| Objective:To evaluate the effect of different surface-wet protocols on the structure of dentin collagen network, effect of ethanol-wet bonding with hydrophobic adhesive on different dentin substrates, and its influence on dentin bonding durability. The present study includes three parts:Part one-Observation of dentin collagen structure after different surface treatments by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM); Part two-Effect of ethanol-wet bonding with hydrophobic adhesive on different dentin substrates; and Part three-Effect of ethanol-wet bonding with hydrophobic adhesive on dentin bonding durability.PART ONEEffect of different surface-wet protocols on the structure of dentin collagen networkExp.1 Observation of dentin collagen network after different surface treatments Materials and Methods:Polished human dentin surfaces were etched with phosphoric acid and water rinsed. Tested protocols were:(1) water-rinse (control); (2) 100% ethanol-rinse (20 s); (3) 100% ethanol-rinse (3 x 20 s); (4) 100% ethanol-rinse (3×1 min); and (5) progressive ethanol replacement (50-100%). Surface topography was observed with FESEM and AFM.Results:As water was gradually replaced by ethanol, the interfibrillar spaces of collagen network significantly increased, and the collagen matrix was in fully extended state. However, the ethanol-treated collagen matrix was likely to collapse faster than water-saturated dentin in atmosphere, which created smoother 3D surface topography under AFM.PART TWOEffect of ethanol-wet bonding with hydrophobic adhesive on different dentin substrates Exp.2 Effect of ethanol-wet bonding with hydrophobic adhesive on sound and caries-affected dentinMaterials and Methods:Thirty-two extracted carious human molars were stained by caries detector and ground to expose flat surfaces where the caries lesion was surrounded by normal dentine. In the control groups, prepared sound dentin (SD) and caries-affected dentin (CAD) were bonded with AdperTM Single Bond 2 by traditional water-wet bonding technique. In the experimental groups, specimens were treated as follow:Group 1 and Group 2 used 100% ethanol, applied either in one or in three 20 s step, respectively. Group 3, rinsed with stepwise ethanol dehydration; Micro-tensile bond strength (μTBS) test was used to evaluate bonding effects. Element analysis and microhardness of debonded dentin surfaces was measured to ensure CAD presence. Interfacial nanoleakage was evaluated by field emission scanning electron microscopy.Results:Treatment significantly improvedμTBS in CAD in Groups 2 and 3, while had no effect on Group 1. Conversely, treatment significantly reducedμTBS in SD in Groups 1 and 2, while it had no effect in Group 3. Nanoleakage presence varied with ethanol-wet protocols. Significantly lower microhardness was detected in CAD than that in SD. Element analysis results revealed that significant changes in Mg, Zn, Na, and Mn content in CAD and SD.Exp.3 Implications of different ethanol wet-bonding protocols on bonding hydrophobic adhesive to intraradicular dentinMaterials and Methods:One hundred-twenty flat dentin slices from human premolar roots were randomly assigned to five groups (n= 24). All specimen surfaces were acid-etched, rinsed, and left moist. For the control group, the slices were bonded with a three-step etch-and-rinse adhesive (AdperTM ScotchbondTM Multi-Purpose). For the other four experimental groups, the slices were treated with different ethanol-wet bonding protocols before application of hydrophobic adhesive:Groups 1,2, and 3 used 100% ethanol with 20 s,3 x 20 s or 3 x 60 s applications, respectively; Group 4 used a series of increasing ethanol concentrations:50%,70%,80%,95% and three 100%,30 s for each application. Nano-scale adhesion force, shear bond strength and nanoleakage expression were evaluated.Results:Nano-scale adhesion forces were different among all groups with remarkably reduction in ethanol dehydrated groups (P< 0.001). The shear bond strength of Group 1 was significantly lower than that of other groups (P< 0.05); Group 2 and 3 were similar with the control group (P> 0.05); while Group 4 exhibited higher bond strength than the control group (P<0.05). Reduced nanoleakage was manifested in all groups with ethanol-wet protocols except Group 1.Exp.4 Effect of ethanol-wet bonding with hydrophobic adhesive on microleakage Materials and Methods:Twenty teeth with class V cavities were