Effect Of Different Energy Density Of Nd:YAG Laser Irradiation On The Dentin Bond Strength & Clinical Case Report

Objective:to evaluate the Effect of different energy density of Nd:YAG laser irradiation on the dentin bond strength. And to explore the changes of mechanical and chemical properties of dentine surface after laser irradiation dentine bond strength changeExperiment ? The influence of Nd:YAG laser irradiation on the immediate dentin bond strength and nanoleakage of the bonding surfaceMethod:36 intact third molars were used. After the enamel of occlusal surfaces was removed, they were randomly divided into three groups. For the experimental groups, the dentin surfaces were treated with 1w,85J/cm? (high energy density group) or 4w, 350J/cm2 (low energy density group) Nd:YAG laser irradiation before adhesion step, specimens without any treatment served as control. Then each group was divided into two sub-groups in order to evaluate the bonding strength of both self-etching adhesive agent (G-Bond, GC) and etch and resin adhesive agent (Single Bond 2,3M ESPE). The dentin surfaces were observed by SEM and LSCM.Results:After irradiated by low energy density laser, etch and resin bonding strength was stable and self-etch bonding strength was decreased. In contrast, self-etch bonding strength was maintained and etch-and-rinse bonding strength was decreased after high energy density laser irradiation.Experiment ? The influence of Nd:YAG laser irradiation on the long-term dentin bond strength and nanoleakage of the bonding surfaceMethod:36 intact third molars were used. After the enamel of occlusal surfaces was removed, they were randomly divided into three groups. For the experimental groups, the dentin surfaces were treated with 1 w, 85J/cm2 (high energy density group) or 4w, 3501/cm2 (low energy density group) Nd:YAG laser irradiation before adhesion step, specimens without any treatment served as control. Then each group was divided into two sub-groups and bonded using a self-etching adhesive agent (G-Bond, GC) or etch-and-rinse adhesive agent (Single Bond 2,3M ESPE) respectively. After 10000 cycles thermocycling treatment the micro tensile bond strengths, failure modes analysis and nanoleakage evaluation were conducted.Results:after thermalcycling aging treatment, MTBS of all the groups were decreased except the low energy density laser treatment combining with etch-and-rinse adhesive group. After aging treatment, in the etch-and-rinse adhesive groups, the MTBS of low energy density laser irradiated samples was significant higher than the MTBS of samples without laser treatment (P<0.05). While the MTBS of high energy density laser irradiated samples had no significant differences with the MTBS of samples without laser treatment (P>0.05). In the self-etch adhesive groups, the MTBS of both low energy density and high energy density laser irradiated samples was decreased compared with the samples without laser treatment. After aging treatment, silver deposition of all the groups were decreased except the low energy density laser treatment combining with etch-and-rinse adhesive group.Experiment ? The exploration of the mechanism of enhanced durability of etch-and-rinse dentin bond strengths after low energy density Nd:YAG laser irradiation pre-treatmentMethod:15 intact third molars were used.2mm thick, flat slices were prepared from the mid-coronal dentin, they were randomly divided into two groups. Untreated dentin surfaces (control) and those treated with Nd:YAG laser at a setting of 1W,85J/cm2, 10 Hz were prepared. Dentin slices were prepared to examine alterations of dentin surface properties with Scanning electron microscopy (SEM), Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD) and Knoop hardness test.30 molars were sectioned parallel to the occlusal plane and randomly divided into control and laser treated groups. Afterwards, resin were bonded to the dentin surface using a two-step etch-and-rinse adhesive (Adper Single Bond 2) and 72 beams of each group were made by sectioning them Then each group was divided into two subgroups (24h storage and NaOCl storage, n=36 each group), and the microtensile bond strengths (MTBS), failure modes analysis and nano leakage evaluation were conducted. The Masson's trichrome staining was used to assess the possible exposed dentin collagen of bonding interface.Result:After laser irradiation, the crystalline structure of dentin was constant when evaluated by XRD, and the Knoop hardness of dentin presented no significant changes. The results of ATR-FTIR and Masson's trichrome verified that laser irradiation partly removed collagen fibers from the dentin surface. Laser pretreatment did not influence short-term dentin bond strengths (p>0.05), but kept the dentin bond strengths from decreasing after NaOCl aging treatments compared with control group (p<0.05). Furthermore, after NaOCl aging treatments, the laser-treated group showed less silver deposition than the control (p<0.05).Conclusion:1. Low energy density laser irradiation which is usually applied to cure dental hyper sens itibeness will not influence the etch-and-rinse dentin bond strength, but will significantly decrease the self-etch dentin bond strength. While high energy density laser irradiation which is commonly used to remove caries and prepare cavity will decrease the self-etch dentin bond strength, but will not affect the etch-and-rinse dentin bond strength. High energy density laser irradiation will increase the nanoleakage of dentin bonding surface of both etch-and-rinse adhesive and self-etch adhesive agent.2. If using self-etch dentin adhesive agent, both low and high energy density laser irradiation will decrease the durability of dentin bond strength. On the contrary, low energy density laser irradiation combine with etch-and-rinse adhesive agent will enhance the durability of dentin bond strength, and decrease the nanoleakage of dentin-and-resin bond surface. High energy density laser irradiation will not significantly influence the durability of etch-and-rinse dentin bond strength.3. Considering both immediate and long-term effect of dentin bond strength, etch-and-rinse adhesive agent will be a better choice after laser irradiation. And when using laser irradiation on the dentin surface, a lower energy output will reduce the nanoleakage of dentin bond surface.