Purpose: To investigate the influence of different x-ray radiation doses on the bond strength of adhesive restorations to dentin using different bonding strategies. Materials and Methods: Flat dentin surfaces on human molars were obtained and cylinder-shaped specimens for the microshear bond test were built up with a composite (Z250, 3M ESPE), using three adhesive systems: a two-step etch-and-rinse (Single Bond 2 – SB2, 3M ESPE), a two-step self-etching (Clearfil SE Bond – CSE, Kuraray), or a singlestep self-etching (Adper Prompt – ADP, 3M ESPE). The specimens were assigned to 4 groups (n = 10), according to the x-ray dose: 0 (control), 5, 35, or 70 Gy. Radiation was directed to the surface of the resin cylinders. Microshear testing was conducted after 24 h, and the failure modes classified under magnification (200X). Data were submitted to two-way ANOVA and Holm-Sidak’s test (p ≤ 0.05). A nonlinear regression analysis was carried out with bond strength as dependent variable. Results: Bond strength results were dose and material dependent. SB2: control > 5 = 35 > 70; CSE: control = 5 > 35 = 70; ADP: control = 5 = 35 = 70. Generally, SB2 > CSE > ADP. The nonlinear regression plots showed that in general, an increase in radiation dose may predict a decrease in bond strength (R2 ≥ 0.905). Failure modes were dependent on the bonding system, generally with no significant influence of radiation. Conclusion: X-ray radiation might present a dose-dependent detrimental effect on the bond strength of resin composite restorations to dentin.

Keywords: adhesive systems, shear bond strength, dentin, radiation, radiotherapy, x-ray