Effect of sonic-activated resin composites on the repair of aged substrates: an in vitro investigation

Abstract

This study aimed to evaluate whether sonic-activated resin-based composites (RBCs) used as repair materials might improve the repair bond strength of aged RBC substrates. Five RBCs were repaired by themselves and by all other materials. The repair was applied with and without sonic activation, resulting in 50 material application technique combinations (n = 15) and 750 specimens. The cohesive strength of the five materials was used as control (n = 15). Substrates were aged for 8 weeks in distilled water at 37 °C, roughened, cleaned with phosphoric acid, and repaired by using a silane primer and an adhesive as intermediate agents. The repair bond strength was assessed in a shear test. The modulus of elasticity (E) of the five RBCs was additionally evaluated in a three-point bending test. Results were compared using one- and multiple-way analyses of variance and Tukey's honestly significant difference post hoc test (α = 0.05), partial eta-square statistics, Pearson's correlation, and Weibull's analysis. No significant effect of sonic activation on the repair material was found in any material combination. The repair strength was 35.4-90.9 % of the cohesive strength of the original composites. E varied between 4.1 GPa (CLEARFIL MAJESTY Esthetic) and 9.7 GPa (CLEARFIL MAJESTY Posterior). The strongest influence on the shear bond strength was performed by E repair (η (2) P = 0.167), whereas the effect of E substrate was significant but low (η (2) P = 0.098). None of these parameters influenced the reliability of the repaired specimens (the Weibull parameter, m). The fracture pattern was mainly cohesive (93.3 %) in the control group and predominantly adhesive (89.2 %) in the repaired specimens. Except for the material with the highest modulus of elasticity used as a substrate material, it was not detrimental to combine different RBCs in terms of repair. If a substrate material is unknown, the recommendation for repairing would be in favor of a material with a high modulus of elasticity.