The Impacts Of Matrix Metalloproteinases Inhibitors Of The Dentin Bonding Of Self-etching Adesives

Objectives:The immediate bonding effectiveness of resin-dentin is quite favorable, whereas it's bond strengths drops dramatically with time.Many studies have shown that hydrolytic degradation of dentin collagen matrices and/or resin elution in aged resin-dentin interfaces result in reduced long-term bond strength.Matrix metalloproteinases inhibitors(MMpls) provide a potential pathway for inhibiting collagen degradation in bonding interfaces thereby increasing dentin bonding durability. Galardin is a synthetic peptoid MMpls, which was used as a kind of drug to cure corneal ulcers. Recently Lorenzo Breschi found that applying galardin to phosphoric acid-etched dentin prior to the etch-and-rinse adhesives had no effect on immediate bond strength,while it significantly decreased the bond interface'degradation and lowered the loss of bond strength. But how galardin as a pretreatment prior to the self-etching adhesives influence on the resin-dentin bonds has not been confirmed.In this experiment,I chose two kinds of MMpls:clorhexidine digluconate(CHX) and galardin,which were applied to dentin prior to the self-etching adhesives,and tested the efficacies of them on the mechanical and morphological preservation of aged resin-dentin bonding interfaces through microtensile bond strength test and observation with field emission scanning electron microscope.Materials and methods:Fifteen freshly extracted and non-carious human third molars which had integrity configurations were selected in stamotological surgery and later stored in normal saline(NS) that contained 0.02% NaN3 at 4℃.The surfaces of middle dentin were exposed with a slow speed diamond saw (Huayan,Shanghai, China). Later bonding surfaces were sequentially ground (600-grit SiC abrasive paper)under a stream of water for 60s so that surfaces would be flat. Prepared dentin surfaces were then carefully washed with distilled water and placed in distilled water in an ultrasonic cleaner (QT3120,Ruipu,Tianjin,China;output power,80W; frequency, 40kHz) for 15 min for removal of sticky residual surface contaminants and smear plugs.Teeth were randomly assigned to the following treatments(N=5). Groups A:dentin surfaces were treated with 115μL distilled water for 30s, blot-dried and bonded with Panavia F2.0 adhesive system(control).Groups B:dentin surfaces were treated with 115μL 22 mM clorhexidine digluconate(CHX) for 30s, blot-dried and bonded with Panavia F2.0 adhesive system. Groups C::dentin surfaces were treated with 115μL 0.2 mM galardin (water solution) for 30s, blot-dried and bonded with Panavia F2.0 adhesive system. Panavia F2.0 adhesive system was applied in accordance with manufacturer's instructions.Composite resin crowns(Tokuyama Dental)were constructed.After stored in artificial saliva at 37℃for 24 h,these specimens were fixed on the a slow speed diamond saw,and resin-dentin sticks with cross-sectional area of approximately 1.0mm2 were obtained. Randomly in every team Sticks were divided in two equal secondary groups according different storage time:24 h or 3 mon.the former 10 sticks every team were stressed until failure with a simplified universal testing machine at a crosshead speed of 0.5mm/min. The data for each stick were subjected to explore and univariate analysis of varianee.Sticks'failure modes were evaluated.The fractured surfaees were examined by scanning eleetron microscope (SEM).The data were analyzed with one-way ANOVA (tested variable was method of pretreatments) by SPSS 17.0. Pairwise comparison was used to analyze the differences for each group, Statistical significance was set at P<0.05.Results:1.Microtensile bond strength test:ANOVA analysis showed that after 24 hours of water storage, there were no differences between the bond strength of control versus experimental groups(control group:17.30±3.57Mpa; CHX group:17.62±3.59Mpa; galardin group:17.37±3.66Mpa; P> 0.05).Conversely, after 3 months of storage in artificial saliva at 37℃, the groups showed significant differences(control group:9.73±3.15Mpa; CHX group:12.62±2.55Mpa; galardin group:15.61±3.62Mpa; p<0.05).The bond strengths of control group decreased approximately 43.76%,while CHX group and galardin group respectively decreased 28.38% and 10.13%.It's proved that The use of MMpls(CHX and galardin)had no effect on immediate bond strength,while the two inhibitors significantly decreased bond degradation after 3 months(p< 0.05),and the effect of inhibition of galardin was much stronger than CHX's.2.SEM observation:2.1 After 24 hours of water storage:Control group:failure in adhesive, surface was full of adhesive,no dentin structures could be seen.CHX group:failure in adhesive, surface was full of adhesive,no dentin structures could be seen.Galardin group:failure in adhesive, surface was full of adhesive,no dentin structures could be seen.2.2 After 3 months of water storage:Control group:mixed failure, we could found larger gaps between resin tags and dentin tubule walls and some dentin tubules almost were completely exposed, peritubular collagen fiber network structure had visible damage and even damage to fracture.CHX group:mixed failure,small gaps between resin tags and dentin tubule walls could be seen. peritubular collagen fiber network structure had a porous morphology.Galardin group:mixed failure,compare with CHX group,the gap between resin tags and dentin tubule walls seemed smaller,and peritubular collagen fiber network structure had a porous morphology.From the morphological view,it's confirmed that MMPs inhibitor slowed the degradation of collagen in dentin hybrid layer, and galardin was more spesific than chlorhexidine when applied to dentin prior to the self-etching adhesives. It also showed Panavia F2.0 had excellent bonding properties.Conclusion:In this study, compared with CHX, specific inhibitor of MMPs galardin increased durability of dentin bonding more effectivly.the inhibition of degradation of collagen fibers protected the stability of resin dentin bonding interface; Matrix metalloproteinase inhibitors can inhibit the hydrolysis of dentin collagen fibers; indicating that a paradigmshift has occurred in adhesive dentistry. That is, that preservation of resin-bonded interfaces requires prevention of degradation of collagen fibrils in hybrid layers,which will improve resin bonded restorations'clinical long-term life.