Six-month evaluation of adhesives interface created by a hydrophobic adhesive to acid-etched ethanol-wet bonded dentine with simplified dehydration protocols

Abstract 

Objectives

To evaluate the efficacy of simplified dehydration protocols, in the absence of tubular occlusion, on bond strength and interfacial nanoleakage of a hydrophobic experimental adhesive blend to acid-etched, ethanol-dehydrated dentine immediately and after 6 months.

Methods

Molars were randomly assigned to 6 treatment groups (n=5). Under pulpal pressure simulation, dentine crowns were acid-etched with 35% H₃PO₄ and rinsed with water. Adper Scotchbond Multi-Purpose was used for the control group. The remaining groups had their dentine surface dehydrated with ethanol solutions: group 1=50%, 70%, 80%, 95% and 3×100%, 30s for each application; group 2 the same ethanol sequence with 15s for each solution; groups 3, 4 and 5 used 100% ethanol only, applied in seven, three or one 30s step, respectively. After dehydration, a primer (50% BisGMA+TEGDMA, 50% ethanol) was used, followed by the neat comonomer adhesive application. Resin composite build-ups were then prepared using an incremental technique. Specimens were stored for 24h, sectioned into beams and stressed to failure after 24h or after 6 months of artificial ageing. Interfacial silver leakage evaluation was performed for both storage periods (n=5 per subgroup).

Results

Group 1 showed higher bond strengths at 24h or after 6 months of ageing (45.6±5.9^a/43.1±3.2^aMPa) and lower silver impregnation. Bond strength results were statistically similar to control group (41.2±3.3^ab/38.3±4.0^abMPa), group 2 (40.0±3.1^ab/38.6±3.2^abMPa), and group 3 at 24h (35.5±4.3^abMPa). Groups 4 (34.6±5.7^bc/25.9±4.1^cMPa) and 5 (24.7±4.9^c/18.2±4.2^cMPa) resulted in lower bond strengths, extensive interfacial nanoleakage and more prominent reductions (up to 25%) in bond strengths after 6 months of ageing.

Conclusions

Simplified dehydration protocols using one or three 100% ethanol applications should be avoided for the ethanol-wet bonding technique in the absence of tubular occlusion, as they showed decreased bond strength, more severe nanoleakage and reduced bond stability over time.

Keywords: Bond strength, Interfacial nanoleakage, Ethanol-wet bonding, Dentine