In Vitro Study Of Er:YAG Laser And Nd:YAG Laser Applied To Tooth Bleaching

Objective:To study the difference in bleaching effect,the stability of tooth color after bleaching,and the effect of laser bleaching on the surface structure by comparing traditional medical bleaching,cold-light bleaching,Er:YAG laser,Nd:YAG laser,Er:YAG laser combined with Nd:YAG laser bleaching,the microhardness measurement and scanning electron microscope observation of the tooth tissue are carried out at the same time.This experiment will provide a certain theoretical basis for clinical application.Methods:A total of 120 premolars extracted for orthodontic treatment were randomly divided into 6 groups.Group A: no treatment;Group B: 35% hydrogen peroxide coated tooth surface;Group C: 35% hydrogen peroxide coated tooth surface + cold light bleaching;Group D: 35% hydrogen peroxide coated tooth surface + Er:YAG laser;Group E: 35%hydrogen peroxide coated tooth surface + Nd:YAG laser;Group F: 35% hydrogen peroxide coated tooth surface + Er:YAG laser,Nd:YAG laser.Measure the color parameter LAB before and after bleaching by digital colorimeter,and analyze the difference in bleaching effect of each group.The microhardness values before and immediately after bleaching and 28 days after bleaching were measured by micro-Vickers hardness tester,and observed under scanning electron microscope.The effect of laser bleaching on enamel surface structure was analyzed.Results:1.After bleaching,each group produced significant color changes: immediately after bleaching,group C had the most obvious change,followed by group F,and group D had the smallest color change;at 28 days after bleaching,there was no significant difference in bleaching effect between the groups(P>0.05).2.The color change on the 7th day after bleaching in group D and E was higher than that immediately after bleaching(P<0.05),and there was no significant difference in color change starting from 7 days after bleaching(P>0.05);The color change of group C and F on the 14 th day after bleaching was significantly higher than that immediately after bleaching(P<0.05),and there was no significant difference in color change starting from14 days after bleaching(P>0.05).3.The microhardness value of group C immediately after bleaching and 28 days after bleaching was lower than that before bleaching(P<0.05),There was no significant difference in the microhardness values of groups D,E and F immediately after bleaching,28 days after bleaching and before bleaching(P>0.05).4.Scanning electron microscope observation: There were more cracks in group C,with more dimples and micropores on the enamel surface,and enamel demineralization;the surfaces of groups D,E,and F were smooth,without obvious melting and cracks.Conclusion:1.Both laser bleaching and cold light bleaching can achieve good bleaching results.2.Immediately after bleaching,Er:YAG laser combined with Nd:YAG laser bleaching has no significant difference compared with cold light bleaching,while Er:YAG laser bleaching and Nd:YAG laser bleaching alone do not show superiority;7days after bleaching,the effects of laser bleaching and cold-light bleaching in each group tended to be consistent.3.The color of Er:YAG laser bleaching and Nd:YAG laser bleaching alone will be stable in 7 days after tooth bleaching,while the color of Er:YAG laser combined with Nd:YAG laser bleaching and cold light bleaching will be stable in 14 days after tooth bleaching.4.Laser bleaching in each group has less effect on tooth microhardness than cold light bleaching.5.Scanning electron microscopy observed that the enamel surface after laser bleaching in each group was smoother than cold-light bleaching,and there was no obvious melting and cracking.