| Purpose The effect of Er:YAG laser on the bonding strength of dentin and general adhesive was evaluated by testing the bonding strength of Er:YAG laser pretreated dentin and observing the characteristic changes of the bonding interface,and the bonding mechanism was explored to provide a reference for clinical practice.Material and methods 132 complete human third molars were selected,of which 96 were used for bonding strength test and the remaining 36 were used for bonding interface observation.The samples used for bonding strength testing were randomly divided into two groups: immediate group and thermal cycles group.Each group was randomly divided into four subgroups according to the surface pretreatment method and the usage mode of general adhesive(group A: control + self-etching;Group B: control +acid etching(35% phosphoric acid);Group C: Er:YAG laser + self-etching;Group D:Er:YAG laser + acid etching).Each group of teeth was bonded with resin after corresponding pretreatment.The immediate group was stored in 37℃ normal saline for24 h for microshear strength test.The thermal cycles group was subjected to microshear strength test after 10,000 thermal cycles.The samples used for observation of the bonding interface were divided into four groups: A,B,C and D.The nine teeth in each group were divided into three groups according to the purpose of observation.3mm thick dentin discs and 2mm thick vertical section samples of the resin-dentin bonding interface and translucent grinding plates of the resin-dentin bonding interface containing rhodanine B were prepared respectively.The surface morphology of the pretreated dentin and the mass fraction of calcium(Ca)and phosphorus(P)were analyzed by scanning electron microscopy(SEM)and X-ray energy spectrometry(EDS).The interface characteristics of the pretreated dentin were observed by scanning electron microscopy(SEM)and confocal laser scanning microscope(CLSM).The data obtained were statistically analyzed by SPSS 26.0 software,and the data of each group were expressed as(mean standard deviation).Immediate shear strength was analyzed by one-way ANOVA,and multiple comparisons were made by LSD method.T-test is used to compare the shear strength between groups before and after cyclic aging.The P <0.05 is considered as a significant difference.Results The results of statistical analysis showed that the shear strength of Group B was the highest(21.95±3.5)MPa,and that of Group C was the lowest(15.36± 4.46)MPa.The difference of shear strength between Group B and Group A,C and D was statistically significant(P<0.05),there was no statistically significant difference in shear strength among groups A,C and D(P <0.05).After 10000 cycles,the bonding strength of group A,B,C and D is(18.07± 6.91)MPa(19.11 ±5.69)MPa(15.84±4.58)MPa and(16.16± 2.78)MPa,respectively.The immediate shear strength of group B and D is decreased,but there is no statistical significance between the four groups and their immediate microshear strength(P >0.05),and there was no significant difference in shear strength among the four groups(P >0.05.The results of interface characteristic analysis showed that the surface morphology of dentin was changed by Er:YAG laser pretreatment.Compared with the control group,the mass fraction of Ca was increased.In group C,there was A high density hybrid layer at the bonding interface,and the length and number of resin taps in groups B and C were significantly increased.Conclusion1.Compared with conventional etch-and-rinse strategie,the immediate bonding strength between dentin and universal adhesive was reduced by Er:YAG laser pretreatment,but there was no significant difference to the self-etch strategie.2.In both etch-and-rinse and self-etch strategies,Er:YAG laser pretreatment had no significant effect on the bonding stability of Single Bond Universal adhesive to dentin.3.The Er:YAG laser pretreatment changed the physical and chemical properties of the dentin surface,and formed a special high-density hybrid layer between the universal adhesive and the dentin. |
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