| ObjectivesThe purpose of this paper was to evaluate the effect of Er,Cr:YSGG laser irradiation on the mechanical properties such as the compressive strength,the elastic modulus and the maximum strain of the dentin in root canal cleaning,while detecting the morphology of the teeth surface and the changes of teeth composition,so as to guide clinical applications.MethodA total of 60 extracted premolars were selected from female orthodontic patients aged 14 to 18 treated in the Department of Stomatology of Tianjin Medical University General Hospital from April to September 2015.Under the flowing water,using dental grinding machine along the CEJ boundaries,perpendicular to the long axis of teeth to remove the crown and root 1/3 parts of the teeth.Then along the long axis of the teeth from the central to crown of the root,we cut the teeth into the size of 1mm×2mm×6mm,making one dentin sample out of each prepared tooth.Afterwards,all sides of each dentin sample were polished with 10000 alumina water proof sandpaper,dried,measured with a flat thickness gauge and vernier caliper,and made into standard cuboid samples.Under the observation of microscope,40 smooth samples without cracks on surface were selected and randomly divided into 4 groups,each group made of 10 samples.Group A was set as the control group,Groups B,C,D as the experimental groups.Group A was not treated,while Groups B,C,D were treated with 1W,2W and 3W water laser respectively(time 30 s,distance 1mm).Using SEM to observe the morphology of the teeth surface and detecting the changes of the teeth composition by EDS,then using the universal testing machine to detect the elastic modulus,compressive strength and maximum strain of each sample,while describing the stress-strain curve of each group.In the process of the study,software SPSS 19.0 was used for the data analysis;the measurement data was described by mean plus or minus standard deviation;LSD-t test was used to compare among each two groups,multiple comparisons with the method of variance analysis,all statistical tests were two-sided;P<0.05 was considered a difference of statistical significance.Result1.The SEM results demonstrated that the surface of the dentin samples of each group after laser treatment was cleared,the opening tubule of the dentin presented a “cuff” appearance and there was no melting and cracking of the dentin.2.The results of EDS showed that Er,Cr:YSGG laser could increase the contents of Ca and P in dentin.3.The maximum compressive strength of Group A was significantly higher than that of Groups B,C,D(P<0.05)with different output energy,while there was no significant difference between the groups of B,C and D(P>0.05).4.There was no significant difference of the elastic modulus between Group A and B,nonetheless there was significant difference between Groups B,C and D(P<0.05),while the elastic modulus of Group B was significantly lower than that of Group C,the elastic modulus of Group C was significantly lower than that of Group D(P<0.05).5.The maximum strain of Group A was significantly higher than that of Group B(P<0.05),the maximum strain of Group B was significantly higher than that of Group C(P<0.05),meanwhile,the maximum strain of Group C was significantly higher than that of Group D(P<0.05).Conclusion1.Er,Cr:YSGG laser in root cleaning and disinfection can remove smear layer,open dentinal tubules,increase the calcium and phosphorus content of dentin surface.2.Er,Cr:YSGG laser can affect the maximum pressure,the elastic modulus and the maximum strain of dentin while in root cleaning and disinfection.3.Water laser with 1W energy cause less damage to dentin than 2W and 3W output laser. |
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