etched with phosphoric acid and water rinsed. In the control group, prepared specimens were bonded with AdperTM Single Bond 2 by traditional water-wet bonding technique. In the other two experimental groups, the specimens were treated with different ethanol-wet bonding protocols before application of hydrophobic adhesive:Groups 1, 2, and 3 used 100% ethanol with one 20 s,3×20 s or 3×60 s applications, respectively; Group 4 used a series of increasing ethanol concentrations:50%,70%, 80%,95% and three 100%,30 s for each application. All cavities were restored with a light-cured composite. After immersion in a 0.5% fuchsine solution, three sections were obtained from each specimen and observed under a stereomicroscope. Occlusal and gingival microleakage were evaluated with a four-steps scoring system, respectively. The microleakage scores were analyzed with the Kruskal-Wallis ANOVA and the Mann-Whitney test with Bonferroni’s correction. Occlusal and gingival microleakage were compared with the Wilcoxon test.Results:The statistical analysis showed significant differences in microleakage among groups (P< 0.05) and significant differences between the occlusal and gingival microleakage were also detected (P< 0.05). The occlusal microleakage was higher than the gingival (P< 0.05), and the microleakage significantly decreased in Group 4 (P< 0.05).PART THREEEffect of ethanol-wet bonding with hydrophobic adhesive on dentin bonding durabilityExp.5 Histomorphologic characterization and bond strength evaluation of resin-dentin bonds to water-vs. ethanol-saturated caries-affected and sound dentin after agingMaterials and Methods:Forty-eight extracted carious human molars were stained by caries detector and ground to expose flat surfaces where the caries lesion was surrounded by normal dentine. In the control groups, prepared sound dentin (SD) and caries-affected dentin (CAD) were bonded with AdperTM Single Bond 2 by traditional water-wet bonding technique. In the experimental groups, specimens were treated as follow:Group 1 used 100% ethanol, applied in three 20 s step. Group 2 rinsed with stepwise ethanol dehydration; Resin-dentin bonded interfaces (0.81 mm2) were stored in distilled water for 24 h or 6 months and subjected to microtensile bond strength evaluation. Interfacial nanoleakage evaluation was performed by field emission scanning electron microscopy (FESEM). Resin-dentin bonded sections (10μm thick) were stained with Masson’s trichrome and examined using light microscopy. Collagen exposure and adhesive penetration were examined qualitatively.Results:The control groups exhibited significant reduction in microtensile bond strength after aging regardless of the dentin substrate (P< 0.05). Hybrid layer degradation was evident in all specimens examined by FESEM. An increase in the exposed collagen zone was also observed in CAD interfaces. The hydrophobic adhesive with ethanol-wet bonding preserved bond strength in Groups 1 and 2 (P> 0.05). Hybrid layer integrity was well preserved in Group 2 in SD and CAD. Conclusions:1. The structure of demineralized collagen matrix varied with different surface wet protocols. Ethanol treatments could dehydrate the acid-etched dentin which produced larger interfibrillar spaces and extended the collagen network. However, ethanol replacement must be meticulously performed to prevent water-saturated collagen being exposed to air. The surface tension present along the air-collagen interface can easily result in collapse of the collagen matrix. Therefore, the ethanol-wet bonding is technique-sensitive in its implementation.2. Ethanol-wet bonding can potentially improve bond efficacy and reduce leakage phenomenon to caries-affected dentin and intraradicular dentin when a proper protocol is used, which may be beneficial to clinical outcomes.3. Coaxing hydrophobic resins into acid-etched dentin using proper ethanol-wet bonding techniques preserves resin-dentin bond strength and interface structural integrity for at least six months in vitro. It is speculated that the longevity of bonding restorations could be improved.4. Resin-dentin bonding is far more complex than most dentists realize. To explore the mechanisms of resin-dentin bond degradation and a combination of several of anti-degradation strategies should result in overcoming the critical barriers to progress currently encountered in dentin bonding. |
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