Assessment of the quality of resin-dentin bonded interfaces: An AFM nano-indentation, mu TBS and confocal ultramorphology study

Objective. The aim of this study was to assess by using confocal microscopy (CLSM), AFM nano-indentation and microtensile bond strength test (mu TBS) the quality of the resin-dentin interfaces created with selected bonding parameters.

Methods. Dentin conditioned with H3PO4 or EDTA was bonded in ethanol- or water-wet condition using a HEMA-free or HEMA-containing adhesive. The resin-bonded teeth were stored in distilled water (24 h) and sectioned as match-sticks (0.9 mm(2)) for mu TBS. Further resin-bonded teeth were sectioned and analyzed using CLSM, and AFM nano-indentation. The AFM imaging and nano-indentation processes were undertaken using a Berkovich diamond indenter. The modulus of elasticity (Ei) and hardness (Hi) across the interface were evaluated with the specimens in a fully hydrated status. The AFM imaging was performed both in dry and wet conditions for evaluating the shrinkage of the hybrid layer on dehydration.

Results. The HEMA-containing adhesive applied onto H3PO4-etched ethanol or water-wet dentin created hybrid layers with the lowest biomechanical nano-properties (p <0.05); no significant differences in mu TBS were found between the two wet-bonding techniques (p > 0.05). However, the ethanol- wet bonding reduced the dye penetration into the adhesive layer created with the HEMA-containing adhesive. Hybrid layers with high biomechanical properties, low micropermeability and no shrinkage were only possible when using HEMA-free adhesive applied in ethanol wet-dentin. In particular, a significant increase in Ei and Hi was achieved at the hybrid layer and underneath the resin-dentin interface of ethanol-wet EDTA-treated dentin.

Significance. The use of HEMA-free adhesives applied onto ethanol-wet dentin may be considered as an alternative and suitable bonding strategy to achieve high quality resin-dentin interfaces. (c) 2012 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.