Effects of Ionic Flow and Amelogenins on the Lengthwise Growth of Octacalcium Phosphate Crystals in a Model System of To
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Effects of Ionic Flow and Amelogenins on the Lengthwise Growth of Octacalcium Phosphate Crystals in a Model System of Tooth Enamel Formation.
M. Iijima1 , Y. Moriwaki 1, H.B. Wen 2# , T. Takagi 3, A.G. Fincham 2 and J. Moradian-Oldak 2 1 Asahi University School of Dentistry, Dental Materials and Technology, 1851-1 Hozumi, Hozumi-cho, Motosugun, Gifu 501-0296, Japan. 2 University of Southern California, School of Dentistry, Center for Craniofacial Molecular Biology, USA. # Present Affiliation : DePuy, a Johnson & Johnson company. 3 Tokyo Medical and Dental University, School of Dentistry, Oral Biology, Japan. ABSTRACT This paper briefly reviews our recent studies, which aimed to investigate the effects of 1) the Ca2+ and PO43- ions flow and 2) amelogenins on the lengthwise growth of octacalcium phosphate (OCP), which is a potent precursor of enamel apatite crystal. OCP crystals were grown at 37°C in a dual membrane system under various amount of ionic inflow into a reaction space, using 1) 5-30mM Ca and PO4 solutions as ionic sources and 2) extracted bovine amelogenin and recombinant murine amelogenins (rM179, rM166). With an increase in the amount of Ca2+ and/or PO43- ions flow, the length of OCP crystal increased, while the width decreased. As a result, the length to width (L/W) ratio of crystal changed from 3 to 95, while the width to thickness (W/T) ratio from 32 to 9. The effect of amelogenins was unique, regardless of the type of amelogenins : Rod-like and prism-like OCP crystals with large L/W (61~107) and small W/T (1.3~2.2) ratios were formed in 10% amelogenin gels. In contrast, characteristic ribbon-like OCP crystals grew without protein and with gelatin, albumin, polyacrylamide gel and agarose gel. Specific interaction of amelogenins with OCP crystal was ascribed to the self-assembly property of amelogenin molecules and their hydrophobic nature. It was suggested that ionic flow and amelogenins play some critical roles in the elongated growth of enamel crystals. INTRODUCTION Enamel crystals of mammalian tooth are formed in an enamel matrix, which is abundant in amelogenins, under regulated Ca2+ and PO43- ion supply from the layer of ameloblasts. In the early stage of the enamel crystal formation, very long and thin crystallites deposit in an enamel matrix with their long axis parallel to each other. In the later stage, crystals mainly increase their width and thickness, and grow into flat-hexagonal prisms [1,2]. The morphology is quite different from the irregular shaped plate-like morphology of bone and dentin crystals. We speculate that the uniqueness of enamel crystals relates to their growth condition : 1) lattice ions of enamel crystals, Ca2+ and PO43- ions, are transported from the layer of ameloblasts into the enamel matrix, which might cause ionic flow, and the mode of the ionic flow changes during the tooth enamel formation [3,4] ; 2) molecules of amelogenin, which is major component of enamel proteins [5,6] and highly hydrophobic [7], assemble into nanospheres and form gel [8-10] with uni
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