| Objective:To explore the appropriate parameters of irradiation energy and the sealing effect on dentine tubules by Nd:YAG laser irradiation on dentin samples in vitro,so as to provide reference for clinical application.Methods:120 open samples of dentin tubules were prepared by incising 1 mm above and below the enamel-cementum boundary of complete premolars extracted from orthodontic teeth.40 samples were randomly selected and divided into four groups,10 in each group.The irradiation surfaces of all the dentin samples were fixed upward,and the laser head was fixed.The Irradiation Center was aligned with the center of the sample.The distance between the optical fiber and the dentin surface was 1 mm,and the area of the spot was about 0.9-1 mm2,30mJ/10Hz,50mJ/10Hz and 70mJ/10Hz,respectively Dentin samples were irradiated with 90mJ/10Hz power for 60 seconds.The changes of dentin surface structure were observed by SEM.A laser parameter which can effectively seal dentin tubules was selected for the following experimental study.For the following experimental studies.The remaining 80 samples of open dentin tubule model were randomly divided into 8 groups:group A?B?C?D?E?F?G?H?group A(blank control group):dentin samples were not treated;group B(fluorine varnish group):fluorine varnish was uniformly coated with fine brush on the working face of the sample;group C(laser group):laser irradiation of the sample with the appropriate parameters selected above,the same method;Group D(fluorine varnish+laser group):The samples were uniformly coated with fluorine varnish with a fine brush,and then irradiated by laser with the suitable parameters selected above.The changes of dentin surface structure,dentin melting depth/penetration depth,dentin tubule diameter and dentin tubule density were observed under SEM.Group E(blank+dye solution control group),Group F(fluorine varnish+dye solution group),Group G(laser+dye solution group),Group H(fluorine varnish+Laser+dye solution group),the corresponding treatment method was the same as group A?B?C?D,then stained with 2%methylene blue dye solution,and then slowly molten the dentin from the bottom of the sample until the dye penetration point was seen,using vernier caliper(accurate to 0.01mm)under the body microscope(30X).Measure the dye penetration depth of each sample.Results:1.Changes of dentin surface structure after laser irradiation with different energy parameters:SEM observation:30mJ/10Hz,50mJ/10Hz laser irradiation showed no change in dentin surface structure,no obvious closure of dentin tubule orifice and no obvious change in tubule diameter;90mJ/10Hz laser irradiation showed carbonization of dentin surface,pit-like changes in irradiation center,and nodules of surrounding dentin tubules.The 70mJ/10Hz laser irradiated dentin samples showed that the dentin tubules were sealed without obvious damage during melting,which could effectively seal most of the dentin tubules,which was the suitable laser irradiation parameter in this experiment.2.Sealing of dentine tubules in each group:Dentin surface structure:the orifice of dentine tubules in group A was completely open and the surface was normal;the surface of dentin in group B was covered with paste material and a little debris,and no exposure of dentine tubules was observed;most of dentine tubules in group C were sealed without obvious cracks;the orifice of dentine tubules in group D was covered with paste,and the dentine tubules were completely closed.The mean diameter of dentine tubules orifice was 2.78±0.38?m in group A,1.64±0.22?m in group C,and was lower than that in group A(p<0.05).The mean diameter of dentine tubule orifice in group B and group D was 0 micron due to complete closure of dentine tubules.Dentin tubules density:group A 24.89±0.58 10~3/mm~2,group C 7.53±0.70 10~3/mm~2,group C dentin tubule density was lower than group A(p<0.05);group B and group D dentin tubule density was 0 10~3/mm2 due to complete closure of dentin tubules.The melting/penetration depth of dentin tubules in group B was 4.5±0.59?m,26.44±2.82?m in group C and 10.17±1.20?m in group D.The melting/penetration depth in group A was 0?m due to untreated samples.The melting/penetration depth in group C was higher than that in group B.There was a statistical difference between the two groups(p<0.05).Dye penetration depth:group E 1.91±0.07 mm,group F 0.56±0.07 mm,group G 1.56±0.10 mm,group H 0.18±0.05 mm;group E,group G and group F dye penetration depth is higher than group H,there is a statistical difference between the two groups(p<0.05).Conclusion:1.Under the experimental conditions,most dentine tubules can be effectively sealed when Nd:YAG laser energy parameter is set to 70mJ/10Hz,distance between optical fiber and dentin surface is 1 mm,spot area is about 0.9-1 mm2 and irradiation time is 60 seconds.2.Nd:YAG laser irradiation can reduce the diameter of dentin tubule orifice and density of dentin tubule,increase the melting depth,and achieve the function of sealing dentin tubule.3.Nd:YAG laser can effectively promote the penetration of fluorine varnish and reduce the penetration depth of dye after fluorine varnish is coated.It can provide some references for the clinical application of Nd:YAG laser. |
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