| Objective: To investigate the immediate and long-term sealing effects of Er:YAG laser,Nd:YAG laser and Er,Cr:YSGG laser in the treatment of dentin sensitivity and their effects on the physical and chemical properties of dentin surface by establishing an in vitro model of dentin sensitivity,and to provide experimental basis for the application of three kinds of lasers in dentin sensitivity.Methods: The isolated third molars that met the inclusion criteria were collected and made into a total of 65 dentin slices with a thickness of 2mm.After gradient grinding and ultrasonic shock,they were immersed in 6% citric acid solution for 2min,and unified standard dentin sensitive in vitro models were prepared.According to different treatment methods,the samples were divided into 4 groups: blank control group(n=5),Er:YAG laser group(n=20),Nd:YAG laser group(n=20),Er,Cr:YSGG laser group(n=20).All samples were treated according to the groups.The blank control group was set as group A,and the laser group was set up in vitro simulated brushing experiment,which was divided into immediate group,1-month abrasion group,2-month abrasion group and 3-month abrasion group.They were Er:YAG laser(group B,B1,B2,B3),Nd:YAG laser(group C,C1,C2,C3),Er,Cr:YSGG laser(group D,D1,D2,D3),and there were 5 samples in each group.The microstructure of dentin surface of all samples was observed by scanning electron microscope(SEM),and the Image-Pro Plus6.0 Image analysis software measurement of dentin tubule average diameter,density,relative area,To evaluate the sealing effect of the dentin tubule in each laser group after immediate and abrasion for 1,2 and 3 months.The calcium-phosphorus ratio(Ca/P)and surface hardness of dentin surface were measured by X-ray energy spectrum analyzer and micro Vickers hardness tester,respectively.Results:(1)Comparison of three kinds of laser desensitization and immediate closure effect : the diameter and density of tubules in all laser groups were smaller than those in group A(P<0.05),and the closure rate of tubules in all laser groups was higher than that in group A(P<0.05).Pairwise comparison between laser groups : the average diameter and density of tubules in group C were higher than those in group B and group D,and the closure rate of tubules in group C was lower than that in group B and group D(P<0.05).Compared with group B and group D,the density of tubules in group D was lower than that in group B,and the closure rate was higher than that in group B(P<0.05),while there was no significant difference in the average diameter of tubules between group B and group D(P>0.05).(2)Comparison of long-term sealing effect of three kinds of laser desensitization : The average diameter and density of dentinal tubules in each laser group were significantly lower than those in group A after 3 months of wear,and the sealing rate of dentinal tubules was significantly higher than that in group A(P<0.05).Average diameter: Compared with each laser group,the average diameter showed an increasing trend with the increase of time.The diameter of tubules in C1 and C3 groups was larger than that in other laser groups at the same time point(P<0.05).There was no significant difference in the average diameter of tubules between Er:YAG laser and Er,Cr:YSGG laser at all time points(P>0.05).Density: The density of each laser group showed an increasing trend with the increase of time.At each time point,the tubular density of the laser group was Er,Cr:YSGG laser group <Er:YAG laser < Nd:YAG laser,and the difference between the two groups was statistically significant(P<0.05).Closure rate : The closure rate of each laser group decreased with the increase of time.The tube closure rate of Nd:YAG laser group was lower than that of Er:YAG and Er,Cr:YSGG laser groups at each time point(P<0.05).The closure rate of group D3 was higher than that of group B3(P<0.05).(3)Comparison of Ca/P ratio of dentin surface immediately after three kinds of laser desensitization: The Ca/P ratio of group B,C and D was lower than that of group A,and the Ca/P ratio of group C and D was significantly lower than that of group A(P<0.05).(4)Comparison of dentin surface hardness immediately after three kinds of laser desensitization: The hardness values of the three laser groups were slightly lower than those of group A,and there was no difference in Vickers hardness between the groups(P>0.05).Conclusion:(1)Er:YAG laser,Nd:YAG laser and Er,Cr:YSGG laser have a certain effect on the sealing of dentin tubules at the immediate and long-term desensitization.The best immediate and long-term sealing effect is Er,Cr:YSGG laser,followed by Er:YAG laser and Nd:YAG laser.(2)Nd:YAG laser and Er,Cr:YSGG laser desensitization treatment reduced the Ca/P ratio of dentin surface.(3)Er:YAG laser,Nd:YAG laser,Er,Cr:YSGG laser desensitization treatment had no effect on dentin surface hardness. |
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