Effect of the composite photoactivation mode on microtensile bond strength and Knoop microhardness

Objective This study evaluated the effect of the composite photoactivation mode on microtensile bond strength and Knoop microhardness. Methods Standard class I cavities (3×4×3 mm) were restored with two adhesives systems, Single Bond (SB) and Clearfil SE Bond (CE), and the TPH composite. The photoactivation of the composite was carried out using three modes: Conventional (CO: 400 mW/cm2×40 s), Soft-Start (SS: 100 mW/cm2×10 s+600 mW/cm2×30 s) and Pulse-Delay (PD: 100 mW/cm2×3 s+3 min wait+600 mW/cm2×37 s). For the microtensile test, beams obtained from the buccal wall bond interface were tested under tension at 0.5 mm/min crosshead speed until failure. For the microhardness test, the restorations were sectioned in the mesio-distal direction and indentations were made on the internal composite surface of each half at three different depths. Data of two tests were analyzed using two-way ANOVA and LSMeans (α=0.05). Results In the microtensile test, SS presented the highest values. PD presented intermediate values without differing significantly from the other modes. For adhesives, SB presented the highest values. In the microhardness test, PD presented the highest values, differing significantly from SS. CO presented intermediate values but without any statistical difference from the others. The SS–CE interaction presented the lowest values with statistical differences from all the others. Significance By the SS technique, the highest bond strength was obtained. However, this technique made it possible for the adhesive system to intervene with the hardness of the composite.