Effects of Ionic Flow and Amelogenins on the Lengthwise Growth of Octacalcium Phosphate Crystals in a Model System of Tooth Enamel Formation

Abstract : This paper briefly reviews our recent studies which aimed to investigate the effects of 1) the Ca(exp 2+) and PO4(exp 3-) 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 groan at 37 degrees 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 arid 2) extracted bovine amelogenin arid recombinant murine amelogenins (rM179, rM166). With an increase in the amount of Ca(exp 2+) and/or PO4(3-) 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 arid 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 arid 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.