Chemical interaction of glycero-phosphate dimethacrylate (GPDM) with hydroxyapatite and dentin |
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| Authors: | Kumiko Yoshihara Noriyuki Nagaoka Satoshi Hayakawa Takumi Okihara Yasuhiro Yoshida Bart Van Meerbeek |
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| Affiliation: | 1. Center for Innovative Clinical Medicine, Okayama University Hospital, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan;2. Advanced Research Center for Oral and Craniofacial Sciences, Okayama University Dental School, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan;3. Biomaterials Laboratory, Graduate School of Interdisciplinary Science and Engineering in Health Systems, Okayama University, 3-1-1, Tsushimanaka, Kita-ku, Okayama 700-8530, Japan;4. Division of Applied Chemistry, Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima-Naka, Kita-ku, Okayama 700-8530, Japan;5. Department of Biomaterials and Bioengineering, Faculty of Dental Medicine, Hokkaido University, Kita 13, Nishi 7, Kita-ku, Sapporo, Hokkaido, 060-8586 Japan;6. KU Leuven (University of Leuven), Department of Oral Health Research, BIOMAT, & University Hospitals Leuven, Dentistry, Kapucijnenvoer 7, Block A — Box 7001, BE-3000 Leuven, Belgium |
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| Abstract: | ObjectivesAlthough the functional monomer glycero-phosphate dimethacrylate (GPDM) has since long been used in several dental adhesives and more recently in self-adhesive composite cements and restoratives, its mechanism of chemical adhesion to hydroxyapatite (HAp) is still unknown. We therefore investigated the chemical interaction of GPDM with HAp using diverse chemical analyzers and ultra-structurally characterized the interface of a GPDM-based primer formulation with dentin.MethodsHAp particles were added to a GPDM solution for various periods, upon which they were thoroughly washed with ethanol and water prior to being air-dried. As control, 10-methacryloyloxydecyl dihydrogen phosphate (MDP) was used. The molecular interaction of GPDM with HAp was analyzed using X-ray diffraction (XRD) and solid-state nuclear magnetic resonance (NMR) spectroscopy. Crystal formation upon application of GPDM onto dentin was analyzed using thin-film XRD (TF-XRD). Its hydrophobicity was measured using contact-angle measurement. The interaction of GPDM with dentin was characterized using transmission electron microscopy (TEM).ResultsXRD revealed the deposition of dicalcium phosphate dihydrate (DCPD: CaHPO4·2H2O) on HAp after 24 h. NMR confirmed the adsorption of GPDM onto HAp. However, GPDM was easily removed after washing with water, unlike MDP that remained adhered to HAp. Dentin treated with GPDM appeared more hydrophilic compared to dentin treated with MDP. TEM disclosed exposed collagen in the hybrid layer produced by the GPDM-based primer formulation. Significance: Although GPDM adsorbed to HAp, it did not form a stable calcium salt. The bond between GPDM and HAp was weak, unlike the strong bond formed by MDP to HAp. Due to its high hydrophilicity, GPDM might be an adequate monomer for an etch-and-rinse adhesive, but appears less appropriate for a ‘mild’ self-etch adhesive that besides micro-retention ionically interacts with HAp, or for a self-adhesive restorative material. |
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| Keywords: | Functional monomer NMR XRD TEM Apatite Dentin |
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