Identification Of MMPs In Different Dentinal Substrates And Their Effects On The Degradation Of Bond To Dentin

The development of dental bonding technology makes variety of teeth defectsrestoration become possible. Because of the advantages of minimally invasiverestoration and aesthetic restoration, it has become an important researchingcontent in dentistry. Solid, long-term adhesion between enamel or dentin anddental prosthetic material is the key to the success of dental adhesive restoration.Because of the particularity of the dentin structure and composition, adhesionbecomes one of the difficult points and hot spots in the field of dental adhesion.In the past20years, the adhesive materials and bonding methods are undergoingrapid development. And the immediate bonding strength of the currently existingdentin bonding materials has significantly improved, which is reported up to50-70MPa. But after used in the complex oral environment, prosthetic restorationwould gradually appear coloration of the prosthesis edge, secondary caries, andeven the prosthesis off. Studies showed that in vivo dentin bonding strength ofthe adhesive interface decreased significantly in3to5years, and in vitroexperiments dentin bonding strength even decreased significantly after sixmonths, which meant degeneration in the dentin adhesive interface occurred.Once degeneration occurred, it would cause reduction of fitness of restorationmargin and loss of retention, which ultimately led to failure of adhesiverestoration. Therefore, the defects of bonding durability had become an importantscientific problem to be solved, which would constrain the development of oralbonding technology. The study showed that dentin contained endogenous proteolytic enzymes-Matrix Metalloproteinases, MMPs. The enzyme could degrade all extracellularmatrix. About90%of the composition of dentin organic matrix is type Ⅰcollagen fibers. And the dentinal matrix metalloproteinases may degrade type Icollagen fibers in the dentin adhesive interface, to participate in the degenerativeprocess of the dentin adhesive interface. The dentin contains a variety of MMPs,and each MMP has a specific degradation substrate and the mode of function.Now the distribution of MMPs in dentin, as well as the role in and the mechanismof degeneration process in the bonding interface is still lack of sufficient research.The purpose of this study is to research on the distribution of dentinal MMPs indifferent types dentin matrix and its correlation with the durability of dentinadhesion, and to explore the types and the role of the dentinal MMPs involved indentin interface degeneration. It also searches for a reliable and effective way toinhibit degeneration in dentin interface, and lay the theoretical foundation ofimprovement the adhesion durability.1. Methods1) Using immunohistochemical staining and liquid chip to detect the type anddistribution of MMPs in normal and sclerotic dentin.2) Using thermal cycling and long-term soak in artificial saliva to simulateaging conditions, in order to detect degeneration in the aging treated dentininterface and variation in the content of MMPs.3) To evaluate the bonding strength with the micro-shear bonding strength test,to detect and analyze nanoleakage in adhesive interface by FE-SEMcombined with EDX, and to detect degradation of collagen and activity ofMMPs in the bonding interface through Cross-linked carboxyterminaltelopeptide of type I collagen reaction, in order to investigate of different adhesive systems and the relationship between dentinal MMPs and dentinadhesive durability.2. Results1) Five kinds of MMPs of MMP-1, MMP-2and MMP-3, MMP-8and MMP-9both existed in normal dentin and sclerotic dentin.2) In the normal coronal dentin, the distribution of dentinal MMPs: MMP-1,MMP-2and MMP-3, MMP-8and MMP-9both decreased from near pulpcavity to dento enamel junction. In the same layer of dentin, the contents ofthe five dentinal MMPs decreased as MMP-8> MMP-2> MMP-9> MMP-3>MMP-1.3) Along with the increase of age, the human dentinal MMP-2and MMP-3decreased.4) The contents of dentinal MMP-8and MMP-9in the sclerotic dentin weresignificantly higher than those in normal dentin, which suggests dentinalMMP-8and MMP-9may closely relate to the formation of non-carioussclerotic dentin.5) After aging treatment, the decreasement of bonding strength and thedegradation of collagen in deep-dentin were both more significant than thosein superficial dentin. It suggested that the degeneration of dentin interface indeep dentin was more serious than that in superficial dentin, which mayrelate to the differences of dentinal MMPs distribution.6) After aging treatment, adhesive degeneration exited both in the dentininterface of the total etch adhesive Single Bond2and self-etching adhesiveS3Bond adhesive. Dentinal MMPs may involve in the degeneration ofadhesive interface of the Single Bond2group. But their roles in thedegeneration of the adhesive interface of the S3Bond group were still not sure. After treatment of adhesive, the contents of collagenase MMP-8andgelatinase MMP-2, MMP-9decreased significantly along with the aging time,suggesting that they may be involved in the degeneration of the dentinadhesive interface.7) Using MMP-8inhibitors could increase adhesion durability of dentinadhesion interface, and there were not significant differences betweenMMP-8inhibitors and broad-spectrum MMPs inhibitor chlorhexidinesolution, which suggested that the collagenase MMP-8may play a leadingrole in the degeneration in the dentin adhesive interface.