Effect of 2-(Methacryloxy)ethyl Phenyl Hydrogen Phosphate on Adhesion to Dentin

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Abstract
A variety of methacrylate-based materials has been developed with the capacity of adhering to dentin. This study investigated the effectiveness of 2-(methacryloxy)ethyl phenyl hydrogenphosphate (phenyl-P) for bonding 5% phenyl-P in methyl methacrylate (MMA) to dentinal surfaces. Polymerization of the phenyl-P/MMA monomer was initiated by partially oxidized tri-n-butyl borane catalyst (TBB). The mean tensile bond strength of 5% phenyl-P in MMA to dentin that was pre-treated with an aqueous solution of 10% citric acid/3% ferric chloride, abbreviated as 10-3, was found to be 10.5 MPa. Scanning electron microscope examination demonstrated the formation of a transitional or "hybrid" layer of resin-reinforced dentin, created by the intermingling and entanglement of polymerized resin with collagen bundles exposed by dentin pre-treatment with 10-3, an effective remover of the dentinal smear layer. This "hybrid" layer or zone was essential for high tensile bond strength to be attained. Phenyl-P was found to be effective in promoting monomer diffusion and impregnating monomer into demineralized dentinal surfaces. The formation of the "hybrid" layer of resin-reinforced dentin followed in situ resin polymerization initiated by partially oxidized tri-n-butyl borane (TBB). Ferric (Fe3+) ions deposited on dentinal surfaces from the 10-3 solution also acted to improve monomer diffusion and entanglement with demineralized dentin, and facilitated the formation of the "hybrid" layer/zone.