The Study On Chemical Bonding Of The Self-etching Primers To Hydroxyapatite

Background: Self-etching adhesives is promising in the contemporary adhesive dentistry. The self-etching primers can partly decalcify the tooth hard substrates, permeate into the intact enamel and dentin, and are polymerized in situ. The self-etching primers are used as a smear layer dissolving reagent and a dentin primer, so the self-etching adhesives eliminate the acid-etching and water-rinsing steps and simplify the clinical application procedures. Previous studies on self-etching adhesives were focused on bond strength of resin-to-enamel/dentin, margin adaptation at the resin-enamel/dentin and the stimulation of self-etching adhesives to dental pulpal tissue. However the chemical bonding mechanism of the self-etching primers to hydroxyapatite (HA) has not been fully elucidated.Objective: This study was to investigate the evidence of the chemical bonding of the self-etching primers to hydroxyapatite. Materials and Methods:FTIR: After seven self-etching adhesive systems' primers (Syntac, Solobond Plus, Ecusit- Primer-Mono, Solid Bond P and Resulcin AquaPrimer, CleafiL Liner Bond 2V, and Pompt L-Pop) and a non-reactive bonding agent containing Bis-GMA were respectively mixed with HA particles under room temperature for 48 h, they were dried over a vacuum silica gel. The corresponding mixtures and the HA were respectively milled and analyzed by Fourier transform infrared spectroscopy (FTIR) before the subtraction technique were performed. Eight primers painted on the KBr discs weresubjected to the spectroscopic determinations by FTIR.ATR: HA disks were sintered under 1100 for 2 hours. The HA disks were preparedat 4 mm long, 4 mm wide and 2 mm thick. The self-etching primers were respectivelysmeared on HA disks, left them undisturbed for 60 s, rinsed and dried before all thesamples were analyzed by attenuated total reflectance (ATR). The subtraction techniquewere performed .NMR: A self-etching primer containing phosphoric acid ester, M2P, (ResulcinAquaPrime A) reacted with HA particles or Ca(OD)2 resulting from the reaction of CaOwith deuterated water (D2O). The reaction products and M2P were analyzed byphosphorus-31 Nuclear Magnetic Resonance (31P NMR) in deuterium oxide. M2P, thesolid reaction products, and the supernant solution of the reaction products wereanalyzed by 31P NMR in deuterated chloroform (CDCl3), respectively .Results:FTIR and ATR findings indicated that the spectra of the reaction products of HA and the self-etching primers containing carboxylic acids revealed the typical stretching bands of carboxylic salts, besides the separate hydroxyl groups and the primers' characteristic bands. After the spectra of the reaction products were subtracted by either corresponding primer or HA , they revealed the typical stretching bands of carboxylic salts. Furthermore, the typical stretching bands of the primer didn't disappear even after the HA or primer spectrum subtraction .After the spectra of the reaction products of HA and the self-etching primers containing phosphoric acid esters were subtracted by those of primer, there still existed the typical bands of primers such as some carbonyl groups (C=O), double bands (C=C) etc., and of HA such as the phosphoric groups (P-O, P=O) in the reactions. After the spectra of the reaction products were subtracted by the spectrum of the HA, they revealed some changes of the phosphoric groups from 1300 cm-1 to 800 cm-1.31P NMR findings indicated the phosphorus-31 chemically shifted after M2P reacting with HA or Ca(OD)2 .The major peaks of M2P interacting with HA were at therange of 0.1956- 0.6738 ppm, while M2P interacting with Ca(OD)2 were at the range of 0.5315-1.2978 ppm.The spectrum of the supernant solution separating from the reaction of M2P'with Ca(OD)2 detected in deuterium chlorform showed two main peaks from -0.8856 to 0.6130 ppm while five peaks in the solid reactions from -1.3464 to 0.2597 ppm.The spectrum of the supernant solution separating from the reaction of M2P with HA dete...