RESUMO
This study examined the effect of different light activation modes for light-cured resin-based composites on the shear bond strength to dentin of two one-bottle adhesives with differing acidity. In this experimental study, a flat middle dentin surface was prepared on 110 extracted sound molars using a 600-grit polish paper. The teeth were then randomly divided into 10 equal groups (n = 11). One-Step Plus (OS) and Prime & Bond NT (P&B NT) were used according to the manufacturer's instruction with their respective composite (Aelite, Spectrum TPH) applied and cured using five different light-activation modes: 1. Conventional (CO): 600 mW/cm2 (40 seconds) 2. Soft-Start I (SSI): 100 mW/cm2 (10 seconds) 600 mW/cm2 (30 seconds) 3. Soft-Start II (SSII): 200 mW/cm2 (10 seconds), 600 mW/cm2 (30 seconds) 4. Pulse-Delay I (PDI): 100 mW/cm2 (3 seconds), 3-minute delay, 600 mW/cm2 (37 seconds) 5. Pulse-Delay II (PDII): 200 mW/cm2 (3 seconds), 3-minute delay, 600 mW/cm2 (37 seconds) After 24 hours storage in distilled water at room temperature, a shear bond strength (SBS) test was performed using an Instron machine at 1 mm/minute and the results were recorded in MPa. Statistical analysis included two-way ANOVA and Tukey HSD (p < 0.05). The highest SBS (MPa) was shown in the OS conventional group (19.62 +/- 2.21) and the lowest SBS was shown in P&B NT, PDII (5.93 +/- 1.79). In each group of five curing modes, the mean SBS for P&B NT was significantly lower than OS: conventional mode--P&B NT (17.27 +/- 1.98) vs OS (19.62 +/- 2.21); SSI-P&B NT (10.84 +/- 2.82) vs OS (13.09 +/- 1.24); SSII - P&B NT (14.78 +/- 1.63) vs OS (18.79 +/- 1.57); PDI-P&B NT (5.93 +/- 1.79) vs OS (11.97 +/- 2.59) and PDII-P&B NT (11.82 +/- 1.24) vs OS (16.00 +/- 1.62) (p < 0.001 for all comparisons). For each of the adhesives, the ranking of SBS was as follows: CO > SSII > PDII > SSI > PDI, with the two-paired comparisons of curing modes being significantly different (p < 0.05). The results of the current study indicated that the bond strength of P&B NT might be compromised by the higher acidity of this adhesive compared to OS during each curing mode, especially PDI. The conventional mode was least affected by the acidity of the adhesive.
