The solubility of fluorapatite and its relationship to that of calcium fluoride

doi:10.1016/0003-9969(68)90014-9

Archives of Oral Biology

Volume 13, Issue 8, August 1968, Pages 987-1001

https://doi.org/10.1016/0003-9969(68)90014-9 Get rights and content

Abstract

The activity solubility product of calcium fluoride, K_s⁰ was found to be 3.58 ± 0.18 × 10⁻¹¹ (pK_s⁰ = 10.45) at 34 ° and the K_s⁰ of fluorapatite (FA) 8.6 ± 1.3 × 10⁻⁶¹ at 34 °. The pK_s⁰ of FA was 59.6 at 25 °C, 60.07 at 34 °, and 60.3 at 45 °. At 37 ° the calculated pK_s⁰ was 60.15. The K_s⁰ of FA was not significantly affected by variation of crystal size, solid to solution ratios, or ionic strength, and was constant from pH 4.5 to 6.4. Below pH 4.5 sufficient calcium and fluoride dissolved from FA to exceed the K_s⁰ of CaF₂, although solutions tended to remain in equilibrium with FA. Tables of solubility (mg/l) are given for FA and CaF₂ at pH 4–7.5 showing the influence of ionic strength, and added F, P, and Ca. The solubility of CaF₂ was shown to be 12–15 mg/l in saliva, whereas FA was essentially insoluble. It is concluded that the mechanism of action of F in caries inhibition is related to this stability of FA.

Résumé

Le produit activité solubilité du fluorure de calcium, K_s⁰ est de 3,58 ± 0,18 × 10⁻¹¹ (pK_s⁰ = 10,45) à 34 ° et le K_s⁰ du fluorapatite (FA) 8,6 ± 1,3 × 10⁻⁶¹ à 34 °. Le pK_s⁰ du FA est de 59,6 à 25 ° C, 60,07 à 34 ° et 60,3 à 45 °. A 37 °, le pK_s⁰ calculé est de 60,15. Le K_s⁰ du FA n'est pas modifié de façon significative par des variations de taille cristalline, par des rapports solide sur solution et par la force ionique. Il est constant de pH 4,5 à 6,4. Au-dessous de pH 4,5, une quantité suffisante de calcium et de fluorure se dissout à partir du FA pour être supérieure au K_s⁰ de CaF₂, bien que les solutions aient tendance à rester en équilibre avec FA. Des valeurs de solubilité (mg. par litre) sont déterminées pour FA et CaF₂ à pH 4 à 7,5 démontrant l'importance de la force ionique et de l'adjonction de F, P et Ca. La solubilité de CaF₂ est de 12–15 mg par litre de salive, alors que FA est pratiquement insoluble. Il semble que le mécanisme d'action de l'inhibition carieuse du F soit lié à cette stabilité du FA.

Zusammenfassung

Das Aktivitäts-Löslichkeitsprodukt von Kalziumfluorid K_s⁰ betrug 3,58 ± 0,18 × 10⁻¹¹ (pK_s⁰ = 10,45) bei 34 °, das K_s⁰ von Fluorapatit (FA) 8,6 ± 1,3 × 10⁻⁶¹ bei 34°. Das pK_s⁰ von FA betrug 59,6 bei 25 °C, 60,07 bei 34 ° und 60,3 bei 45 °. Für 37 ° beträgt das berechnete pK₁ 60,15. Das K_s⁰ von FA wurde durch Variation der Kristallgröβe, des Verhältnisses fester zu flüssiger Phasen oder der Ionenkonzentration nicht signifikant beeinflust und war von pH 4,5 bis 6,4 konstant. Unter pH 4,5 löste sich aus FA genügend Kalzium und Fluorid, um das K_s⁰ von CaF₂zu übertreffen, obwohl die Lösungen dazu neigten, im Gleichgewicht mit FA zu bleiben. Es werden für FA und CaF₂ Löslichkeitstabellen (mg pro Liter) von pH 4 bis 7,5 angegeben, welche den Einfluβ der Ionenkonzentration und zugefügten F, P und Ca zeigen. Die Löslichkeit von CaF₂ wurde im Speichel mit 12–15 mg/l nachgewiesen, während FA völlig unlöslich war. Es wird der Schluβ gezogen, daβ der Mechanismus der Fluorwirkung bei der Karieshemmung mit dieser Stabilität des FA zusammenhängt.

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The solubility of fluorapatite and its relationship to that of calcium fluoride

Abstract

Résumé

Zusammenfassung

Archs oral Biol.

J. biol. Chem.

Archs oral Biol.

Archs oral. Biol.

J. biol. Chem.

Archs oral Biol.

First dissociation constant of phosphoric acid from 0 ° to 60 °; limitations of the electromotive force method for moderately strong acids

J. Res. natn. Bur. Stand.

pH values of certain phosphate-chlorine mixtures and the second dissociation constant of phosphoric acid from 0 ° to 60 °

J. Res. natn. Bur. Stand.

K. danske Vidensk. Selsk., Math-fys. Medd.

Thermodynamics of aqueous HF solutions

J. Am. chem. Soc.

The chemistry of caries inhibition—problems and challenges in topical treatments

J. dent. Res.

Dissociation constants of the alkaline-earth salts of some monocarboxylic acids

J. chem. Soc.

Complexing of magnesium ion by fluoride ion

J. Am. chem. Soc.

System CaOP2O5HFH2O: thermodynamic properties

J. phys. Chem.

Solubility behavior of dental enamel and other calcium phosphates

Ann. N. Y. Acad. Sci.

Determination of phosphate by differential spectrophotometry

Analyt. Chem.

System CaOP₂O₅HFH₂O: thermodynamic properties