| Objective:To evaluate the effect of different bleaching methods on the microhardness of white-spot lesions of the enamel and scanning electron microscope observation and evaluate the effects of microleakage on the white-spot lesions of the enamel treated with different bleaching methods and evaluate the effectiveness of different bleaching methods on the white-spot lesions of the enamel using optical coherence tomography,to evaluate its feasibility for monitoring the therapeutic effects on the white-spot lesions.Methods:One hundred and twenty sound premolars extracted for orthodontic reasons were selected and cut for enamel blocks(approximately 4 mm ×4 mm ×2 mm)in the buccal surfaces of the crown.The samples were covered with acid-resistant varnish(except for the buccal surfaces)and immersed in demineralization solution for 18 days to establish the in-vitro research models of white spots lesions in enamel.In Experiment 1,48 demineralized enamel blocks were randomly divided into 4 groups(n=12).The samples in groups A to D were Group A was given demineralization only.The specimens in groups B,C and D were treated with 40%hydrogen peroxide,infiltrated resin and 40%hydrogen peroxide combined with infiltrated resin respectively.After treatment for all samples,the enamel blocks were embedded in an epoxy resin,except the buccal surfaces.Eight samples in each group were randomly selected and measured for the microhardness values of the enamel surface by a microindentation hardness tester.The records were analyzed by the SPSS 26.0 software.The remaining four samples in each group were cut longitudinally,and the ultrastructural changes of enamel samples in each group were observed by scanning electron microscope after regular ethanol gradient dehydration,drying and gold spraying.In Experiment 2,72 demineralized enamel blocks were randomly divided into 4 groups(n=18).Group A was given demineralization only.The specimens in groups B,C and D were treated with 40%hydrogen peroxide,infiltrated resin and 40%hydrogen peroxide combined with infiltrated resin respectively.After treatment for all samples,the enamel blocks were embedded in an epoxy resin,except the buccal surfaces.8 samples in each group were randomly selected,OCT was applied to observe the optical changes of the surface of enamel and the ultrastructural changes of enamel samples in each group were observed by scanning electron microscope,according to the OCT scanning results to calculate the demineralization depth of enamel samples in each group.10 samples from group A-D were immersed in 2%methylene blue solution for 2 hours.Microleakage was evaluated by light microscopy.Data were analyzed by using the Kruskal-Wallis test and Bonferroni post-hoc correction.Results:1、The microhardness values(kg/mm2)of the samples in each group were(214.99±31.70),(250.66±33.64),(312.42±18.01)and(286.53±26.65),respectively.One-way ANOVA showed that different bleaching methods had significant differences in the microhardness of enamel white spots(F=18.213,P=0.000).The microhardness values of the samples in group A was the lowest,with the highest in group C.2、SEM observation showed that the enamel surface treated with penetrating resin was more flat and dense.3、Under stereomicroscope,the microleakage in group A was the most serious,followed by that in group B.There was almost no microleakage in group C,The values for Groups D and C did not significantly differ(P>0.05).4、OCT showed that the light scattering characteristics of enamel surface changed in all group,and the bright layer was formed,but the thickness of bright layer in groups C and D was significantly lower than that in groups A and B(P<0.05).Conclusion:1、Resin infiltration or 40%hydrogen peroxide combined with infiltrated resin can improve the surface microhardness and flatness of the white-spot lesions in enamel.2、Resin infiltration therapy can protect enamel and reduce microleakage.3、The non-invasive OCT can be used as a better evaluation method for the diagnosis and treatment of the white-spot lesions of the enamel. |
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