Chemical Stability of Carbonate- and Fluoride-Containing Apatites

Abstract

Apatites containing CO₃ and/or F were synthesized and exposed to acid buffer. The extent of dissolution was determined (as mMCa/ml buffer solution) and the apatites characterized by X-ray diffraction, IR absorption, and chemical analyses before and after acid exposure. Results showed that: (i) the extent of dissolution was directly proportional to the CO₃ contents but that the simultaneous presence of F in the apatite minimized the adverse CO₃ effect; (ii) the extent of dissolution during the second exposure was much less than during the first exposure; (iii) the lattice parameters, crystal-Unity and CO₃ and F contents of the apatites differed before and after exposure to the acid buffer, i.e., larger a-axis, initial decrease then increase in crystallinity, lower carbonate and higher fluoride contents of apatites after acid exposure. Results from this study suggest that the vulnerability of synthetic and biological apatites to acid dissolution is largely due to their carbonate constituent and that the caries process may involve a combination of dissolution of carbonate-rich/fluoride-poor apatites and reprecipitation of carbonate-poor/fluoride-rich enamel apatites and that the reprecipitated apatite is rendered more resistant to acid dissolution.

In vitro degradation of calcium phosphates: Effect of multiscale porosity, textural properties and composition

“…Interestingly, despite the comparable values in SSA between carbonated doped HA (C-CDHA C ) and the non-carbonated substrates (CDHA C , CDHA F ), the degradation behaviour was significantly lower for the carbonated samples (p<0.05). This was unexpected, since the incorporation of carbonate ions in the hydroxyapatite lattice is known to markedly disturb the crystal lattice [52] increasing its solubility [53][54][55]. Quantitatively, C-CDHA C resorption was reduced by a 30-50 % compared to CDHA F , regardless of the L/P ratio.…”

Organic–Inorganic Surface Modifications for Titanium Implant Surfaces

“…The relation between carbonate apatite and hydroxyapatite is important, because carbonate increases the chemical reactivity of apatites. This occurs by an increase of the solubility of the product and rate of dissolution in acids, and by reducing the thermal stability (34). Since carbonate is known as an effective crystal growth inhibitor, carbonate apatite consists of smaller crystals than hydroxyapatite (7).…”

High-resolution X-ray microdiffraction analysis of natural teeth

“…The carbonate-apatite was thought to be relevant to the early stages of dental decay, as it was apparent that carbonate inclusion in apatite markedly changed its properties and increased its solubility. Fluorapatite is the most stable among the dental apatites, and has less solubility and more acid resistance than hydroxyapatite (LeGeros et al, 1996;Mathew & Takagi, 2001;LeGeros & Ming, 1983;Ten Cate, 1997;Legeros, 1991;Gruner et al, 1937).…”