Time Sensitivity Associated with Application of HEMA-free Adhesive

Abstract

Background: Acetone is one of the solvents incorporated in HEMA-free dental adhesives. Since acetone is very sensitive with high vapor pressure, acetone-based adhesives necessitate great care and attention in handling and application. Objective: The aim of this study was to determine the optimal application time of acetone-based HEMA-free adhesive by conducting micro tensile bond strength test (MTBS) at different time intervals. Materials and Methods: Twelve freshly extracted non-carious human molars were collected. Two-thirds of the roots were removed and the coronal part of the teeth was subjected to horizontal cross-sectioning in order to remove their cusps and expose the superficial coronal dentin. Then, the teeth were randomly divided into 4 groups (3 teeth each) according to the adhesive application time before curing. One- step self-etch HEMA-free adhesive (G bond; GC, Japan) and universal resin composite (Kalore; GC, Japan) were used in this study. In group (A), application of adhesive was carried out for 15 sec as recommended by the manufacturer instructions. In groups (B), (C) and (D), the adhesive was applied for 30 sec, 1 min and 5 min, respectively, before curing. After 24-hour storage in distilled water at 37°C, each tooth was cross-sectioned into micro beams and subjected to MTBS test by using a universal testing machine. Results: The tests showed statistically significant differences among the groups (P = 0.00) with each group is different from the others (P = 0.00). Group A had the highest mean strength value followed by groups B, C and then D with 57.7, 41.6, 29.7 and 17.1 MPa, respectively. Conclusion: The tested adhesive might be sensitive to application time as shown by superior MTBS results when its application time lasts for 15 seconds. This might be explained by evaporation of acetone in one-step acetone-based self-etch adhesives.