Effect Of Two Antioxidants On Immediate Bond Strength Of Resin Cement To Bleached Enamel

When the tooth color is abnormal,the combination of tooth bleaching technology and CAD/CAM ceramic veneer technology is one of the better choices to reduce the number of visits and achieve the best restoration effect.However,it has been found that the use of bleaching agents can reduce the bond strength between enamel and resin,especially immediately after bleaching.The most important reason is related to the oxygen generated by peroxide in bleach gel and the residual oxygen free radicals in dental tissue.Antioxidants can effectively neutralize the residual oxides and oxygen free radicals in enamel,reduce the damage to enamel structure,restore the redox potential in the binder and ensure the normal polymerization of resin.At present,there are many studies on the application of sodium ascorbate,and some research foundations have been obtained.However,there are great differences in the optimal time for the application of antioxidants to restore the bond strength between bleached enamel and resin.In order to find a more effective and safer antioxidant,we carried out the following experiments.Objective:The effect of 10%sodium ascorbate solution and 5%proanthocyanidins solution on the micro-tensile bonding strength of resin cement(Porcelain veneer bonding suit)to bleached enamel was compared,and to find the optimal treatment time of antioxidants.Methods:Twenty-four human premolars were extracted in recent one month.Cut the teeth into cheek-tongue two equal parts in proximal and distal directions and cut off the root 1mm below the enamel-cementum boundary.After uniformly grinding the enamel of about 0.5mm in the middle of cheek or tongue,the enamel plane of about 5mm×5mm was prepared.Grind:ing and polishing teeth with sandpaper.The experiment was divided into four groups:two control groups and two experimental groups.Two control groups included non-bleaching-bonding group(positive control group)and bleaching-bonding group(negative control group);Two experimental groups included bleaching-10%SA solution treatment-bonding group and bleaching-5%PC solution treatment-bonding group,which were further divided into three subgroups according to the treatment time(30,60,120minutes).After the preparation of enamel-resin cement bond specimens by grouping,micro-tensile specimens with the size of 1mm × 1mm × 8mm were prepared.The specimens were tested for micro-tensile bond strength,the fracture interface type was observed by stereomicroscope,the bonding interface was observed by scanning electron microscope,and statistical analysis of the data.Result:All micro-tensile bond strength test specimens had a high percentage of adhesive failures.The MTBS value of 10%SA treatment group was significantly higher than that of 5%PC treatment group(P<0.05).With the prolongation of antioxidant treatment time,the MTBS value significantly increased(P<0.05).The MTBS values of 10%SA treatment for 30,60 and 120 minutes were significantly different(P<0.05).There was no significant difference in MTBS between 30 min and 60 min of 5%PC treatment(P>0.05),but there were significant differences between them and 120 minutes treatment(P<0.05).There was no significant difference in MTBS values between 30 min of 5%PC treatment and negative control groups(P>0.05),but there was significant difference in MTBS values between the control groups and all other groups(P<0.05).Scanning electron microscope showed that the bonding interface of bleached enamel and resin cement was loose,cracks appeared and linear.With the prolongation of antioxidant treatment time,the interface became denser,cracks disappeared and resin protrusions formed.The bonding degree of 10%SA treatment group was generally stronger than that of 5%PC treatment group.Conclusion:1.Teeth bleaching can significantly reduce the bond strength of resin cement to enamel.2.The application of 10%sodium ascorbate and 5%proanthocyanidins can significantly improve the bond strength of resin cement to bleached enamel.3.The effect of 10%sodium ascorbate on the bond strength of resin cement to bleached enamel was significantly higher than that of 5%proanthocyanidins.4.The bond strength of resin cement to bleached enamel can be significantly improved by prolonging the use time of antioxidants.At least 120 minutes should be used.