In Vitro Study Of Er:YAG Laser Combined With Bioactive Glass On Enamel Remineralization After Interproximal Enamel Reduction

Objective:Interproximal enamel reduction is an invasive method used during orthodontic process,which may increase the risk of demineralization and proximal caries.In this study,the effects of bioactive glass,CPP-ACP,Dole fluoro,Er:YAG laser and Er:YAG laser combined with bioactive glass on enamel remineralization after interproximal enamel reduction were investigated by establishing an interproximal enamel reduction model in vitro p H cycling.This study laid an experimental foundation for dental caries prevention measures after interproximal enamel reduction in clinical orthodontics.Methods:108 interproximal enamel reduction specimens were prepared and randomly divided into 6 groups(Source of isolated teeth: The premolar was extracted for orthodontic treatment in the Department of Oral and Maxillofacial Surgery,Stomatological Hospital of Jilin University.The patient was 18-25 years old and had given informed consent and signed the informed consent,which was in line with the review and approval of the Ethics Committee of Jilin University.): group A(blank group),group B(toothpaste group),group C(Dole fluoro group),group D(bioactive glass group),E group(Er: YAG laser group),F group(Er: YAG laser combined with bioactive glass group),each with 18 specimens.Before remineralization and p H cycling,each group randomly selected 6 specimens to test the enamel surface microhardness value,and then returned to each group after the test.They were treated with bioactive glass,CPP-ACP,Dole fluoro,Er: YAG laser and Er: YAG laser combined with bioactive glass.Among them,Dole fluoro and Er: YAG laser were used only once before the p H cycling,meanwhile the bioactive glass and CPP-ACP used 2 times a day within the p H cycling for 30 days.Vickers Microhardness tester(SMH)was used to detect the surface hardness of tooth enamel,scanning electron microscope(SEM)was used to observe the surface morphology of enamel,X-ray energy dispersive spectrometer(EDS)analysis was used to detect the mass ratio and molar ratio of calcium and phosphorus on the enamel surface,and then the depth of demineralization was observed by inverted fluorescence microscope(IFM).Results:1.SMH showed: before the PH cycling,the difference in microhardness values of each groups had no statistically significant;after the p H cycling,group F had the highest microhardness value(307.83±12.54),followed by group D(230.17±11.65),Group C(193.33±13.92),Group E(189.83±7.83),Group B(175.50±7.37)and Group A(139.83±6.55);Before and after the p H cycle,the micro hardness difference of group F was the smallest,and that of group A was the largest.Except for the micro hardness difference between group C and group E,there was no statistical significance(P > 0.05),and the other groups had significant differences(P < 0.05).2.SEM showed: In group A,irregular demineralization pores and cracks could be seen on the enamel surface,and the enamel column and interstitium were dissolved and destroyed.In group B,there were a small amount of point-like and blocky high-density minerals on the enamel surface,which was unevenly distributed,and there were still many pores and cracks formed by demineralization.In group C,there were more granular and high-density minerals on the enamel surface,which were scattered or concentrated in clusters.At high magnification,the demineralization pores were significantly less than those in group B.In group D,the enamel surface was rough and covered with many pointlike and massive high-density minerals with large volume.At high magnification,fine pores were observed among the minerals.In group E,the surface of tooth enamel melted to form a shallow pit-like structure,and some pores were observed at the bottom of the pit.In group F,there were a large number of large point and massive high-density minerals on the enamel surface,which were distributed in flakes.No trace of laser melting was observed.Under high magnification,the pores between minerals were significantly less than those in group D.3.EDS showed: All the groups contained C,O,Na,P,Ca elements,and group C contained F elements in addition to the above 5 elements.Group D and F also contained the above 5 elements along with Si element.The Ca/P mass ratio and molar ratio were the highest in group F,followed by group D,C and the lowest in group A.The Ca/P mass ratio and molar ratio in F group were significantly higher than those in other groups,and the difference was statistically significant(P < 0.05).There was no significant difference between the Ca/P mass ratio between group D and C and Ca/P molar ratio between group D,C,and E(P>0.05).4.IFM showed: the thickness of the fluorescent bands in group A was the largest,followed by group B,the thickness of fluorescent bands in groups C,D,and E were similar,and the thickness of fluorescent band in group F was the smallest.The thickness of the fluorescent band in group F was significantly lower than the other groups,with statistical significance(P<0.05).There was no significant difference in thickness of fluorescent bands between group C,group D,and group E(P>0.05).Conclusion:1.Interproximal enamel reduction is successfully established.2.The SMH,SEM,and IFM results all shows that without remineralization treatments after interproximal enamel reduction,the surface hardness of tooth enamel decreased and demineralization occurs under the condition of in vitro p H cycling.3.CPP-ACP,Dole fluoro,Er: YAG laser,and BAG can effectively inhibit the demineralization of the enamel surface after interproximal enamel reduction.Among them,the inhibitory effect of BAG is the best,followed by that of Doloflin and Er:YAG laser,and the inhibitory effect of CPP-ACP is the worst.4.The combination of Er:YAG laser and BAG has a synergistic effect on inhibiting the demineralization of the enamel surface after interproximal enamel reduction.