X-ray Diffraction Analysis of the Reaction Products of Hydroxyapatite and Lanthanum

Abstract

As reported previously, the enamel surface of non-carious extracted human teeth were treated with 8% lanthanum nitrate solution (La solution), so that Ca²⁺ was displaced by La³⁺ in the enamel surface, and then the surface was coated with La³⁺.
The purpose of this study was to investigate the process of reaction and to discover its products.
After the synthetic hydroxyapatite (HAP) was treated with 0.01-8% La solution (pH 3.2-3.5) for 1-7 days, at regular intervals, the intake of La into HAP was analyzed by X-ray diffractometry.
The products of the lanthanum compounds were observed in HAP which was treated with 0.5-8% La solution, but this reaction did not appear in La solution of less than 0.1%.
This reaction was the displacement of Ca with La in HAP, which formed the lanthanum phosphate compounds LaPO₄ and La₄ (P₂O₇) ₃.
The quantity of La in HAP reached about 20-26% and the amount of Ca was decreased, but the movement of P was small.
The higher the density of the La solution was, the more Ca was dissolved and the lower the density was, the more P was dissolved.
Lanthanum phosphate compounds were produced in the enamel surface of extracted human teeth which were treated with 8% La solution. The compounds included LaPO₄, La₄ (P₂O₇) ₃, LaP₅O₁₄, LaHP₂O₇·3H₂O, and LaP₃O₉·3H₂O.