The Influence Of Er:YAG Laser Irradiation On Rebonded Shear Bond Strength Of Enamel

[Objective]This study aims to evaluate the Er:YAG laser irradiation influence on enamel re-adhesion properties by:1.Comparing efficiency of adhesive removal done by different treatments on the enamel surface through the comparison of morphology of the enamel surface,2.Comparing rebonding strength of enamel and resin in each group by the shear bond strength test.[Methods]80 pieces of premolars and third molars that were without any caries, fillings or fold crack were collected. After pre-treatment of embedding, grinding, polishing and building up failure model,120 failed enamel bond specimens were made.The specimens were subsequently randomly divided into 7 groups based on different surface treatments:Group A was as control(n=16). Group B was treatment by conventionally grinding (n=14). Group C was retreated surface by sandblasting (n=14). Group D (frequency=5Hz, n=24), group E (frequency=10Hz, n=24), group F (frequency=15Hz, n=24), group G (frequency=3Hz, n=4), these 4 groups were irradiated under laser radiation which was set to 275mJ/pulse, and laser beam spot diameter of 1mm.2 specimens from each group were observed to compare the morphology of the enamel surface and section after these treatments and to evaluate the influence of Er: YAG laser on adhesive removal and enamel losses by scanning electronic microscope (SEM).4 specimens from group A (two of which would be etched by etching agent) and 2 specimens from other groups were observed to observe the enamel surface and quantified the fluorescent adhesive through Caliper IVIS Spectrum System and to evaluate the efficiency of adhesive of each groups.The remaining 90 specimens were maintained at 37% distilled water for 48 hours. Then specimens from group D, E, F were separated into two groups randomly and respectively, referred as group D1, D2, E1, E2, F1, F2. Etch the enamel surface of specimens from group A, B, C, D1, El, F1 by 35% phosphoric acid, while the ones from group D2, E2, F2 were not. Specimens were then rebounded with resin in the restricted area (the adhesive was 3M Single Bond 2; and we used 3M Valux Plus resin; light curing 40s by LED light). All the specimens were then put at room temperature for half an hour and then stored in 4℃ distilled water for 24 hours. After all the rebonding process, the specimens were embedding in the PVC tube, and the shear bond strengths were tested by the universal testing machine.Statistical analysis was performed using SPSS 22 statistics system. Data of the shear rebond strength of different groups were separately analyzed by one way analysis of variance (ANOVA) and SNK tests for pairwise comparisons among groups (p<0.05). The data of shear rebond strength of different groups (group D1, D2, E1, E2, F1 and F2) were separately analyzed by two-way ANOVA analysis and SNK tests for pairwise comparisons among groups (p<0.05).[Results]1. Depending on observation of the Scanning Electron Microscope, Er:YAG laser irradiation on the enamel surface could not achieve the goal of selective removal of remained adhesive on enamel. While there was certainly enamel loss during the laser irradiated process.2. Fluorescence observation by Caliper IVIS Spectrum System showed that the efficiency of adhesive removal by different frequencies Er:YAG laser radiation was variant, and the law still needed further exploration.3. Re-bond strength of each group:Control+etching (group A):14.08 ± 1.67MPa; grinding+etching (group B):21.02 ± 1.73MPa; sandblasting+etching (group C): 14.41±1.36MPa; 5Hz Er laser+etching (group D1):21.45 ± 1.38MPa; 5Hz Er laser (group D2):19.21 ± 1.12; 10Hz Er laser+etching (group E1):17.69 ± 1.86MPa; 10Hz Er laser (group E2):15.40 ± 1.99MPa; 15Hz Er laser+etching (group F1): 16.79 ± 1.93MPa; 15Hz Er laser (group F2):16.32 ± 1.26.4. According to data analysis by SPSS, the differences among the experimental groups were significant (p<0.05). Group B and group D1 presented the highest bond strength value. There were no significant differences(p> 0.05) between group B and group D1, while there were significant differences (p<0.05) among these 2 groups with other 7 groups. Group D2 presented different significantly from other 8 groups. There were no significant differences(p> 0.05) among group Fl, group E1 and group F2. There were no significant differences(p> 0.05) among group E1, group F2 and group E2. The group A and group C presented the lowest bond strength value.5. In the comparison of laser irradiated groups, the rebond strength of enamel was increased by retreatment of etching, and there were significant differences (p<0.05) between etching and no-etching.5Hz laser irradiation presented the highest rebond strength value. There were no significant differences (p> 0.05) between the 10Hz and 15Hz laser irradiation.[Conclusions]1.Compared with the control group, there were definite effects in the adhesive removal by surface treatment process of each group. The efficiency of adhesive removal by grinding is the highest, and the influence on different frequencies of Er: YAG laser radiation was variant.2. Er:YAG laser irradiation on the enamel surface could not be selective removal of remaining adhesive on enamel, while there was certainly enamel loss during the laser irradiated process.3. The rebond strength of enamel can be increased by Er:YAG irradiation on enamel surface. Combination with etching, it could be preferable.4. Influence on rebond strength of different Er:YAG laser radiation was variant. When it went 275mJ/pulse, frequency of 5Hz Er:YAG irradiation presented the highest rebond strength value, which was similar to the grinding group.5. Er:YAG laser on enamel rebonded process could achieve similarcurative effect of the conventional grinding process, and with such advantages as safety, efficiency, and comfort, we can choose laser therapy rather than grinding in clinical cases.