Kinetics of dissolution of calcium hydroxyapatite: VI. The effects of adsorption of methylene diphosphonate, stannous ions and partly-peptized collagen

Abstract

Kinetic effects of the rate of dissolution of calcium hydroxyapatite crystals (HAP) due to adsorption of methylene diphosphonate ions (MDP), stannous ions, partly peptized collagen and mixtures thereof are determined. Adsorption of MDP onto HAP can be described in terms of a modified Langmuir adsorption isotherm, in which each MDP molecule replaces or occupies two phosphate sites in the crystal surface. A model is presented relating adsorption constants determined from kinetic experiments to adsorption constants determined from equilibrium measurements. The model is based on the assumption that the rate-controlling process is a surface process involving a critical phenomenon such as surface nucleation. An expression for the kinetic effect on a crystal growth or dissolution surface process, due to adsorption of more than one inhibitor, is given. The concept of additivity of the effects of inhibitors is discussed.