A Study on Interaction Dynamics and Effect of Temperature on Hydroxyapatite- Fluoride Interface

The amount of fluoride adsorbed onto hydroxyapatite increased as the aqueous fluoride concentration increased. When the aqueous fluoride concentration exceeded 100 ppm, the total amount of fluoride adsorbed onto hydroxyapatite decreased after being washed off with water three times. It is postulated that when the aqueous fluoride concentration exceeds 100 ppm, a multilayer structure of calcium fluoride formed around hydroxyapatite is washed off, resulting in the decrease of the fluoride adsorbed onto hydroxyapatite. It is also postulated that the fluoride multilayer consists of calcium fluoridecomplex whose interaction force is weaker than ionic force created by replacing OHwith FOne can rinse his/her mouth with fluoride solution of less than 100 ppm, 20 to 30 ppm preferably. And then one should rinse the mouth with water several times so as to achieve the fluoride concentration of 0.5 to 1 ppm in the mouth which is the WHO recommended fluoride concentration in drinking water. The thermodynamic study revealed that Langmuir isotherm can be applied for the adsorption of fluoride onto hydroxyapatite. The thermodynamic parameters indicated that the adsorption process is spontaneous and endothermic. The high degree of disorderliness exists between solid – solution interface upon the adsorption of fluoride onto hydroxyapatite.