Influence of hydrophobic resin coating on micro-tensile bond strength of different adhesives: an in – vitro study

Recently, the etch-and-rinse and self-etching approaches are the two strategies of resin-based adhesive systems to accomplish the bonding to enamel and dentin. The increased amount of solvents and hydrophilic monomers in the adhesive formulations lead to greater amount of residual solvents entrapped in the adhesive layer. Consequently, the resulting polymers will be more susceptible to degradation over time. One of the methods for more durable bond includes the application of an additional layer of a hydrophobic resin coating over the polymerized simplified adhesive. The aim of this in –vitro study was to evaluate the influence of hydrophobic resin coating on micro-tensile bond strength of different adhesives Eighty freshly sound human molars were divided into three main groups according to method of bonding (A), where (A1) represents teeth bonded using Single Bond Universal Adhesive in total each approach, (A2) represents teeth bonded using Single Bond Universal Adhesive in self-etch approach while (A3) represents teeth bonded using Self Etch Future Single Bond DC Bonding System. Each (A) group will be then subdivided into two additional subgroups according to the addition of hydrophobic resin coating into (B1) which stands for teeth with additional hydrophobic resin coating and (B2) which stands for teeth without additional of hydrophobic resin coating. Each (AB) group will be finally subdivided into two smaller subgroups according to the effect of thermocycling, where (T1) denotes the teeth which were thermocycled, and (T2) denotes the teeth which were not thermocycled. The occlusal dentin surface of each molar was prepared on two levels: Superficial level (below the dentino enamel junction by 0.5 mm) and deep level (below the dentino enamel junction by 1.5 mm). For all specimens, after bonding procedures either total etch or self etch, a hydrophobic resin coating was added for the assigned groups. Resin composite was applied; thermo-cycling was done for the assigned groups. Teeth were sectioned into a series of 1 mm thick slabs and microtensile bond strength testing was done. Two representative specimens of each group were selected for Ultramorphological Examination. Mode of application, addition of adhesive layer and thermocycling had a significant effect on bond strength. Within the limits of this study, we concluded that regarding bonding efficacy to enamel and dentine, conventional 3-step etch-and-rinse adhesives are still not surpassed by the newer simplified self etch adhesive systems. Addition of the hydrophobic bonding resin coating improved bonding to dentine especially when used with all-in-one self-etch adhesive systems.