Degrees of saturation with respect to apatites in parotid saliva at various pH values

Abstract

The purpose of the present work was to investigate the degrees of saturation with respect to hydroxyapatite and fluorapatite in saliva at various pH's. The data of ionic activities in parotid saliva were collected from the literature and the degrees of saturation with respect to hydroxyapatite and fluorapatite were calculated. It was found that parotid saliva was supersaturated with respect to both apatites above pH 5.5, unsaturated with respect to hydroxyapatite and concurrently supersaturated with respect to fluorapatite in the pli range 5.5-4.5, while it was unsaturated with respect to both apatites below pH 4.5. In the laboratory it has been found that when enamel is exposed to a liquid unsaturated with respect to hydroxyapatite and supersaturated with respect to fluorapatite, a caries-like lesion is developed. A liquid unsaturated with respect to both apatites leads to an erosion-like injury. It is concluded that the two chemical conditions leading to the two types of enamel lesions may both occur in the oral cavity.In previous studies, it has been shown that calcium, phosphate and fluoride sufficient enamel can be dissolved in two fundament-to supersaturate the oral fluids with respect ally different ways: when the liquid phase to the enamel mineral at physiologic pH is unsaturated with respect to both hyd-(BENEDICT & KANTHAK 1932, SCHMIDTroxyapatite and fluorapatite, both apatites NIELSEN 1946, ERICSSON 1949 dissolve coincidently, which results in an 1968a). Furthermore, it has been demonerosion-like surface etching. The other strated that saliva becomes less supersatutype of dissolution is caused by a liquid rated and even unsaturated with respect which is unsaturated with respect to hyd-to enamel when pH decreases, owing to roxyapatite and supersaturated with re-the increase-of the enamel solubility spect to fluorapatite, which causes a for- (SCHMIDT-NIELSEN 1946, ERICSSON 1949. mation of fluorapatite and a dissolution of However, how the degrees of saturation hydroxyapatite, the resulting lesion being with respect to hydroxyapatite and fluorvery like a natural caries lesion in vivo apatite in saliva change as a function of (LARSEN 1974a,b). pH has not yet been investigated. It has been shown that saliva contains Therefore, based on data collected from

Plaque Fluoride Concentrations in a Community without Water Fluoridation: Effects of Calcium and Use of a Fluoride or Placebo Dentifrice

“…The explanation for this is not clear. While there is evidence that enamel contributes to plaque calcium concen-trations upon exposure to sucrose [Rankine et al, 1996;Tanaka and Margolis, 1999], saliva is probably the major source of the calcium acquired by plaque since it is supersaturated with several calcium salts [Larsen, 1975;Carey et al, 1986;Pearce, 1991;Shellis and Duckworth, 1994;Larsen and Pearce, 2003]. However, while plaque calcium concentrations vary widely, salivary calcium concentrations fall within a narrow range (table 1).…”

Plaque Fluoride Concentrations Are Dependent on Plaque Calcium Concentrations

“…The quantitative aspects of the distribution of calcium in plaque are not known, but it is known that it exists in several compartments. As in saliva, plaque fluid has been reported to be supersaturated with respect to several calcium salts including brushite, hydroxyapatite, calcium fluoride and amorphous calcium phosphate [Kaufman and Kleinberg, 1973;Larsen, 1975;Carey et al, 1986;Pearce, 1991;Shellis and Duckworth, 1994]. These salts are located mainly in the extracellular fluid spaces of plaque and each has the ability to form ionic bonds with fluoride, although with different affinities.…”

Effects of Flow Rate and pH on Calcium Phosphate Saturation in Human Parotid Saliva

“…The influ ence of pH on the degree of saturation with respect to HAP has been calculated for different flow rates by Larsen [1975], using the data of McCann [1968]. He found parotid saliva to be supersaturated with respect to HAP above pH 5.5.…”

“…The same approach was used by Larsen [1975], who investigated the influence of pH on the degree of saturation. There is, however, a lack of experimental data con cerning the influence of salivary flow rate and pH on the degree of saturation with respect to the calcium phosphates.…”