Effect of delayed light-cured activation on bond-strengths between composites and adhesives

The objective of this study was to evaluate and compare the effect of times elapsed on the application of a single-step adhesive system and activation of light cured subsequently placed composite to the bond strength between composites and adhesives. This was an experimental study using fifteen teeth extracted human premolars, which were caries and pathology free. Sample of teeth were embedded up to cemento-enamel junction on box of acrylic resin. All teeth were cut to obtain flat occlusal dentin surfaces. The specimens were randomly selected and divided into three groups with five teeth each. All the teeth were assigned to single-step bonding system AQ Bond (Sun Medical Co. Ltd., Shiga, Japan) according to manufacturer’s direction. Group 1 was left for 45 seconds, group 2 for 2 minutes, while group 3 was 5 minutes before putting subsequently restorative material. Composite resin was applied in 3 mm diameter and 6 mm height of cylinder mold and cured according to manufacturer’s direction on the dentin surface. Shear bond strength were measured using a testing system (Instron 8874, Instron Corp., Canton, MA, USA) at a crosshead speed of 2 mm/min with cell load capacity of 25 KN. The bond-strengths between single step adhesive system (AQ Bond) and light cured composites were tested. Mann-Whitney test showed no significant differences in bond-strength between Group 1 and Group 2. However, there were significantly differences (p<0.01) in decreased of bond-strength between Group 2 and Group 3. As conclusion, the bond strength between composites and single-step adhesive system was reduced after 5 minutes delayed curing of composites.