The Study On Chemical Bonding Mechanism Between The Phosphoric Acid Esters And Enamel

Background: Self-etching adhesives is a new-style system. It has been widely used in contemporary dentistry. The functional monomers of self-etching adhesives are carboxylic acids, derivatives of carboxylic acid, or phosphoric acid esters. Previous studies revealed that self-etching adhesives could decalcify and chemically adhere to hydroxyapatite(HA). However, the chemical bonding mechanism of phosphoric acid esters' (PAEs) interactions with enamel substance has not been fully clarified.Objective: This study was to investigate the evidence of the chemical bonding of the self-etching primers containing phosphoric acid esters (PAEs) to enamel.Materials and Methods:FTIR: After three self-etching adhesive systems' primers- Pompt L-Pop, SE BOND, Xeno III were respectively mixed with thirty mg enamel powder under room temperature for 48 h, the reaction products were rinsed with 10 ml deionized water for three times ,then the filtered solid materials were dried over a vacuum silica gel. Then , three primers painted on the KBr discs were subjected to the spectroscopic determinations with Fourier transform infrared spectroscopy (FTIR). The enamel powder and the corresponding solid materials were respectively milled and alsoanalyzed by FTIR.NMR: Ten mg enamel powder was submerged with one of three self-etching adhesive systems' primers- Pompt L-Pop, SE BOND, Xeno III at room temperature for 48 h .Then the reaction products and three primers in deuterium water(D2O) were respectively analyzed by ³¹P NMR. After these reaction products were rinsed with 10 ml deionized water for three times , the filtered solid materials were dried over a vacuum silica gel prior to ³¹P NMR in CDCl₃.Results:FTIR: When self-etching primers containing phosphoric acid esters reacted with enamel powder, there still existed the typical bands of primers such as some carbonyl groups (C=O), double bands (C=C) etc., and of enamel such as the phosphoric groups (P-O, P=O). The reaction product's spectra were subtracted by the enamel's, the subtracted spectra revealed some changes of the phosphoric groups from 1200 cm^-1 to 800 cm^-1.NMR:. The phosphorus-31 peaks of the Prompt L-pop in D2O (deuterium oxide) revealed three main peaks at the range of 1.244 - 1.361 ppm. After the primer was mixed with enamel powder in D2O, the ³¹P NMR peaks shifted to the range of 0.873 -1.115 ppm. The spectrum of the solid separating from the reaction detected in CDCl3(deuterium chloroform) showed four main peaks from-1.537 ppm to 0.168 ppm.The phosphorus-31 peaks of the Xeno III in D2O revealed eight main peaks at the range of -7.165-1.158ppm. After the primer was mixed with enamel powder in D2O, the ³¹P NMR peaks were at the range of -10.767-0.551 ppm, the spectrum of the solid separating from the reaction detected in CDCl₃ showed three main peaks from 0.947 ppm to 1.119 ppm.The phosphorus-31 peaks of the SE Bond in D2O revealed three main peaks atthe range of 0.488 - 0.775 ppm. After the primer was mixed with enamel powder in D2O, the ³¹P NMR peaks were at the range of 0.848 -1.326 ppm, the spectrum of the solid separating from the reaction detected in CDCl₃ showed two main peaks from -10.033 ppm to 1.224 ppm.Conclusion: Self-etching primers containing phosphoric acid esters (PAEs) can decalcify enamel and chemisorbed with enamel simultaneously.