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Solubility of calcium fluoride and fluorapatite by solid titration
1Dental Materials Science, Faculty of Dentistry, The University of Hong Kong, Hong Kong, China.
Archives of Oral Biology
|April 25, 2007
Summary
This study determined the solubility of calcium fluoride (CaF2) and fluorapatite (FAp) using solid titration. Results show FAp is less soluble than hydroxyapatite (HAp), with implications for dental health and fluoride treatments.
Area of Science:
- Dental research
- Materials science
- Chemistry
Background:
- Topical fluoride treatments form calcium fluoride (CaF2) and fluorapatite (FAp) on teeth.
- Understanding the solubility of these compounds is crucial for preventing acid dissolution (caries).
- Solid titration is a reliable method for studying complex solubility systems.
Purpose of the Study:
- To determine the solubility isotherms of CaF2 and FAp.
- To compare the solubility of FAp with hydroxyapatite (HAp).
- To assess the reliability of the solid titration method in fluoride chemistry.
Main Methods:
- Solid titration was employed to measure CaF2 solubility (pH 2.3-9.5) and FAp solubility (pH 2.8-5.1).
- Experiments were conducted in 100mM KCl solution at 37°C.
- Apparent solubility of HAp in the presence of 1mM fluoride was also determined.
Main Results:
- Initial experiments were affected by fluoride interaction with glass; wax-lined apparatus resolved this.
- CaF2 solubility followed theoretical expectations below pH 8, with CaFOH postulated above this.
- FAp was found to be approximately 0.63 times less soluble than HAp.
- FAp was the sole equilibrium solid at pH 3.2, 3.6, and 4.1.
- 1mM fluoride slightly decreased HAp apparent solubility.
Conclusions:
- The solid titration method is reliable for fluoride systems once glass interferences are addressed.
- Fluoride's interaction with borosilicate glass may necessitate re-evaluation of previous studies.
- FAp solubility is comparable to HAp solubility determined by solid titration.
- Excess-solid method results for FAp solubility may be unreliable due to a lack of solution speciation data.
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