Delayed Curing and Dentin Shear Bond Strength

Quadrant dentistry is commonly done using composite resin restorations.  At times the bonding agent may be applied to several preparations, cured and some time may elapse before the composite resin is placed and cured over the cured adhesive.  Objectives: To measure and compare the shear bond strength when the adhesive is light cured immediately after placement and after a 1, 10 and 20 minute delay between curing the adhesive and placing and curing the composite.  Methods: 80 extracted teeth were ground to produce a flat dentin surface using abrasive discs ending with 320 grit.  Single Bond or One Coat was applied to the bonding area of 10 teeth following the manufacturers' directions. A tube filled with composite resin was placed and immediately cured over the adhesive.  To 3 other groups a delay between curing the adhesive and curing the composite was added: (n=10) a 1 minute, 10 minute or a 20 minute delay. The specimens were stored at room temperature in phosphate buffered saline until testing.  The specimens were placed in a fixture in an Instron model 1144 and loaded in shear at a 1 mm/min crosshead speed until failure.  The shear bond strength for each group was calculated for each group.  General linear model ANOVA was used to analyze the shear bond strength (MPa) of Single Bond and One Coat at 4 time points. Mean comparisons were made by using Tukey's HSD.  Results: No significant difference were found among four time points with either bonding agent (Single Bond, p=0.08 or One coat, p=0.10). Significant differences in bond strength were provided by the different bonding agents.  Time had no difference on bond strength.    Conclusion: Delayed placement and curing of the composite resin within 20 minutes does not affect the dentin bond strength of composite.