Journal of Dental Research, Vol 72, 1434-1442, Copyright © 1993 by International & American Associations for Dental Research Online Journals

ARTICLES

Assessment by nano-indentation of the hardness and elasticity of the resin-dentin bonding area

B. Van Meerbeek, G. Willems, J. P. Celis, J. R. Roos, M. Braem, P. Lambrechts and G. Vanherle
Department of Operative Dentistry and Dental Materials, Katholieke Universiteit te Leuven, Belgium.

The hardness and Young's modulus of the successive layers across a resin-dentin bonding area were determined by nano-indentation for four commercially-available dentin adhesive systems, of which two were also applied with a different conditioning agent. With a computer-controlled nano-indentation technique, minute triangular indentations were made within a small area of a few micrometers' diameter at a load of a few milli-Newtons. The load and displacement of the indenter were continuously monitored during the loading-unloading sequence, so hardness and Young's modulus could be computed as a function of the indenter geometry and the applied load. The hardness of the resin-dentin interdiffusion zone was significantly lower than that of unaltered dentin. A gradient of moduli of elasticity was observed from the rather stiff dentin over a more elastic resin-dentin interdiffusion zone and adhesive resin layer to the restorative composite. That gradient was more substantial in those systems that produced relatively thick adhesive resin layers or supplementally provided a filled low-viscosity resin as an intermediate layer between the adhesive resin and the bulk restorative composite. Such an elastic bonding area might have a strain capacity sufficient to relieve stresses between the shrinking composite restoration and the rigid dentin substrate, thereby improving the conservation of the dentin bond and, as a consequence, the marginal integrity and retention of the restoration.

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