Effects Of Novel Biphenyl Resin-based Dental Composites Containing Pchi/ACP On The Remineralization Of Human Dentin In Vitro

Dental light-curing composite resin is mainly composed of polymerizable matrix monomer,inorganic fillers,photoinitiator and other additives.Since 1960s,Bisphenol a-glycidyl methacrylate?Bis-GMA?has been used as the matrix monomer for dental light-curing composite resin due to its excellent aesthetics,clinical operation and good biocompatibility,which can meet the demands for dental restoration.It has become the most commonly used dental restorative material.But its inevitable volume contraction after curing could destroy the edge sealing of the restoration,which causes complications such as sensitive,micro leakage and secondary caries.In addition,dentin tissue has a higher ratio of the organic matrix,lower surface energy as well as the fluid in dentin tubes,which results in a discrepancy between the depth of demineralization and resin infiltration.Thus,the collagen fibers will be exposed and hydrolyzed after water absorption.Besides,the exposed collagen fibers are further degraded by matrix metalloproteinases,which weaken the bonding strength between the adhesive and dentin.Therefore,finding effective methods to maintain the integrity of the hybrid layer is an important issue.This study aims to design and synthesize a new dental light-curing composite resin containing phosphorylated chitosan/amorphous calcium phosphate complex?Pchi/ACP?,hoping to achieve the function of remineralization of apatite-defected dentin at a certain proportion.3,3',5,5'-tetramethyl biphenyl epoxy acrylate?TMBPEA?resin monomer was synthesized in our previous study.Compared with Bis-GMA,TMBPEA has better mechanical properties and lower polymerization shrinkage due to the presence of biphenyl structure.Therefore,in this experiment,TMBPEA was used as the matrix monomer.Methods:Firstly,Pchi/ACP nano-complex was synthesized,which was added to TMBPEA light-curing composite resin,and SiO₂ nano/micron mixed particles were added as reinforcing filler to prepare a new dental bioactive composite resin system.According to the different incorporation of Pchi/ACP,the experiment was divided into three experimental groups and one control group.The mechanical and chemical properties of the samples in each group were tested.Then,the dentin demineralization model was prepared,and each group of the materials was closely contacted with the demineralized dentin slabs.After soaking in simulated body fluid for 4 weeks,the dentin slabs were analyzed by SEM and EDS.Results:?1?The results of mechanical properties showed that the flexural strength,elastic modulus and Vickers hardness of the composite resin decreased with the increase of Pchi/ACP content.There was no significant difference between the flexural strength of the material containing 15 wt%Pchi/ACP and that of the control group containing no Pchi/ACP.In addition,there were significant differences between the other groups The elastic modulus and Vickers hardness of the experimental groups were both significantly lower than that of the control group.And there were significant differences between the other groups in terms of the elastic modulus and Vickers hardness.The flexural strength of each group conformed to ISO 4049.?2?The results of contact angles showed that the value of each experimental group was significantly different from that of the control group,and the contact angle gradually decreased with the increase of Pchi/ACP content.?3?The results of Ca ion release concentration showed that,at each time point,the higher the content of Pchi/ACP,the higher the Ca²⁺release concentration.Within 14 days,the Ca²⁺release concentration of the composite resin containing 35 wt%and 25 wt%Pchi/ACP was positively correlated with the time.After the 14th day,the Ca²⁺release concentration decreased and gradually stabilized.?4?The results of dentin remineralization showed that the dentin surface treated with the composite resin containing Pchi/ACP showed flake apatite deposition,and most of the dentin tubles were sealed by newly formed apatite.Meanwhile,with the increase of Pchi/ACP content,apatite deposition on the dentin surface increased,while almost no apatite deposition was observed in the control group.EDS results showed that with the increase of Pchi/ACP content,the contents of Ca and P elements on the dentin surface also increased,and there was almost no Ca and P on the dentin surface of the control group.Conclusion:The TMBPEA composite resin containing Pchi/ACP has the potential for Ca²⁺release and remineralization of dentin,which is a promising biological material.