Effects of Prolonged Light Exposure Times on Water Sorption, Solubility and Cross-linking Density of Simplified Etch-and-Rinse Adhesives

Purpose: This study evaluated the effects of light exposure times on water sorption, solubility, and polymer cross-linking density of simplified etch-and-rinse adhesives. Materials and Methods: Four commercial adhesives (XP Bond, Adper Single Bond 2, Tetric N-Bond, and Ambar) were selected, and resin disks 5 mm in diameter and 1.0 mm thick were prepared and light cured for 20, 40, or 80 s using an LED light-curing unit at 1200 mW/cm2. Water sorption and solubility were evaluated over a 28-day period. For polymer cross-linking density, additional specimens were prepared and their Knoop hardness measured before and after immersion in 100% ethanol. The data from each test were evaluated using a two-way ANOVA and Tukey's test (α = 0.05). Results: The XP Bond adhesive showed higher water sorption (similar to Adper Single Bond 2) and solubility (p 0.05) than did the other materials. Prolonged exposure times did not reduce the water sorption but did reduce the solubility of all tested materials (p 0.05). For Ambar, the increase in the exposure time resulted in a significantly lower percent reduction in hardness. Conclusion: Water sorption, solubility, and cross-linking density of the materials selected in this study seem to be mainly influenced by the adhesive composition. Prolonged light exposure times reduced the solubility of the materials. Keywords: adhesives systems, water sorption, solubility, polymerization time