In Vitro Study On The Prevention And Remineralization Of Enamel Demineralization By Clinpro^TMXT Varnish

Purpose:Clinpro^TMXT Varnish is a new generation of glass ionic polymer modified by light-cured resin,Its effect of assisting in remineralization and enhancing enamel prevention is not clear yet,which is worthy of further study by simulating real clinical conditions.In this study,the effects of Clinpro^TMXT Varnish and duraphat,a commonly used fluoride preparation,on the prevention of enamel demineralization and re-mineralization,were compared by scanning electron microscope observation,microhardness measurement,calcium and phosphorus element analysis,combined with the experimental model of p H circulation in vitro.Methods:A total of 122 premolars aged 12-21 years old were extracted for orthodontic treatment in Qingdao Municipal Hospital Affiliated to Qingdao University.Ultrasonographic cleaning,soft tissue removal and root removal were performed to make enamel blocks of 4 mm×4 mm×3 mm.Two of them were randomly selected for scanning electron microscope（SEM）observation as healthy controls,and the rest were used in two experiments.（1）In enamel protection test（experiment A）:Sixty enamel blocks were selected and randomly divided into 3 groups（n=20）.All enamel blocks in group A1 were coated with Clinpro^TM XT Varnish according to the method of application provided by the manufacturer（acid etching for 15 s,acid etching agent removal,air gun drying,evenly coating a thin layer of material in the window area with a small brush,and lighting curing for 25 s）.group A2 was the positive control group,which was repeatedly rubbed with duraphat for 1 min.The group A3 was the negative control group without any treatment.After pretreatment,three groups of samples were placed in artificial saliva.（2）In remineralization test（experiment B）:another 60 enamel blocks were taken and pre-placed in artificial demineralization fluid for demineralization for 72 h.After demineralization,they were randomly divided into three groups（B1,B2,B3）（n=20）.The pretreatment method was the same as that in the enamel demineralization prevention experiment group.After the previous treatment,the oral environment was simulated in six groups of samples A and B,and they were all treated with artificial demineralization fluid and artificial saliva alternately in p H cycle for 30 days.The surface ultrastructure of the enamel was observed by SEM,the changes of surface microhardness（SMH）of the enamel were measured by microhardness tester,and the contents of calcium and phosphorus on the enamel surface were analyzed by X-ray energy spectrum analyzer.SPSS 26.0 software package was used for statistical analysis of the data.Results:（1）In enamel protection test:The results of scanning electron microscope showed that the enamel surface of healthy control was flat and uniform.After the prevention experiment of enamel demineralization,Clinpro^TMXT Varnish group showed the interprismatic substance was widened on enamel surface,without obvious honeycomb structure,and the surface was basically complete.In the positive control group,a large number of flaky sediments were seen on the enamel surface,and honeycomb structure was partially covered,and the clear interprismatic substance shape was visible.In the negative control group,the enamel surface was obviously uneven with a small amount of irregular sediments,which showed typical honeycomb changes of enamel demineralization.Microhardness measurement results showed that there was no significant difference in microhardness between Clinpro^TMXT Varnish group and dorofluoride group after enamel demineralization prevention experiment（p=0.071）,both of which were higher than those of negative control group（p<0.05）.The pairwise comparison of microhardness difference（ΔSMH）between each group before and after the experiment showed that group A1<group A2<group A3,and the differences were statistically significant（p<0.05）.The ratios of calcium and phosphorus were in the order of group A1>group A2>group A3,and the differences were statistically significant（p<0.05）.（2）In remineralization test:The results of scanning electron microscope showed that the enamel surface of Clinpro^TM XT Varnish group was relatively flat,with scattered lamellate sediments,no obvious pit structure,and no obvious demineralization.The enamel surface of the positive control group was rough and uneven,and the pits were covered by a lot of sediments,but there were still scattered pores.The enamel surface of the negative control group showed obvious honeycomb-like structure,with deep pits on the surface,and even connected into pieces.The enamel center and interstitial morphology of the enamel column could be seen clearly.The results of microhardness measurement showed that the pairwise comparison of microhardness measured in each group after the experiment showed statistically significant differences（p<0.05）.ΔSMH is the difference of microhardness measured before and after the experiment.The pairwise comparison of SMH between each group shows that there is statistical significance in the difference between group B1>group B2>group B3（p<0.05）.The ratios of calcium and phosphorus were in the order of group B1>group B2>group B3,and the differences were statistically significant（p<0.05）.Conclusions:（1）Both Clinpro^TMXT Varnish and duraphat can prevent enamel demineralization and promote demineralized enamel re-mineralization,and Clinpro^TMXT Varnish has a better effect.（2）Clinpro^TMXT Varnish has better wear resistance than duraphat.（3）The enamel demineralization has certain limitations and cannot completely reverse the white spot lesions.It is more important to prevent enamel demineralization than to treat it.