Inhibition of erosive dissolution by sodium fluoride: evidence for a dose-response.

OBJECTIVES: The aim of this study was to investigate the protective effects of sodium fluoride solutions and commercial mouthrinses on hydroxyapatite (HA) dissolution in citric acid in vitro, with and without a salivary pellicle. METHODS: A rapid-throughput HA solubility-reduction model was employed in which HA dissolution was quantified using ion chromatography. Two HA substrates were selected, a high-resolution powder and 80 µm diameter beads, and studied in the presence and absence of a salivary pellicle (pooled human saliva, 2 h). Immediately prior to acid exposure, substrates were exposed to one of a number of pre-treatments that included aqueous fluoride (F(-)) solutions and commercially available mouthrinses with F(-) concentrations of 0-450 µg/g (as NaF). Dissolution reduction was calculated relative to a deionised water negative control. RESULTS: For aqueous solutions and mouthrinses, a fluoride dose-response was observed with a plateau around 100 µg/g F(-) for both HA substrates, with or without pellicle. Concentrations as low as 10 µg/g F(-) significantly reduced HA dissolution. The HA substrate had little impact on the fluoride dose-response, and the fluoride was equally effective in the presence of a pellicle as in its absence. CONCLUSIONS: Fluoride significantly reduced HA dissolution at concentrations of 10 µg/g and higher. A fluoride dose-response was seen at low concentrations. This study illustrates the use of a powerful rapid-throughput HA solubility-reduction model for investigating HA dissolution in citric acid in the presence of dissolution inhibitors. CLINICAL SIGNIFICANCE: A single exposure to fluoride solutions with fluoride concentrations and exposure time representative of brushing or rinsing with mainstream oral care products was shown to significantly inhibit HA dissolution under conditions relevant to dental erosion. A similar efficacy was observed in the presence and absence of salivary pellicle.

Inhibition of dental erosion by casein and casein-derived proteins.

The application of milk-derived proteins such as casein as anti-erosion agents in oral healthcare products is of current interest. The aim of this study was to investigate the potential of 3 commercially available, milk-derived proteins as agents to inhibit enamel erosion. Aqueous solutions of 0.5% w/v casein, casein phosphopeptide (CPP) or glycomacropeptide (GMP) with and without 300 ppm fluoride (F, as NaF) were investigated with regard to enamel softening and tissue loss, in comparison with a deionised water (DIW) negative control and 300 ppm F positive control. Casein and F reduced enamel surface softening compared to DIW, but CPP and GMP did not (DIW: 58.2% reduction in hardness; F: 13.3%; casein: 21.8%; CPP: 50.8%; GMP: 62.4%). Similar results were obtained with solutions containing protein and F, and the effects were statistically indistinguishable from protein alone (casein + F: 19.1%; CPP + F: 48.2%; GMP + F: 66.1%). By contrast, all protein solutions and F significantly reduced tissue loss (p < 0.050; DIW: 25.8 µm tissue loss; F: 21.6 µm; casein: 20.3 µm; CPP: 20.5 µm; GMP: 20.0 µm). Solutions containing protein and F reduced erosion more than protein alone, but this difference was only significant from protein alone for casein (casein + F: 12.2 µm; CPP + F: 17.3 µm; GMP + F: 18.2 µm). Casein and casein-derived proteins may therefore have the potential to act as agents to reduce or prevent enamel erosion. Furthermore, the erosion-reducing efficacy is not reduced by F, and is in some cases enhanced.

Thermodynamic considerations of microgel swelling behavior.

A simple but novel thermodynamic model is presented, based upon van't Hoff analysis, for the reversible swelling behavior of colloidal microgels. The swelling, as a function of temperature, of poly(N-isopropylacrylamide/N,N'-methylenebisacrylamide) as well as poly(N-isopropylacrylamide/vinylpyridine/N,N'-methylenebisacrylamide) and poly(N-isopropylacrylamide/acrylic acid/N,N'-methylenebisacrylamide) microgel dispersions in H2O and D2O has been studied by photon correlation spectroscopy (PCS). PCS data was used to obtain the hydrodynamic diameter and hence the volume of the microgels (before and after reconstitution following freeze-drying) as a function of temperature. The choice of standard reference states, for analyzing the data attained, is discussed, and the one selected is that of the volume of the microgels at 333 K in H2O. For all microgels examined the volume, at this temperature, is shown to be independent of solvent (H2O, D2O). The derived data has allowed the exploration of a novel thermodynamic approach to the study of the swelling behavior of the microgels. The constant volume, at 333 K, for each of the polymer systems constituting the microgels is suggested to be an intrinsic property of the polymers themselves.