In vitro effects of different preparation techniques on shear bond strength of direct composite resin to indirect composite resin

Introduction: Sometimes repair of indirect composite restorations is preferable to replacement. The aim of this study was to investigate the effect of different surface preparations of indirect composite resin restoration on the shear bond strength of direct composite resin to it.Materials and Methods: In this in vitro study eighty blocks of indirect composite resin were manufactured and randomly assigned to different surface treatment groups (n = 20): control group (CG), no surface preparation; group 2, sandblasting with alumina particles (SBG); group 3, acid etching with 9.5% hydrofluoric acid (HA); and group 4, acid etching with 37% phosphoric acid (PAG). The blocks were restored with direct composite resin and stored in an incubator for 24 hours after thermocycling (500 cycles at 5/55 ± 2°C). The specimens (n = 80) underwent fracture tests in an Instron instrument. Data were analyzed using one-way ANOVA and Tukey test (α = 0.05).Results: The highest shear bond strength values with a mean of 25.93 MPa were recorded in group 3 (p value < 0.001). The lowest shear bond strength values were recorded in groups 1 and 2 with 11.00 ± 1.83 and 12.54 ± 2.47 MPa, respectively (p value = 0.097). There were significant differences between all the groups except for groups 1 and 2 (p value ≤ 0.001).Conclusion: Based on the results, surface treatment technique influences the shear bond strength of indirect composite resin to direct composite resin and the best technique is etching with hydrofluoric acid. Key words: Composite resins, Hydrofluoric acid, Sandblasting, Shear bond strength