Effect of additional coating of bonding resin on the microtensile bond strength of self-etching adhesives to dentin
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Abstract
Abstract
This study investigated the hypothesis that the dentin bond strength of self-etching adhesive (SEA) might be improved by applying additional layer of bonding resin that might alleviate the pH difference between the SEA and the restorative composite resin. Two SEAs were used in this study; Experimental SEA (Exp, pH: 1.96) and Adper Prompt (AP, 3M ESPE, USA, pH: 1.0). In the control groups, they were applied with two sequential coats. In the experimental groups, after applying the first coat of assigned SEAs, the D/E bonding resin of All-Bond 2 (Bisco Inc., USA, pH: 6.9) was applied as the intermediate adhesive. Z-250 (3M ESPE, USA) composite resin was built-up in order to prepare hourglass-shaped specimens. The microtensile bond strength (MTBS) was measured and the effect of the intermediate layer on the bond strength was analyzed for each SEA using t-test. The fracture mode of each specimen was inspected using stereomicroscope and Field Emission Scanning Electron Microscope (FE-SEM). When D/E bonding resin was applied as the second coat, MTBS was significantly higher than that of the control groups. The incidence of the failure between the adhesive and the composite or between the adhesive and dentin decreased and that of the failure within the adhesive layer increased. According to the results, applying the bonding resin of neutral pH can increase the bond strength of SEAs by alleviating the difference in acidity between the SEA and restorative composite resin.

Microtensile bond strength (MTBS) to dentin. When D/E bonding resin was used as the second coat over the first coat of SEA, the MTBS of each SEA increased significantly.

FE-SEM micrograph of two coats of the Experimental SEA. (A) fractured surface of resin side. (B) fractured surface of dentin side. Dentinal tubules were seen (arrow). Failures at the bottom or at the top of the hybrid layer locating between the adhesive layer and the dentin was observed.

FE-SEM micrograph of the Experimental SEA and D/E bonding resin. (A) fractured surface of resin side. (B) corresponding surface of dentin side. Fracture within the adhesive layer was observed as smooth surface. The fracture plane deviated into the composite resin (arrow).

FE-SEM micrograph of two coats of Adper Prompt. (A) fractured surface of resin side. (B) fractured surface of dentin side. Honeycomb appearance with much irregular voids was seen in dentin side (B).

FE-SEM micrograph of Adper Prompt and D/E bonding resin. (A) fractured surface of resin side. (B) corresponding surface of dentin side. The failure was classified as a mixed one.