BONDING TO ENAMEL WITH ETHANOL-WET BONDING TECHNIQUE

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It is well-known that resin-dentin bond degrades by the time as a results of poor quality of dentinal hybrid layers made with conventional-wet bonding technique, namely, water-wet bonding technique.¹ Ethanol-wet bonding is a novel bonding technique was developed to improve the quality of dentinal hybrid layers of resin adhesives.² Ethanol application/treatment on water-wet acid-etched dentin surfaces, removes water from interface without causing collapse of demineralized dentin matrices prior infiltration of resin monomers, thus enhancing resin infiltration in the resultant hybrid layers.^1,2 It was shown that durability of resin-dentin bonds made with different resin adhesives by using ethanol-wet bonding techniques were better than those of conventional bonding technique.^3,4

Although ethanol-wet bonding has advantages for improving resin-dentin bond durability, it also requires additional steps and time for bonding procedure. Additionally, when dentin is wetted with ethanol, it is difficult to keep the enamel wet with water or even dry. If the enamel can be bonded effectively while it is wet with ethanol, the overall dentin-bonding procedure using ethanol-wet-bonding can be significantly simplified. However, the effects and potential benefits of ethanol-wet bonding on resin-enamel bonds and resin-enamel interfaces are not well-understood. Therefore, the effects of ethanol wet bonding on resin enamel bonds and interface morphology were assessed in comparison with conventional wet bonding technique (water-wet bonding) in the present study.

We assessed application of absolute ethanol for 1 min on resin-enamel bond strengths of two commercially available etch-and-rinse adhesives (Single Bond 2, 3M ESPE, St. Paul, MN, USA; and All bond 3, Bisco Inc., Schaumburg, IL, USA) by means of microtensile bond strength test. Single Bond 2 is a simplified etch-and-rinse adhesive, and All bond 3 is a traditional three-step etch-and-rinse adhesive. Also quality of resin-enamel interfaces were evaluated under scanning electron microscopy (SEM). Bond strength data were analyzed with two-way analysis of variance (ANOVA) and a least significant differences (LSD) test was used for post-hoc comparisons (p < 0.05).

Our findings suggested that ethanol-wet bonding could improve resin-enamel bond strengths of both of tested adhesives. Ethanol-wet bonding increased enamel bond strength of All Bond 3 from 26.4 (5.4) MPa to 31 (7.3) MPa when compared with conventional wet bonding technique. However, ethanol-wet bonding had a significant benefit on resin-enamel bond strength of Single Bond 2. Ethanol-wet bonding increased enamel bond strength of Single Bond 2 from 17.4 (4.6) MPA to 28.7 (7.6) MPa when compared with conventional wet bonding technique. SEM micrographs of Single Bond 2 applied to etched-enamel-wet with absolute ethanol showed longer and smoother resin tag formations. It seems that resin had penetrated into deeper interprismatic areas when applied with ethanol-wet bonding technique. However, SEM micrographs of All Bond 3 applied to etched-enamel-wet with absolute ethanol also showed better resin tag formations than those of the water-wet bonding groups.

Resin monomers used in the current adhesive systems have better solubility in ethanol than that of water. However, it is known that water would inhibit polymerization of resin monomers.⁵ It was reported that hydrophobic monomer Bis-GMA yields to phase separation upon to contact with water.⁶ This impedes resin infiltration into acid-etched dentin, and results in poor quality of dentin hybrid layers. However, Bis-GMA has better miscibility in the ethanol. Single Bond 2 is a simplified etch-and-rinse adhesive, consist of resin monomers for priming and bonding processes. BisGMA is a hydrophobic resin monomer within Single Bond 2 for bonding to hydrophobic resin composite. Therefore, replacing water from acid-etched enamel with ethanol application by using absolute ethanol for 1 minute, prior to resin monomer infiltration into acid-etched enamel would provide prevent phase separation of Single Bond 2 and provide a benefit for resin bond strength and quality of resin-enamel interfaces. It was found that ethanol-wet bonding almost doubled resin-enamel bond strength of Single Bond 2. However, All bond 3 is a traditional three-step etch-and-rinse adhesives, and Bis-GMA is absent its primer solution which infiltrates into the acid-etched dentin. Insignificant improvement was detected in enamel bond strength of All bond 3. Therefore, the findings of the present study supported the benefits of ethanol-wet bonding when used for enamel bonding.

In conclusion, our study demonstrated that ethanol-wet bonding had a potential to improve resin-enamel hybridization as result of inhibition of phase separation of adhesive resin systems, thus achieving better resin infiltration in the ethanol-wet acid-etched enamel. However, it should be noted that the ethanol-wet bonding may be used on dentin and enamel simultaneously and may provide more durable resin-dentin bonds, due to the more-qualified resin-enamel hybridization zone made with ethanol-wet bonding.