Application of amino acid derivative monomer on dentin adhesion and

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In this study, several kinds of amino-acid monomers with different molecular structure were newly synthesized and their effect on the adhesion between resin and tooth was investigated to clarify the relation between the bonding effectiveness and molecular structure of adhesive monomer.Firstly, N-acryloyl aspartic acid (N-AAsp) was synthesized by the reaction between acrylic chloride and DL-aspartic acid. N-AAsp can be dissolved in distilled water up to 25wt%. The maximum bond strength to enamel and dentin, 16 MPa, was obtained when 20wt% N-AAsp aqueous solution was used as a self-etching primer.Secondly, the bonding efficacy of N-acryloy Glycine (N-AGly) having one carboxyl group to dentin was estimated, comparing with that of N-AAsp having two carboxyl groups. As a result, N-AAsp was more effective on dentin bonding.In addition, N-acryloyl Glutamic acid (N-AGlu) was synthesized. N-AGlu has two carboxyl groups and same structure of the principal chain as N-AAsp, but the structure of side chain is different. The pKa values of the carboxyl group in the side chain of N-AGlu and N-AAsp were 4.53 and 4.19, respectively. The N-AGlu exhibited no bonding efficacy on the ground dentin surface, whereas N-AAsp present good efficacy. On the other hand, N-AGlu showed bonding effect equal with the N-AAsp when it was applied on the dentin after the smear layer was removed.Our results indicate that the amino-acid monomers having two carboxyl groups have good potential value as a self-etching primer for bonding to tooth. The results also suggest that the pKa value of carboxyl group in monomer molecules is important factor in the appearance of dentine adhesive property.