Fluoride encapsulation in calcium matrix

Abstract

Fluoride ion (F-) is an important ingredient in a toothpaste. It protects caries by reacting with hydroxyapatite [Ca10(PO)4(OH)2] in tooth enamel to form insoluble fluorapatite [Ca10(PO)4(F)2]. Unfortunately, F- also easily interacts with calcium species in a toothpaste, and then it is deactivated. In this work, we focus on the encapsulation of F- in a shellac bead by using a simple extrusion method. To construct shellac beads, an aqueous solution of F- is injected into an ethanolic solution of shellac. The shellac beads are formed due to insolubility of shellac in water. Then, the beads are transferred into DI water for hardening a bead wall via a diffusion of ethanol in the bead wall to an aqueous phase. The bead formation mechanism is investigated using infrared spectroscopy. The process is also optimized by varying shellac concentration, shellac-dissolution time, bead-formation time, and bead-hardening time. The average size of F--encapsulated shellac beads is 2.59 ± 0.33 mm. Active F- is completely released from shellac beads after immersed in DI water for 14 days. Surprisingly, after immersed in 5 % CaCl2, the beads can encapsulate the active F- for, at least, 3 months with the percentage of active F- remaining in the beads of 71.03 ± 4.18 %. It is because CaF2 can block releasing channels of active F- on the bead surface.