The Effect of pH on the Interaction of Fluoride and Salivary Ions

Abstract

The interaction between fluoride and some plaque components has indicated that fluoride binds to norganic salivary substances which are ultrafiltrable. The ffect of pH on the affinity of fluoride to these salivary sub stances was investigated in whole saliva, ultrafiltrated saliva, and ‘synthetic saliva’. When the pH was maintained above 7, an initial fluoride ion concentration of 10^-5m (0.2 ppm) decreased to 10^-6M (0.02 ppm). Addition of sucrose to incubated whole saliva or of hydrochloric acid to the inorganic solution prevented the decrease in fluoride ion concentration. In the absence of substances which decreased pH, the fluoride ion concentration decreased from the initial 10^-5M to 10^-6M. This bound fluoride was released when the pH was decreased by means of sucrose or acid. Upon storage of the ‘synthetic saliva’, the calcium concentration decreased from 2 × 10^-3M to 2 × 10^-4M. Fluoride per se seemed to have no measurable effect upon this decrease in calcium concentration. The decrease in fluoride and calcium concentrations was inhibited by citrate. These observations indicate that fluoride in plaque may be bound to a calcium phosphate precipitate, and that the binding is affected by the pH.

Therapeutic Modifications to the Mineral Ion Composition of Dental Plaque

“…A similar strong association was found in untreated plaque in this study, not only with respect to calcium and phosphate concentrations but also with respect to calcium and fluo ride concentrations, suggesting that some fluoride in normal plaque is bound to mineral. Some workers believe that fluo ride uptake is not related to calcium or phosphate uptake [Jenkins el al., 1969;Ed gar, 1973] while others consider that an as sociation is likely [Gron et al, 1969;Birkeland, 1973]. More recently Edgar [1981] has proposed a 2-stage process in which fluoride may first be taken up as part of a calcium phosphate complex and secon darily by plaque organisms.…”

Effect of Topical Fluoride Treatments on Fluoride Distribution during in vitro Caries-Like Lesion Formation

“…(8%) SnF2 treatment or no treatment. Each treatment group con taining 36 sections was further subdivided into groups of 12 sec tions and received either a 24-hour wash with 1.0 M KOH [Caslavska et al, 1975], an inorganic wash [Birkeland, 1973], or a 2-min distilled water rinse [Lovelock, 1973]. The inorganic rinse is com posed of NaHCOi (20 m Af), NaH2P 04 (3 m M), and CaCl2 (1 mM) in deionized water to emulate the inorganic constituents occurring naturally in human saliva.…”

In vitro Study on the Mechanisms of Action of Fluoride in Low Concentrations

“…Quantitative analyses of the solutions were carried out at intervals during the experimental period which generally was 36 h at 25 °C. The fluoride ion concentration, the pH, and the calcium content of the solutions were determined as previously described [Birkeland, 1973]. The risk of interference of phosphate in the calcium analyses was eliminated by adding lanthanum chloride to the solutions.…”

“…The clinical importance of these findings, however, remains to be established [Ericsson, 1968]. In addition, at least part of the fluoride in plaque seems to be bound by cations at a neutral pH [Birkeland and Rolla, 1972;Edgar and Jenkins, 1972;Birkeland, 1973], At pH 5, however, free fluoride ions may be present in the plaque [Birkeland, 1973[Birkeland, , 1974, The fluoride ions in the saliva-plaque-enamel interface are considered to have a cariostatic action [e.g., Hardwick, 1963;Jenkins, 1967; von der Fehr, 1970;Birkeland, 1973], either by resisting a decrease in pH [Jenkins et al, 1969] and/or by inducing formation of …”