Effect of aging on microshearing bond strength of different adhesive systems

Reliable bonding agents are essential for durable tooth-colored restorations. This study aimed to evaluate the effects of a two-step self-etch adhesive and a universal adhesive (used in self-etch and etch-and-rinse modes) on dentin microshear bond strength and the impact of 1-year simulated thermal aging. In this study, 60 caries-free human incisors were used. A two-step self-etch adhesive system (SE) (Clearfil SE Bond; Kuraray Noritake Dental, Japan), a universal adhesive in self-etch mode (U-SE) (Clearfil S3 Bond Universal; Kuraray Noritake Dental, Japan), and the same universal adhesive in etch-and-rinse mode (U-ER) were tested. The specimens were randomly divided into six groups (n = 10 per group): (1) SE, initial measurement without aging (T0); (2) U-SE, initial measurement without aging (T0); (3) U-ER, initial measurement without aging (T0); (4) SE, after artificial aging (T1); (5) U-SE, after artificial aging (T1); and (6) U-ER, after artificial aging (T1). Artificial aging was performed by 10,000 thermal cycles between 5 °C and 55 °C, simulating approximately one year of intraoral conditions. The prepared samples were evaluated using the microshear bond strength test. Non-parametric tests were applied for statistical analysis due to the small sample size and non-normal data distribution, with significance set at p < 0.05. The SE without aging group 1 (15.70 MPa) and SE aged group 4 (11.82 MPa) showed the highest bond strength values, while the U-ER without aging group 3 and aged group 6 consistently presented the lowest (6.58 MPa, 6.33 MPa). After 1-year artificial aging, bond strength significantly decreased in the SE (p<0.05) and U-SE (p<0.05) groups, whereas no significant change was observed in the U-ER group (p>0.05). Overall, statistical analysis confirmed significant differences among the adhesive systems and aging conditions (p<0.05). According to the results of this study, when the micro shear bond strengths of dentin adhesive systems were compared, it was found that the SE group showed higher bond strength values than the U-ER and U-SE groups at the beginning and after 1-year aging simulation.