A number of mechanisms (both mechanical and chemical) have been proposed as the cause of dentin adhesion. Extensive research in Japan during the past 10 years has shown that strong, long‐lived bonds between resin and living dentin will form when a monomer such as 4‐META, which contains both hydrophilic and hydrophobic chemical groups, penetrates the tissue and polymerizes in situ. This resin‐impregnation creates a transitional “hybrid” layer, that is neither resin nor tooth, but a hybrid of the two. The thin layer of resin‐reinforced dentin locks the two dissimilar substances together on a molecular level, sealing the surface against leakage and imparting a high degree of acid resistance.

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