Effect Of Er: YAG Laser Etching Dentin With Different Energy Densities On Bond Strength

Objective:This experiment using Erbium doped yttrium aluminum garnet laser（Erbium-dopd yttrium aluminum garnet,Er:YAG）different etching dentine surface,the energy density compared with conventional acid corrosion,through scanning electron microscopy（SEM）images,dentin-resin shear bond strength,dentine-resin fracture model,compare different energy density Er:YAG laser influence on dentine-resin bond strength,for laser etching dental tissues for clinical application in the fixed directly provide experimental basis.Methods:Eighty fresh caries-free third molars aged from 18 to 40 years were selected to remove the enamel and expose the middle dentin.Dentine plane specimens were prepared and randomly divided into 10 groups（n=8）.（C₀）blank control group,positive control group（C₁）,Er:YAG laser group（L₁,L₂,L₃ and L₄）,Er:YAG/acid corrosion joint group（LA₁,LA₂,LA₃,LA₄）,adjust the laser in non-contact mode,R14 handle,set up the laser parameters:the MSP mode,the frequency of 20 Hz,ratio soda（7:3）m L/min,spot diameter 1.3 mm,light speed of 1 mm/s,laser energy L₁,LA₁:40 m J;L₂,LA₂:60 m J;L₃,LA₃:80 m J;L₄,LA₄:100m J,after laser treatment LA₁,LA₂,LA₃,LA₄ and then 37%phosphoric acid treated..In each group,2 cases were observed by scanning electron microscopy（SEM）.The remaining 6 cases in each group were bonded with X-Trafill composite resin by 3M Single Bond 2,respectively.A total of 60 dental resin blocks（n=6）with a cross-sectional area of 4.0 mm×4.0 mm and a length of about 8 mm were prepared for shear bonding strength test.The fracture types were observed by a volume microscope.All data were statistically analyzedResults:1.Scanning electron microscope images:in the blank control group,the stain layer on the dentin surface was obvious,and the dentin tubules were not visible;In the positive control group,the dentin showed honeycomb changes with clean surface and uniform shape.The dentin tubule orioles were clearly exposed with a small amount of stain layer.In the Er:YAG laser group,the dentin tubule orifice was irregular"crater"like depression,and cracks appeared with the increase of laser energy,and the diameter of dentin tubule was different.In Er:YAG/acid etched combination group,dentin was similar to the change of dentin after acid etched,but with the increase of energy density,the diameter of dentin tubule was different.2.The dentin-resin shear strength test:the shear strength of blank control group（C₀）,positive control group（C₁）,Er:YAG laser group（L₁,L₂,L₃ and L₄）,Er:YAG/acid etched combined group（LA₁,LA₂,LA₃,LA₄）were as follows:（13.52±0.66）MPa,（21.43±0.86）MPa,（23.00±1.46）MPa,（23.75±1.05）MPa,（23.36±1.20）MPa,（23.52±1.11）MPa,（25.30±0.63）MPa,（25.39±0.86）MPa,（25.29±0.96）MPa,（25.72±0.73）MPa,Single factor analysis of variance tip positive control group,the Er:YAG laser group,Er:YAG/acid corrosion joint group and blank control group the difference had statistical significance（P<0.05）,Er:YAG laser group,Er:YAG/acid corrosion joint group and positive control group the difference had statistical significance（P<0.05）,Er:YAG laser in the way two comparison difference has no statistical significance（P>0.05）,Er:YAG/acid corrosion within the united way comparing two differences have no statistical significance（P>0.05）.3.The fracture types were mainly mixed fracture types（73%）,dentin or composite resin damage（22%）,cohesive fracture types（5%）,and there was no significant difference between the two groups（P>0.05）,suggesting that the difference of fracture types was not related to laser etching alone or combined acid etching.Conclusion:1.The bonding strength of the dentin etched by Er:YAG laser alone is similar to that of traditional acid etching,and the bonding strength of Er:YAG laser can be obtained at 40m J 20Hz in MSP mode.2.Er:YAG laser etching combined with acid etching can achieve higher bonding strength than Er:YAG laser etching alone or acid etching alone.3.Based on the study of this experiment,when Er:YAG laser is used for dentin etching,the energy density is less than 60m J,which is a relatively safe parameter.