Effect Of Er:YAG Laser At Different Output Powers On Bond Strength Of Non-carious Sclerotic Dentin

Background and ObjectiveTooth wear has complex and multi-factorial etiologies that result in the surface continuous loss of dental hard tissue,including erosion,attrition,abrasion,and abfraction.It is more common in adults and the incidence tends to increase with age.Tooth wear has become a new oral health problem.Resin composite restoration is often used in the treatment of tooth wear.However,the restoration shows the poor bond effect.When continuous tooth wear reaches the dentin,there is an increased peritubular dentin apposition and deposition of mineral in the dentinal tubules,and the dentin becomes sclerotic.Studies have showed that the bond strength of sclerotic dentin is lower than that of sound teeth.many researchers have tried to find ways to improve the bond strength of non-carious sclerotic dentine,such as pretreatment with diamond bur polishing,acid etching,EDTA pretreatment,laser irradiation,etc.However,the effectiveness of these approaches has been insufficient for clinical application.In recent years,the Er:YAG laser(erbium yttrium aluminum garnet)are widely used in treating tooth hard tissue because it is minimally invasive,comfortable and accurate.The effects of Er:YAG laser on bond strength of tooth hard tissue is controversial.There has been a lack of studies investigating the influence of Er:YAG laser treatment on bonding to non-carious sclerotic dentin and whether the power of Er:YAG used in clinical is optimal to non-carious sclerotic dentin,so these questions should be further researched.The aim of this study is to evaluate the influence of Er:YAG laser treatment at different output powers on the bond strength of non-carious sclerotic dentin and then to determine the optimal power of the Er:YAG laser for clinical application.Methods1.The effects of Er:YAG laser at different output powers on the surface morphology of non-carious sclerotic dentin.The fourteen teeth with typical sclerotic dentin on the occlusal surface were randomly divided into 7 groups according to various treatments(A:the control group,B:self-etching with Prime&Bond universal,C:diamond bur polishing followed by Prime&Bond universal,D-G:Er:YAG laser irradiating at 0.6W,0.8W,1.0W,1.2W output power,respectively,followed by Prime&Bond universal).The scanning electron microscope was used to observe the surface morphology of the sclerotic dentin.2.The effects of Er:YAG laser at different output powers on bond strength of non-carious sclerotic dentin.The Thirty teeth with typical sclerotic dentin on the occlusal surface were randomly divided into 6 groups according to various treatments(A:Self-etching with Prime&Bond universal,B:diamond bur polishing followed by Prime&Bond universal,C-F:Er:YAG laser irradiating at 0.6W,0.8W,1.0W,1.2W output power).After Restoring with resin composite,each tooth was sectioned into several sticks and 15 sticks of sclerotic bonding areas were selected(n=15 per group).micro-tensile bond strength test and bonding failure mode analysis was used to evaluate the bond strength.Results1.Group A:The surface of the sclerotic dentin was appeared to have a contamination laser and we could observe few open dentinal tubule.Most dentinal tubules were filled with sclerotic casts.Group B:we can see that after the use of the Prime&Bond universal,the superficial contamination layer disappeared.Partial demineralization occurred on the superficial layer of sclerotic dentin.Group C:In the diamond bur group,most dentinal tubules were covered with debris.only a few dentinal tubules remained partially exposed in SEM images.Group D-G:SEM observation showed that the surface morphology of the sclerotic dentin changed after Er:YAG laser pretreatment at different output power.The surface of the sclerotic dentin were rough without smear layer after Er:YAG laser irradiation with the increase of the output power of Er:YAG laser,more dentin tubules can be seen and the boundary between the peritubular dentin and intertubular dentin was more obvious.Parts of the peritubular dentin protruding out of the surface.The honeycomb-like change was found on the intertubular dentin.the dentin tubules were still small or completely blocked.cracks can be seen when the output power is 1.2W.2.Er:YAG laser pretreatment at different output powers have a significant effect on the micro-tensile bond strength of sclerotin dentin(P<0.05).The bond strength of the group A(Self-etching)was significantly lower than that of the other 5 groups(P<0.05).The micro-tensile bond strength of the group B(diamond bur)was not significantly different from that of the group C(0.6W)(P>0.05).The micro-tensile bond strength of the group B(diamond bur)and group C(0.6W)was significantly lower than that of the group D(0.8W),group E(1.0W),and group F(1.2W)(P<0.05),but there was no significant differences among the bond strength of the group D(0.8W),group E(1.0W)and group F(1.2W)(P>0.05).ConclusionsEr:YAG laser preparation at the power of 0.8W,1.0W and 1.2W can help to improve the micro-tensile bond strength of non-carious sclerotic dentin,but the optimal output power is not sure yet.As cracks can be seen on the surface of sclerotic dentin when the power is 1.2W.Considering both the effectiveness and safety of the Er:YAG laser,when dentists improve the micro-tensile bond strength of non-carious sclerotic dentin in clinic,the output power of 0.8W(80mJ,10Hz)is recommend according our experimental result.