Bonding agents monomer HEMA

Of particular concern in these studies has been the presence of 2 hydroxethyl methacrylate (HEMA). This has been shown experimentally to be able to diffuse through the pulp chamber when released from a bonding agent placed beneath a composite resin (Hamid and Hume 1997). Thickness made a difference to the rate of diffusion, but even relatively thick layers of dentin (i.e., in the range 3.4—3.6 mm) were not sufficient to eliminate it completely. Another finding of significance was that diffusion of HEMA was much more rapid in teeth that had been severely affected by caries. In other words, the reason that tooth repair is needed clinically, caries, turns out to be responsible for affecting dentine permeability adversely, and opens the way for potentially harmful monomers to reach the pulp. 

HEMA and other monomers used in bonding agents have been shown to be cytotoxic (Hume and Gerzina 1996). They inhibit cell proliferation and decrease mitochondrial activity significantly. The latter means that energy transduction processes in the living cells are affected adversely. 

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