Objectives: 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.
Materials and methods: 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: 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.
Conclusions: 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.
Clinical relevance: If a substrate material is unknown, the recommendation for repairing would be in favor of a material with a high modulus of elasticity.