| Objective:The effects of bacterial invasion and artificial saliva immersion on bonding strength,nanoleakage value and fracture type of sound dentin to glass ceramics bonded specimens under three kinds of resin cenments were studied.The adhesive durability of three kinds of resin cemnets was evaluated to provide the basis for the material selection of repair clinic.Methods:108 intact caries-free third molars were removed by high-speed diamond grinding under the condition of flowing water cooling to expose the axial surface of dentin and remove the residual dentin around them to obtain dentin specimens.108 dentin specimens were divided into three groups by random digital table method,and 36 dentin specimens in each group were bonded with three kinds of resin cements:Variolink N ? multilink N ? RelyX Unicem and domestic glass ceramic blocks,respectively.Thirty-six specimens of each type of resin cements were divided into three groups: bacterial invasion group?artificial saliva group and immediate test group and each treatment group 12 bonded specimens.Six bonded specimens were selected from each treatment group and their shear forces were measured by universal testing machine,and then their bond strength was calculated.The fracture surface morphology was observed under 40-fold stereoscopic microscope,and the fracture types were recorded.The remaining 6 specimens were stained with silver in 50%(w/v)ammoniated nitric acid solution.The leakage of silverparticles on the bonding surface was observed by using the back scattering model of thermal field emission scanning electron microscope and the nanoleakage classification was calculated.Results:As far as bonding strength is concerned,two-way ANOVA shows that the type of adhesive is P<0.05 and the aging mode is P<0.05,which indicates that the two factors have influence on the bonding strength.The immediate bonding strength of Variolink N group,Multilink N group,RelyX Unicem group(8.44±1.18)MPa,(2.44±1.81)MPa,(2.31±1.66)MPa respectively,The bond strength of Multilink N group and RelyX Unicem group was significantly lower than that in Variolink N group.The bond strength of Variolink N in immediate adhesion group,artificial saliva immersion group and bacterial invasion group was(8.44±1.18)MPa,(3.24±2.16)MPa,(2.05±0.68)MPa,respectively.The bond strength between bacterial invasion group and artificial saliva immersion group was significantly lower than that immediately(P<0.05),but there was no significant difference in other groups(P>0.05).Compared with the immediate test group,the nanoleakage of Multilink N in artificial saliva aging did not increase significantly at 6months(P>0.05).the nanoleakage of Variolink N and RelyX Unicem increased after two kinds of aging(P<0.05).However,there was no significant difference between the two aging methods(P>0.05).Conclusion:1.After bacterial invasion,the bond strength of the three resin bonding systems all decreased and the Variolink N decreased significantly.2.After immersion in artificial saliva,the bond strength of Variolink N and RelyX Unicem decreased and Variolink N decreased significantly,but the bond strength of Multilink N increased.3.The nanoleakage of the three resin bonding systems increased after bacterialinvasion,indicating that the existence of Streptococcus mutans in the oral cavity would affect the interfacial sealing of resin dentin bonding interface.4.The nanoleakage of the three resin bonding systems increased after artificial saliva immersion,but the increase of Multilink N was not significant.5.No nanoleakage was found in the interface between resin bonding layer and ceramic block,indicating that the surface treatment of glass ceramics interface by hydrofluoric acid etching and silane coupling agent is an effective method to improve the bonding effect. |
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