Effect of Doubling Applications of Acetone-Adhesives on Microtensile Bond Strength

Purpose: This study evaluated the effect of doubling the number of applications of acetone-based adhesives on bond strength and on ultra-morphological characterization of the hybrid layer. Methods: Flat dentinal surfaces were exposed from 27 sound extracted human molars by wet grinding. Three adhesives: Prime & Bond-NT (G1), Xeno-IV (G2) and G-Bond (G3) were used to bond TPH Spectrum resin composite build ups (Dentsply). Adhesives were applied following three different protocols: (A) according to manufacturers' instructions, (B) by doubling the number of the adhesive layers followed by light curing and (C) by doubling the number of the adhesive layers and curing each layer. Bonded teeth were each sectioned to 16 resin/dentin beams with cross sectional area of 0.8X 0.8 mm. Six sticks were selected from each tooth and used for micro-tensile testing using universal testing machine at a crosshead speed of 1mm/min (n=18). Microtensile bond strengths means and SDs were calculated and data statistically-analyzed using two-way ANOVA and Tukey's post-hoc tests. Representative fractured specimens were examined using SEM to assess the ultra-morphological characterization of the resin-dentin interface. Results: Under protocol (A), G1 showed significantly higher (P<.05) microtensile bond strength (35±12.7 MPa) followed by G2 (21.2±9.4 MPa) while G3 showed the lowest microtensile strength value (10.9±2.9 MPa). Protocol (B) significantly lowered the bond strength of G1 (Prime and Bond NT), while it significantly increased the bond strength values for both self-etch adhesive systems. SEM results presented thicker hybrid layer with total-etch adhesive compared to self-etching adhesives. Doubling the number of layers increased the thickness of the hybrid layer of all adhesives examined. Conclusions: Doubling the number of adhesive layer applications significantly improved the bond strength of the two self etch adhesives examined, however, it had a negative effect on the total etch adhesive.

Acknowledgments:Dentsply