Influence of radiation on bond strength

Purpose: The aim of this in vitro study was to evaluate the shear bond strength of two adhesive systems-Prime & Bond NT (PBNT) and Clearfil SE Bond (CSEB)-to dentin irradiated before or after adhesive application. Materials and Methods: Thirty extracted molars were sectioned mesiodistally with a diamond bur. The inner surface of each tooth's dentin was ground flat with SiC abrasive papers. The roots of the sectioned teeth were mounted in a cylindrical mold using chemically cured acrylic resin. In groups A1 and B1, a radiation dose of 60 Gy (R) was applied to the dentin surfaces at this point. In all groups, adhesives were applied according to the respective manufacturer's instructions. Cylindrical composite resin restorations (CRR; internal diameter 3 mm, height 4 mm) were then placed on the center of the flattened dentin surfaces. At this point, groups A2 and B2 received 60 Gy of radiation, and groups C1 and C2 remained as nonirradiated controls. Thus, the test groups were: A1: R+PBNT (Primed Bond NT)+CRR; A2: PBNT+CRR+R; B1:R+CSEB (Clearfil SE Bond)+CRR; B2:CSEB+CRR+R; C1:PBNT+CRR; C2:CSEB+CRR. Specimens were mounted in a universal testing machine and shear load was applied at a crosshead speed of 1 mm/min until failure. Bond strength values were calculated as MPa and the results were evaluated statistically using repeated measures of two-way ANOVA, with significance set at p<0.05. Results: Irradiation significantly affected adhesion of composite to dentin in groups A1 and A2 (p=0.002). Group A1 showed statistically lower bond strength than group A2 (p<0.05). No statistically significant differences were found among the other groups (p=0.49). Conclusion: The time point of irradiation can have an adverse effect on bond strength, depending on the type of adhesive material.