| Nowadays,people’s demand for maxillofacial beauty is increasing day by day.Dental aesthetics,as one of the important components,is gaining more and more attention."red lips and white teeth" are pursued by people,but some exogenous or endogenous factors often make teeth show existing color spots or patchy appearance,which seriously affect the beauty of teeth.The color stains on the surface of some teeth can be removed by cleaning and sandblasting,while dental fluorosis,aging discolored teeth and leukoplakia lesions such as chalk plaque and early enamel caries after orthodontics need further treatment.In the era of people’s pursuit of non-invasive treatment,cold light whitening and infiltration resin emerge as the times require,cold light whitening can improve tooth coloring,infiltration resin can improve chalk spots,the combined application of the two will lead to more uniform changes in aesthetics.ObjectiveIn this experiment,by analysing the surface structure and microhardness of enamel,measuring the color changes at different time points before and after treatment,and investigating the recoloring ability of each group by immersing in coffee solution in the later stage,the effects of cold light whitening,infiltration resin and their combined application on the structure and aesthetic properties of enamel were further explored,which were hoped to provide more adequate theoretical basis and guidance for clinical practice.MethodsIn the Department of Oral and Maxillofacial surgery of the first affiliated hospital of Zhengzhou University,131premolars extracted for orthodontic treatment in recent 3 months were collected.The surface pigments,dental calculus and residual soft tissue were removed.The samples were examined by stereoscopic microscope to ensure that there were no caries,microcracks or other surface defects.Store them in the refrigerator at 4℃ in 0.9%NaCl solution until the beginning of the experiment.The experiment was divided into four groups:group A was blank control group,group B was cold light whitening group,group C was infiltration resin group,and group D was cold light whitening+infiltration resin group.27 of 131 premolars were randomly selected to observe the enamel structure by scanning electron microscope.The buccal part was cut in the middle of the dental crown and maxillofacial region along the proximal and distal direction,and 3 samples were randomly selected for acid etching with hydrochloric acid etching agent in the resin set and observed immediately.The remaining 24 samples were randomly divided into groups A,B,C and D,and were observed by scanning electron microscope immediately and 2 weeks after treatment,that is,3 samples at each time point in each group,and the morphology of enamel surface was analyzed and compared.64 premolars were randomly selected from the remaining 104 premolars for microhardness measurement.About 3 ×3× 2mm enamel-essence samples were prepared from the dental crown,tongue,palate and buccal surface,respectively.The microhardness of the tongue and palate samples were measured at baseline,and the results showed no difference.The buccal samples were randomly and evenly distributed to groups A,B,C and D,and the microhardness was measured immediately and 2 weeks after treatment,that is,8 samples at each time point in each group.Color measurement and recolor experiments were performed on the remaining 40 teeth with CIELAB system.The baseline value of L*was measured in advance,and there was no difference in the results.Groups A,B,C and D were randomly divided into groups A,B,C and D with 10 in each group.The apical foramen was closed with fluid resin.The values of L*,a*,b*and ΔE on the buccal surface of teeth were measured before and immediately after treatment,1,3,5,7 and 14 days after treatment.After 14 days,the samples of each group were immersed in coffee solution for one week,and the values of L*,a*,b*were measured again,and the color difference ΔE was calculated and compared.Results1.The results of scanning electron microscope showed that the surface of normal enamel was flat and uniform,the surface of enamel was smooth under cold light whitening immediately under low power microscope,there were microporous defects and white granular mineral deposits under high power microscope,and the surface of enamel was uniform and smooth at 2 weeks.close to normal enamel.Immediately and 2 weeks after resin infiltration and combined treatment,there was no significant difference in the enamel surface,but they were flat.the resin covered on the enamel surface could be seen under high power microscope,and several micropores could be observed.2.Microhardness measurement results:immediately after treatment,the microhardness of the whitening group increased significantly,compared with the other three groups,the difference was statistically significant.Meanwhile,the microhardness of the infiltration resin group was increased with no significant difference compared with the control group,and there was no statistical difference between the combined group and the control group.Besides,after 2 weeks of treatment,there was no significant difference between the three experimental groups and the control group.3.Color change and recolorization:before staining,the color of the control group was stable;while in the whitening group,the L*value increased significantly,the a*and b*values decreased significantly,and they remained stable after 3 days,meanwhile ΔE reached the maximum after stabilization which was significantly different from that of the control group;in the infiltration resin group,the value of L*decreased with no significant difference compared with the control group after stabilization,and the values of a*,b*did not change significantly,as for the value ofΔE,there was no significant difference compared with the control group on the 5th and 7th days,but there was significant difference 2 weeks later;in the combined group,the L*value increased significantly and the values of a*,b*did not change significantly,but remained stable after 3 days,meanwhile,for the ΔE,there was no statistical difference compared with the whitening group.After staining,the L*value decreased and the a*,b*value increased in all groups,among them,the most significant L*value reduction was observed in the whitening and combination groups,The L*value modification in the combination group was larger than that in the whitening group,but there was no statistical difference;the values of a*,b*in the whitening group increased the most,which were statistically different from those in the other groups;the value of ΔE for whitening group and combination groups was larger,and the latter was greater than the former,but there was no statistical difference;there was no significant difference in ΔE between the infiltration resin group and the control group.Conclusion1.The cold light whitening treatment can cause slight demineralization of enamel surface immediately,with mineral deposits at the same time,and after two weeks it is close to normal.While the infiltration of resin and the combined treatment have no significant effect on the enamel surface structure.2.Cold light whitening can immediately improve the microhardness of the enamel surface and return to normal after two weeks;While there was no significant change in the microhardness of infiltration resin and combined treatment.3.Cold-light whitening and combined treatment can significantly improve the whiteness of teeth and produce significant color changes,but it is easy to recolor after dyeing.While infiltration resin has little effect on tooth color. |
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