Solubility of TTCP and beta-TCP by solid titration
1Dental Materials Science, Faculty of Dentistry, The University of Hong Kong, Hong Kong.
Archives of Oral Biology
|May 6, 2009
Summary
Hydroxyapatite (HAp) is more stable than other calcium phosphates, even at lower pH levels. This finding contradicts previous research suggesting dicalcium phosphate dihydrate (DCPD) is more stable below pH 4.2.
Area of Science:
- Biomaterials Science
- Inorganic Chemistry
- Materials Science
Background:
- Calcium phosphates are crucial in biomaterials and bone chemistry.
- Previous studies suggested dicalcium phosphate dihydrate (DCPD) is more stable than other calcium phosphates below pH 4.2.
- The stability of tetracalcium phosphate (TTCP) and beta-tricalcium phosphate (beta-TCP) at varying pH levels requires further investigation.
Purpose of the Study:
- To determine the effective solubility and stability of TTCP and beta-TCP.
- To compare the stability of different calcium phosphates, including hydroxyapatite (HAp) and DCPD, across a range of pH values.
- To re-evaluate the widely accepted view on DCPD stability.
Main Methods:
- Solid titration was employed to assess the solubility of TTCP and beta-TCP in a 100 mM KCl solution at 37°C.
- pH levels ranged from approximately 2.9-9.2 for TTCP and 3-7.4 for beta-TCP.
- Precipitate characterization involved X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX).
Main Results:
- Hydroxyapatite (HAp) was the sole identified solid phase at equilibrium at pH 3.60 and 4.50.
- No residual titrant or other calcium phosphate phases were detected under these conditions.
- A significant change in the titration curve slope for TTCP was observed around pH 3.9.
Conclusions:
- Hydroxyapatite (HAp) demonstrates superior stability compared to other calcium phosphates, particularly at lower pH values.
- The study's findings contradict the established belief that DCPD is more stable than other calcium phosphates below pH 4.2.
- The results necessitate a revision of the understanding of calcium phosphate stability in physiological and biomaterial contexts.
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