Effect Of Er:yag Laser Irradiation On Conventional Dentin Bonding

Objective: With the development of science and technology,the laser has been applied to treat the dental pulp.After the laser irrigation on tooth structure,how to get the best bonding results between the dental restoration materials and the dental organization is still unknow.In this study,the effect of Er:YAG laser irradiation on conventional dentin bonding were evaluated.Method: Sixty-six third molars with root development complete,no restoration,no fracture were selected.Thirty-three teeth without caries were randomly divided into A,B and C groups.And thirty-three teeth with caries were randomly divided into D,E and F groups.Each group had 11 teeth. The dentin surface of each tooth was treated with the Er:YAG laser(20Hz,20j/cm2,energy of the spot diameter is 2mm)irradiation with distilled water.Group A and D were bonded without etching;Group B and E were bonded with etching 15 seconds by 38% phosphoric acid;Group C and F were treated with the Er:YAG laser(20Hz,20j/cm2,energy of the spot diameter is 2mm) with distilled water.3M,Single bond2 was used as resin adhesive.In the first experiment, two teeth of each group Using scanning electron microscopy (Scanning Electron Microscopy SEM) observation of etched dentin surface after treatment the micro-morphology.In the second experiment, five teeth of each group were made into 0.1-0.5mm sheet in longitudinal slitting after light cured composite resin (3M , P60) repairing and stained with Rhodamine B fluorescent.Bonding interface morphology was observed using confocal laser scanning microscope(CLSM) after staining.The average thickness of mixed layer and the average length of resin-tag were calculated using software of CLSM.Statistical analysis was conducted for the final results.In the third experiment,five teeth of each group were illumination to cylindrical(diameter 3.1mm,high 4mm) . Mechanical properties of bonding interface (mixed layer) and shear bond strength were detected using shear test.And the statistical analysis was conducted.Result: In two types of dentin bonding treated with Er: YAG laser irradiation,the average thickness of mixed layer was no significant difference(P>0.05).The average length of resin tag was significant difference (P<0.05).The shear strength of mixed layer in ND was significant larger than CAD (P<0.05).In the same types of dentin bonding treated with Er:YAG laser irradiation,the average thickness of mixed layer was no significant difference(P>0.05).The average length of resin tag was significant difference (P<0.05).The shear strength of mixed layer in group B and E were larger than group C(P<0.05),and group F was larger than group A and D (P<0.05).Conclusion:1. Er:YAG laser irradiation did not affect the mixed layer thickness in different types of dentin treated with different approach.2. Treated with Er:YAG laser irradiation in the same method,the penetration of the binder in CAD was poorer than ND,and the shear bond strength of bonding interface was also smaller.3. Treated with Er:YAG laser irradiation in the same type of dentin,the penetration of the binder and the shear bond strength of bonding interface in 38% phosphoric acid etching group were the best,in Er:YAG laser-etch adhesive group were followed,and in direct bonding group were the worst.