Effect of Curing-time on Oxygen-inhibited Layer Thickness and Bond Strength

Objectives: This study investigated the hypothesis that increasing light-curing time would leave the oxygen-inhibited layer (OIL) of adhesive thinner, and in turn, result in lower shear bond strength (SBS) than those by routine curing procedures. Methods: 120 human posterior teeth were randomly divided into three groups for bonding with adhesives: All Bond 2, One Step, and Adper Prompt. They were subsequently divided into four subgroups with different light-curing times (10, 20, 30 and 60 s). The assigned adhesives were applied on superficial occlusal dentin according to the manufacturer's instructions and cured for one of the four curing times. Composite resin cylinder, 2.35 mm in diameter, were built on the adhesive and light-cured for 40 s. SBS were measured after 24 h from the bonding using a universal testing machine (crosshead speed 1.0 mm/min). The relative thickness of the OIL and the degree of conversion (DC) were determined from the adhesives on a slide glass using FT-NIR in an absorbance mode. Data were analysed with One-way ANOVA and Duncan's multiple test (p < 0.05). Results: With increasing cure time, although there were no significant difference in the SBS of One-step and Adper Prompt (p > 0.05), those of All Bond 2 decreased significantly(p < 0.05). The relative thicknesses of the OIL on each adhesive were not affected by the cure time (p > 0.05). Although the DC of All-Bond 2 were statistically not different with increasing cure time (p > 0.05), those of One-Step and Adper Prompt showed an increasing trends with increasing cure time (p < 0.05). Conclusions: Increasing light-curing time did not affect on the relative thickness of the OIL of the adhesives, and in turn, on the SBS to dentin. This study was supported by SNU foundation.