Dentin Bond Strength: Influence Of Ultra-short Pulse Er: YAG Laser

Objective To apply Er: YAG laser in the treatment of oral diseases with its advantages of hard tissue cutting,painless,high efficiency and low noise.It was found that the dentin surface treated by Er: YAG laser was observed by electron microscope.The dentin tubules were open,and the dentin surface had no stain layer and was uneven,which increased the bonding area.In this study,the bonding strength of dentin treated by ultra-short pulse Er: YAG laser was investigated,which provided experimental basis for clinical application and had good application and development value of oral therapy technology.Methods 144 isolated healthy third molars were selected,and the neck of the teeth was cut at 60° with the long axis of the tooth body using high-speed turbine.The crown of the teeth was taken as the test specimen.The treatment sequence of the tooth surface was polished step by step with water sandpaper to 600 mesh to make the dentin bond surface smooth and smooth.The specimens were placed in an ultrasonic oscillator with a temperature of 20℃ for 60 min for continuous shock.The specimens were taken out and stored in normal saline for later use.128 specimens used for bonding strength test were embedded in a PTFE mold to expose the dentin bonding surface.128 resin columns are prepared with a mould with diameter of 2mm and height of 4mm.The 16 specimens for observation were made into dental pieces with thickness of 0.5mm,length of 5mm and width of 5mm.The dentin surface morphology was observed after dehydration and fixation.The strength test specimens were randomly divided into two groups: conventional test group and hot and cold cycle group.Each group was randomly divided into eight subgroups according to different surface pretreatment methods and binder use patterns.G1 group: blank control group,G2-G5 group,30 MJ,20Hz Er: YAG laser treatment,pulse width of 30 us,40us,50 us,60us,respectively;G6group: total acid etching group;Group G7:30MJ,20 Hz,40us pulse width Er: YAG laser+ acid etching,Group G8:30MJ,20 Hz,40us pulse width Er: YAG laser.Surface treatment was performed according to the requirements of the groups,128 specimens were bonded to the resin column by different bonding systems.The hot and cold cycle groups were respectively circulated for 5000 times in the water tank set at 5℃ and 55℃,and then used together with the conventional bond group to test the shear bond strength by universal mechanical testing machine(UTM),and the fracture surface morphology was observed by stereophil microscope.Scanning electron microscope(SEM)was used to observe the surface morphology of bonding surface after different treatments.One-way analysis of variance was used for the conventional bond group and the hot and cold cycle group;SNK test was used for pound-for-pair comparison in the intergroup analysis;independent sample T test was used for data difference between the two subgroups,and P<0.05 was statistically significant.Results Experiment 1: To explore the optimal pulse width of ultra-short pulse Er: YAG laser to improve the dentine bonding strength.Experiment 2: To explore the influence of different bonding systems and Er: YAG laser on dentine bonding strength.In experiment 1,G1-G5 group,SEM showed that after different pulse width Er: YAG laser treatment,the dentin surface was irregular,the stain layer was removed,and the dentin tubules showed different degrees of opening.In group G1,the dentin surface was flat with scratches left after polishing,and the dentin tubules were closed by particles in the stained layer.In G2 group,the dentin tubules were semi-open and cuff-like.In G3 group,the dentin tubules were completely open,the peritubular dentin was prominent,and the boundary between it and the surrounding area was clear.The cuff shape was more obvious,and there were microcracks.The collagen fibers on the surface of group G4 collapsed and slightly melted.The dentin tubules were partially covered,and the morphology was not obvious.The boundary between group G4 and the surrounding area was not clear,and there were slight cracks.After G5 treatment,the collagen fibers on the dentin surface collapsed,there was a large area of melting,obvious cracks,and almost all dentin tubules were covered.In the conventional bonding group,the maximum value of SBS was in G3 group(14.53±2.83Mpa),the minimum value was in G1 group(3.46±1.08Mpa),and the mean value was G3>G2>G4>G5>G1.There were statistical differences among G1 group,G2 group,G3 group,G4 group and G5 group(P<0.05).The differences between G2 group and G4 group,G5 group and G1 group were statistically significant(P<0.05).There were significant differences among G3 group,G4 group,G5 group and G1 group(P<0.05).There were significant differences between G4 group and G1 group,G2 group and G3 group(P<0.05).There was statistical significance between G5 group and G1 group,G2 group and G3 group(P<0.05)..After the cold-heat cycle experiment,the maximum value of SBS was in G3group(9.04±2.42Mpa),the minimum value was in G1 group(2.05±1.38Mpa),and the mean value was G3>G4>G2>G5>G1.There was no statistical significance in the mean value difference among G7 group,G8 group and G3 group,while there was statistical significance between G6 group and G7 group,G8 group and G3 group(P<0.05).There were statistically significant differences between the conventional bond group and the cold-heat cycle group(P<0.05).The fracture patterns under the microscope were divided into three types,type 1: bond failure;Type 2: Cohesion failure;Type 3: mixing failure.The fracture patterns of each group are mainly type 1 and type 3.Conclusion1.30 MJ,20Hz Er: YAG laser(2.94um)pulse width of 40 us can significantly improve the bonding strength of dentin.2.30 MJ,20Hz,40 us pulse width Er: YAG laser combined with self-etching and total etching treatment,there is no difference in bond strength3.When Er: YAG laser(3.30 MJ,20Hz,pulse width 40us)was combined with total acid etching,the acid etching sequence had no effect on the bond strength.4.The bonding strength of 4.30 MJ,20Hz,40 us pulse width Er: YAG laser combined with acid etching was better than that of only acid etching.5.In clinical work,it is suggested to treat dentin with Er: YAG laser of 30 MJ,20Hz and40 us pulse width combined with self-acid etching.