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FIC. 10. Reactive monomer structures for bonding to calcific tissues. M-R, monomer portion of molecule. (After Asmussen, E., Aranjo, P. A., and Pentsfeld, A. 1989, Trans. Acad. Dent. Mater. 2: .59.)

porosity in the surface (Fig. 4). A primer treatment is then applied that comprises a reactive monomer system (Fig. 10) containing a carboxylate or a polyphosphate function, depending on the type of product. These primers also contain hydro-philic monomers, such as hydroxyethyl methacrylate (HEMA), and may also contain water.

The function of the primer is to penetrate the demineral-ized dentin surface and facilitate wetting by an unfilled dimethacrylate bonding resin which is subsequently applied. Polymerization of this treatment layer by visible light activation results in the formation of micromechanical bonds by penetration into the dentin and surface tubules, forming the so-called hybrid layer (Nakabayashi et al., 1991) or resin-interdiffusion zone (Van Meerbeck et al., 1992). Chemical interaction with the hydroxy apatite and/or proteinaceous phases of the dentin surface may also occur (Asmussen and Hansen, 1993). However, direct chemical evidence has not been provided yet for the postulated interactions (Eliades, 1993). Under the best conditions, initial tensile bond strengths of 15-25 MPa can be obtained depending on test conditions. The long-term durability of these bonds under oral conditions is being investigated.

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