mode was determined. Data were analyzed by 2-way repeated measures ANOVA, Fisher’s exact test, and t-test (α=0.05). The presence of carious lesions had no significant effect upon cuspal deflection, formation of enamel cracks, and fracture strength of the dental composite restorations. The restorative procedure increased the number of enamel cracks, which was not affected by mechanical cycling. Maintaining carious lesions does not affect the biomechanical behavior of class II restorations performed with bulk-fill dental composite.