| Objective:Feldspathic ceramic has been widely used in all-ceramic restoration for its advantages, such as natural beauty and good biocompatibility. However, easy to loose off is always a tough problem in clinic. Using hydrofluoric acid for surface pretreatment of feldspathic ceramic can increase bonding strength between feldspathic ceramic and teeth, and has been widely recognized and applied, whereas its corrosiveness and toxicity are still potentially harmful to human body.To investigate the feasibility for using Er:YAG laser for pretreating the surface of feldspathic ceramic, evaluate the effect of bonding strength and marginal adaptation between feldspathic ceramic and dentin, and provide experimental basis for clinical research on ceramic surface treatment without acid etching.Methods:1 Micro-morphology observation of the surface of feldspathic ceramic pretreated with different powers of Er:YAG laser1.1 Sample preparation and groupingCEREC Blocs were cut into pieces as size of 6 mm×6 mm×2 mm, and polished with 1000# sandpaper. Thirty pieces without superficial or internal defects observed by stereomicroscope (×10) were included in this study.Ceramic pieces were randomly divided into 5 groups (6 for each group): Group A (control group, no treatment to surface of ceramic pieces); Group B (surface of ceramic pieces pretreated with 9.6% hydrofluoric acid for 40 seconds); Group C (surface of ceramic pieces treated with Er:YAG laser at 300 mJ,15 Hz); Group D (surface of ceramic pieces pretreated with Er:YAG laser at 400 mJ,15 Hz); Group E (surface of ceramic pieces pretreated with Er: YAG laser at 500 mJ,15 Hz). Group C-E were pretreated by the same Er: YAG laser machine (Israel, Syneron LiteTouch), with 14# working tip,1 mm and 70°～90° inclined angle to the surface of ceramic pieces, radiating 10 seconds by reticulated scanning. All procedures was finished by the same operator who was uniformly trained.1.2 Scanning electron microscope observationAfter the surface treatment of each group, all samples were put into a 37 ℃ thermostat for drying and sprayed gold onto the surface. The surface morphology of samples in each group was observed by Scanning Electron Microscope. Select the parameter which got the best etching effect as the Er: YAG laser working energy used in following experiments.2 Microleakage observation of the effect of Er:YAG laser preteatment on bonding property between feldspathic ceramic and dentin2.1 Sample preparationCEREC Blocs were cut into pieces as size of 6 mm×6 mm×2 mm, and polished with 1000# sandpaper. Thirty pieces without superficial or internal defects observed by stereomicroscope (×10) were included in this study.Thirty third molars with no caries or defect extracted for impaction or periodontal disease were collected from the department of oral surgery, Stomatological Hospital of Hebei Medical University from June 2015 to December 2015. Cut the crown perpendicular to tooth axis into 30 dentin pieces as size of 6 mm×6 mmx2 mm, and polished them with 1000# sandpaper. Choose 30 pieces without superficial or internal defects by stereomicroscope (×10).2.2 GroupingAccording to the different surface treatment, ceramic pieces were randomly divided into 3 groups (10 for each group):Control group:surface of ceramic pieces treated with silane coupling agent; Laser group:surface of ceramic pieces treated with Er:YAG laser (500 mJ,15 Hz) and silane coupling agent; Acid group:surface of ceramic pieces treated with 9.6% hydrofluoric acid and silane coupling agent.All dentin pieces were divided into 3 groups randomly, and 10 for each. Adhesive surface of dentin pieces were treated with etching agent of ParaCore system.2.3 Microleakage observationAll groups of ceramic pieces and dentin pieces were bonded by the same adhesive system (Switzerland Coltene, ParaCore), cured by the same curing light for 20 seconds from each side. Thermocycling experiment was conducted by the same thermocycler (Suzhou, TC-501F) after 24 hours. Three bonding interfaces of ceramic-dentin blocs were embedded in self-curing resin for bonding specimen preparation. All the bonding specimens were immersed in 2% methylene blue solution. Microleakage was observed by stereomicroscope (×10, ×25) and dye penetration depth was measured. 