Zinc effect on the in vitro formation of calcium phosphates: Relevance to clinical inhibition of calculus formation

Purpose: To determine the effect of zinc on the in vitro formation of calci um phosphates and its relevance to calculus inhibition. Materials and Metho ds: Different types of calcium phosphate phases (amorphous calcium phosphat e, ACP; dicalcium phosphate dihydrate, DCPD; octacalcium phosphate, OCP; an d carbonate hydoxyapatite, CHA) were precipitated from solutions containing increasing concentrations of zinc (Zn) ions. The precipitates were charact erized using x-ray diffraction, infrared absorption spectroscopy, and scann ing electron microscopy. Results: The presence of Zn ions affected the type and amount of calcium phosphate phases formed. Zn, even at concentrations as law as 0.1 mM/L, inhibited the crystal growth of DCPD, OCP and AP; and, at higher concentrations (0.5 mM to 2 mM/L), promoted the formation of amor phous calcium phosphate, ACP, or Zn-substituted tricalcium phosphate (beta- TCP) depending on the reaction pH and temperature.