| Objective:To study the adhesive strength of enamel and composite resin immediately after Er:YAG laser and/or Nd:YAG laser assisted bleaching of teeth,in order to provide guidance and experience for aesthetic restoration of anterior teeth.Methods:Experiment 1: Prepare 21 dental enamel slices,7 of which were divided into three groups.Seven were treated as follows: Group A(non bleaching group),Group B(conventional bleaching group),Group C(Er:YAG laser group),Group D(Nd:YAG laser group),Group E(first Er:YAG laser followed by Nd:YAG laser group),Group F(first Nd:YAG laser followed by Er:YAG laser group),and Group G(Beyond cold light group).Scanning electron microscopy was used to observe three treatment stages,one was to observe the enamel surface after bleaching,the other was to observe the use of 35%phosphoric acid etching on the enamel surface after bleaching,and the third was to observe the completion of the bonding between the enamel surface and the composite resin after using 35% phosphoric acid etching after bleaching.The vertical bonding interface was cut through the specimen,and the ultrastructure of the bonding interface between the enamel and the composite resin was observed.Experiment 2: 70 adhesive specimens were prepared and randomly divided into 7 groups(n=10)according to different bleaching methods.After the above treatment,the adhesive strength between enamel and composite resin was tested.After the shear test,the specimens were subjected to a microscope × Observe the fracture mode of each group of specimens at a magnification of 20,and randomly select one specimen from each group to observe the ultra-fine surface structure of the debonding using a scanning electron microscope.Result:Experiment 1:After bleaching treatment,the enamel surface of group A was smooth and no abnormalities were observed;The surfaces of Group B and Group G are slightly rough,with visible scratches in some areas;The enamel surface of groups C,D,E,and F was rough and had morphological changes.After acid etching and bleaching treatment,the surface of enamel in groups A,B,and G was similar,with honeycomb like surfaces and localized fracture layers in some areas;After acid etching,the surface morphology of groups C,D,E,and F was uniform,and no large pits or fracture zones were observed.The bonding interface between enamel and composite resin:Group A showed a tight bonding interface between enamel and composite resin;Group B and Group G showed a fracture zone at the bonding interface between enamel and composite resin,with only adhesive residue on the surface;Groups C,D,E,and F showed tight bonding between enamel and resin protrusions,with uniform and regular resin protrusion infiltration.Experiment 2:The shear strength of enamel and composite resin between the seven treatment groups was statistically significant(P<0.05).The intra group comparison showed that the shear strength of Group A was significantly different from that of Group B,Group C,Group D,Group E,Group F and Group G(P<0.05);The shear strength of group B was significantly different from other groups A,C,D,E,F(P<0.05);There was no significant difference between Group B and Group G(P>0.05).The results of shear strength between Group C,Group D,Group E and Group F showed no significant difference(P>0.05).The fracture mode results showed that in the test group,the main fracture mode of the bonding interface between Group B and Group G was adhesive and resin layer fracture,while the other groups were mixed fractures of adhesive resin layer and resin layer fracture.No enamel layer fracture was observed in all groups.Ultrastructure of debonding:Group A showed a large amount of resin and adhesive residue on the surface of enamel due to debonding;The debonding surfaces of Group B and Group G showed that only adhesive residue was present on the enamel surface,with less resin;Groups C,D,E,and F showed a mixture of resin and adhesive residues on the enamel surface.Conclusion:1.Er:YAG laser and Nd:YAG laser activated bleaching can improve the immediate bonding strength between enamel and composite resin2.Er:YAG laser and Nd:YAG laser-assisted bleaching is superior to cold light bleaching in recovering immediate adhesive strength3.Er:YAG laser and Nd:YAG laser assisted bleaching have no obvious advantages over laser assisted bleaching in restoring adhesive strength... |
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