| Non-carious sclerotic dentin, as a kind of pathological dentine, is mainly attributed to the loss of tooth tissue by attrition, which is usually located in the cervical wedge-shaped defect, the severe abrasion area and the dentine hypersensitivity area of tooth. And it is always positively correlated with individual age. Therefore, up to now, it has become a kind of important oral diseases, which severely influences the quality of the elderly. With regard to this pathological dentin, clinically, silicon carbide burs pretreatment and acid etching are always used followed by resin composite restoration. However, the restoration shows the poor long-term effect because of the special structure of non-carious sclerotic dentin. And some researchers have reported that the bonding effect of non-carious sclerotic dentin shows 26%-30% lower than the sound dentin. The conventional methods, which include polishing, etching and the chemical ways, couldn’t effectively improve the bonding effect of non-carious sclerotic dentin. Then it’s very necessary to improve the bonding effect efficiently between the non-carious sclerotic dentin and composite resin.Er,Cr:YSGG laser, as a new type of powered hydrodynamic system, could effectively remove the tooth hard tissue. Some reports have suggested Er,Cr:YSGG laser could improve the bonding effect of the non-carious sclerotic dentin by roughening the surface, opening the obstructed dentinal tubules and removing the smear layer. However, the output power of Er,Cr:YSGG laser for non-carious sclerotic dentin was always referred to which for enamel. Although the above materials are both highly mineralized as well as the similarity transparent, they have completely different structures. Therefore, nobody concerns whether the power of Er,Cr:YSGG laser for enamel is also the optimal power for non-carious sclerotic dentin. So this question should be further studied.The purpose of the present study based on the above problem was to comprehensively evaluate the effect of Er,Cr:YSGG laser pretreatment at various output powers(1W, 2W, 3W, 4W, 5W, 6W) on the bonding performance of non-carious sclerotic dentin via observing the surface micromorphology of the pretreated non-carious sclerotic dentin with FESEM as well as the micromorphology of bonding interface assessing the bond strength with micro-shear bond strength, analyzing the marginal seal ability by dye penetration with silver-ammonia solution. And then this study can provide the optimal output power of Er,Cr:YSGG laser for non-carious sclerotic dentin to some extent, in order to obtain the ideal surface pretreatment for non-carious sclerotic dentin.The present study could be devided into three experiments. In experiment 1, we observe the surface micromorphology of the pretreated non-carious sclerotic dentin. In experiment 2, We intended to evaluate the effect of Er,Cr:YSGG laser pretreatment at different output powers on the bonding strength between resin composite and non-carious sclerotic dentin. As for the experiment 3, we assessed the effect of Er,Cr:YSGG laser pretreatment at different output powers on the marginal sealing ability of bonding interface.Experiment 1 was focused on the measurement of surface roughness in each group and observation of the surface micromorphology with FESEM, meanwhile, using the software Image Pro plus 6.0 to calculate the open area rate of dentinal tubules in FESEM images. The final results verified that the different power lasers could obviously influence the the surface micromorphology of non-carious sclerotic dentin. For all the groups, the untreated control group and acid etching group obtained the minimal roughness values(p<0.05), with the increase of the output power(from 1W to 4W) of laser, the roughness value was incremental, and the 4W group showed the highest roughness value(p<0.05), while the roughness value was diminishing(from 4W to 6W). In addition, according to the FESEM images and the open area rate of dentinal tubules, we could also see with the increase of laser output power, the open area of dentinal tubules was increased gradually, and the open area rates of dentinal tubules in the 4W, 5W and 6W groups showed no significant difference(p>0.05).In experiment 2, the bonding strengths between resin composite and the pretreated non-carious sclerotic dentin wre measured and analyzed. Furthermore, the micromorphology of the bonding interface in each group was observed with FESEM. The results showed that the different output powers of Er,Cr:YSGG laser indeed had the different effects on the bonding strengths between resin composite and the pretreated non-carious sclerotic dentin. As far as the immediate bonding strengths, the 4W output power obtained the highest bonding strength, which was significantly higher than other Er,Cr:YSGG laser pretreatment groups(p<0.05), the latter groups showed no significant differences(p>0.05). The untreated control group showed the lowest bonding strength, which was significantly lower than the groups for diamond bur, 3W and 4W(p<0.05) while had no significant differences compared with other groups(p>0.05). After thermocycling, the 4W group still achieved the highest bonding strength, which, however, was not significantly different with the groups for diamond bur, 1W, 2W, 3W and 5W(p>0.05), and remarkably higher than the groups for untreated control and 6W(p<0.05), the untreated control group had the lowest bonding strength. For the micromorphology of the bonding interface, the gap in the interface of thermolcycling control subgroup could be clearly seen, while there had the similar resin tags in immediate and thermolcycling interface. Both the quantity and roughness of resin tags were increased with the rise of Er,Cr:YSGG laser output power. And the quantities of resin tags in control and diamond bur groups were significantly less than the Er,Cr:YSGG laser groups.In experiment 3, the dye penetration with silver-ammonia solution was used to evaluate the immediate and durable sealing ability of the bonding interface between resin composite and non-carious sclerotic dentin. The result affirmed the different output powers could obviously affect the sealing ability of the bonding interface. In the immediate groups, the 4W group obtained the optimal sealing ability, which, however, showed no significant difference with the 5W group(p>0.05), the untreated control group and 1W Er,Cr:YSGG laser group showed the worst sealing ability. After thermocycling, the groups for 4W, 5W, 6W and diamond bur achieved the better sealing ability while the rest groups obtained the worse one. |
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