Study Of Chemical Interaction Between Acidic Monomers And HAP And Its Effects On Bonding Performance To Dentin

Objectives:In order to understand the bonding and degradation mechanisms at the biomaterial-hard tissue interface thoroughly and provide guidance for clinical selection and use of adhesives.We studied the chemical interaction between the acidic monomers in four different adhesives and HAP,the main composition of dentin.And then evaluated the effects of the chemical interaction on short-term in vitro performance of the four adhesives bonded to human dentin.Material and methods:Part I: Dentin disks of(10*8*1mm)were prepared,and then Clearfil SE Bond(CSE)that contains 10-MDP,Scotchbond Universal(SU)that contains 10-MDP,Optibond XTR(OX)that contains GPDM,and Adper Easy One(AEO)that contains 6-MHP were applied to dentin surface for 20 s.Chemical interaction between the functional monomers and dentine were characterized chemically,using thin-film X-ray diffraction and ultrastructurally,using scanning electron microscopy.The hydrophilicity of each acidic functional monomer was assessed by a Chemical Structure Drawing software(ChemBioDraw Ultra),and then the effects of the structure and hydrophilicity of acidic monomers on the chemical interaction between the functional monomers and dentine were analyzed.Part II: The adhesives were applied onto coronal dentin surfaces and built up with resin composite.Specimens were then longitudinally sectioned perpendicular to the bonding interface to obtain resin-dentin bonded sticks and slices.The sticks were used to evaluate the mechanical property of the adhesives,either immediately or after thermo-cycling(5–55℃)for 5000 cycles recorded as microtensile-bond-strength(μTBS).The slices were used for interfacial nanoleakage evaluation before thermo-cycling and after under SEM.Results:Thin-film X-ray diffraction showed that both CSE and SU revealed 10-MDP–Ca nano-layering at the adhesive interface,but with different intensity when reacted with dentin for 20 s.No characteristic peaks that may be assigned to the products of chemical interactions between the functional monomer and dentine in the OX and AEO groups appeared.10-MDP presented the lowest hydrophilicity,with GPDM the highest and 6-MHP in between.OX that contains GPDM demineralized the dentin surface more intensely,and the bonded specimens of OX showed considerably longer resin tags formation.The highest μTBS was initially seen in OX>SU>CSE>AEO.But a significant drop of the μTBS(p<0.05)was observed for AEO after thermal-cycling for 5000 cycles,and also a drop for OX though without significant differences after aging(p>0.05).OX and AEO showed significantly increased nanoleakage after aging.While both the μTBS and nanoleakage remained stable for CSE and SU that contains 10-MDP before and after thermal-cyling(p>0.05).Conclusions:In summary,the chemical structure and hydrophilicity of the acidic monomers influenced its chemical bonding potential to HAP.Functional monomers with high hydrophilicity show limited chemical bonding potential to HAP,resulting a severe surface-decalcification effect.For the same kind of acidic monomers,the higher the concentration,the more intensely of the chemical interaction with HAP.The stable chemical bonding between10-MDP and Ca of HAP is advantageous for long-term durability of adhesive-dentin bonds.