Effect of the number of applications of acetone-based adhesives on microtensile bond strength and the hybrid layer

Purpose: The current study was carried out to evaluate the effect of doubling the adhesive layers of three acetone-based adhesives on the microtensile bond strength and ultra morphological characterization of the resin dentin interface using SEM. Materials and Methods: A total of 27 caries-free human molars were used. Superficial flat dentin surfaces were obtained by wet grinding the buccal surfaces. Three adhesive systems Prime & Bond NT (G1), XENO IV (GII) and G BOND (GIII) were used according to three different protocols: (A) according to the manufacturer's instructions, (B) doubling the adhesive layers and light curing and (C): doubling the adhesive layers with intermediate curing between each layer. Resin composite buildups were made using TPH Spectrum resin composite on the bonded surfaces in 1 nun light cured increments for 40 seconds each. The bonded teeth were sectioned to obtain sticks for microtensile testing. The testing was conducted using a universal testing machine at a crosshead speed of 1 mm/minute. The microtensile bond strength means and standard deviations were calculated and the data were statistically analyzed using Two-way Analysis of Variance (ANOVA) and Tukey's post-hoc tests (p≤0.05). Ultra morphological characterization of the resin-dentin interface and representative fractured dentin specimens were examined using SEM. Results: When applied according to the manufacturer's instructions, Prime & Bond NT (total etch adhesive) showed significantly high microtensile bond strength with a mean value ± SD of 35 ± 12.7 MPa foUowed by XENO IV (21.2 ± 9.4 MPa), while G BOND presented a significantly lower mean value (10.9 ± 2.9MPa). Doubling the adhesive layers significantly reduced the mean strength of the total etch adhesive system; in contrast, it significantly increased the bond strength of both self-etch adhesives. The relatively thicker adhesive layer was seen with the total-etch adhesive when the application was doubled, while the hybrid layer appeared thicker with self-etch adhesives. Conclusions: Doubling the adhesive layer applications significantly improved the bond strength of the two self-etch adhesives (XENO IV and G BOND); however, it had a negative effect on the bond strength of the total-etch adhesive (Prime & Bond NT).