2.4 Statistical analysisThe statistical analysis was performed with SPSS 16.0. The arithmetic mean and standard deviation were calculated for statistical description of the data. One-way ANOVA was performed to evaluate the measurement results of dye penetration depth between ceramic pieces with different surface treatment bonding to dentin pieces; SNK-q test was performed to compare within the three groups. Statistical significance was established at P<0.05.3 The effect of Er:YAG laser pretreatment on bonding strength between feldspathic ceramic and dentin3.1 Sample preparation and groupingIn accordance with the standards in part two, ceramic and dentin samples were prepared and selected.3.2 Bonding specimen preparationAll the dentin pieces were embedded in self-curing resin, leaving adhesive surface sticking to a double-sided adhesive with a hole of 6 mm in diameter for limiting adhesive area. Keep the adhesive surface clean. All groups of ceramic pieces and dentin pieces were bonded by the same adhesive system and cured by the same curing light. Thermocycling experiment was conducted by the same thermocycler 24 hours after bonding specimens prepared.3.3 Bonding strength testAfter thermocycling experiment, shearing strength test was carried out using the same universal testing machine (Shenzhen, CMT6104) with a cross-head speed of 1 mm/minute, at room temperature of (20±2)℃. Bond failure mode was observed by stereomicroscope (×10).Shearing strength=Maximum load value when bonding specimen was destroyed/adhesive area3.4 Statistical analysisThe statistical analysis was performed with SPSS 16.0. The arithmetic mean and standard deviation were calculated for statistical description of measurement data. Kruskal-Wallis test was performed to evaluate the effect of shearing strength between ceramic pieces with different surface treatment bonding to dentin pieces; R×C Chi-square test was performed to compare bond failure mode among the three groups. Statistical significance was established at P<0.05.Results:1 Micro-morphology observation of the surface of feldspathic ceramic pretreated with different powers of Er:YAG laserThe results of SEM analysis showed that in Group A, relatively regular crystal structure can be found on the surface of ceramic pieces. In Group B, different sizes of micropore-like structure can be found on the surface of ceramic pieces after treated with 9.6% hydrofluoric acid, some of pores fused together to form large ones. Surface of ceramic pieces could be roughened by Er:YAG laser with different powers. In Group C and D, pit-like structures, which were shallow and irregular, can be found on the surface of ceramic pieces after treated by Er:YAG laser at 300 mJ,15 Hz and 400 mJ,15 Hz, while structure in Group E were relatively deeper and more regular.2 Microleakage observation of the effect of Er:YAG laser preteatment on bonding property between feldspathic ceramic and dentinDifferences in dye penetration depth among three groups were statistically significant (F=40.856, P=6.80×10-9). The dye penetration depth in Laser group and Acid group were both lower than that in Control group, but there was no difference between Laser group and Acid group.3 Study on the effect of Er:YAG laser pretreatment on bonding strength between feldspathic ceramic and dentinDifferences in shearing strength among three groups were statistically significant (x2=20.720, P=3.17×10-5). The shearing strength in Laser group and Acid group were both higher than that in Control group, but there was no difference between Laser group and Acid group. Differences in bond failure mode among three groups were statistically significant (χ2=13.908,P=0.031). The bond failure mode in Laser group and Acid group were both significantly different from that in Control group, but there was no difference between Laser group and Acid group.Conclusions:1 Er:YAG laser with different powers pretreatment can roughen the surface of feldspathic ceramic. The effect of Er:YAG laser at 500 mJ,15 Hz is superior to that of Er:YAG laser at 300 mJ and 400 mJ.2 Pretreating the surface of feldspathic ceramic by using Er:YAG laser at 500 mJ,15 Hz or 9.6% hydrofluoric acid can both improve the marginal adaptation and decrease microleakage between feldspathic ceramic and dentin. There was no significant difference between such two methods.3 Pretreating the surface of feldspathic ceramic by using Er:YAG laser at 500 mJ,15 Hz or 9.6% hydrofluoric acid can both improve the bonding strength between feldspathic ceramic and dentin. There was no significant difference between such two methods. |
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