Fluoride in plaque fluid and saliva after NaF or MFP rinses

Fluoride in Saliva and Oral Mucosa after Brushing with 1,450 or 5,000 ppm Fluoride Toothpaste

The aim was to measure and compare fluoride concentrations in oral mucosa and saliva following a single brushing with either 1,450 or 5,000 ppm fluoride toothpaste. Fourteen healthy participants provided saliva and oral mucosa samples in the morning before tooth brushing. Then participants brushed their teeth with 1,450 ppm fluoride toothpaste, and saliva and mucosa samples were collected after 1, 2, 4, and 6 h. The experiment was repeated 3-7 days later with 5,000 ppm fluoride toothpaste. All samples were analyzed for fluoride using an ion-selective electrode adapted for microanalysis. Pre-brushing fluoride concentrations were higher in mucosa (mean1,450 0.26 ppm and mean5,000 0.20 ppm) than in saliva (mean1,450 0.08 ppm and mean5,000 0.07 ppm). The mean fluoride concentrations increased in both mucosa and saliva following a single brushing with both 1,450 ppm (meanmuc1,450 (1 h) 1.15 ppm, meansal1,450 (1 h) 0.33 ppm) and 5,000 ppm fluoride toothpaste (meanmuc5,000 (1 h) 3.21 ppm and meansal5,000 (1 h) 0.90 ppm). At 6 h, the fluoride concentrations had returned to pre-brushing levels. Across the 6-h sampling period the fluoride concentration in saliva was statistically significantly 1.4 times higher following brushing with 5,000 ppm compared with 1,450 ppm fluoride toothpaste. For mucosa, this ratio was only 1.1 and not statistically significant. In conclusion, the fluoride level in oral buccal mucosa is higher than in saliva and follows the same fluoride clearance pattern as in saliva. Over the initial 6-h period following a single tooth brushing, the ratio of the fluoride concentration in mucosa to that in saliva is independent of the fluoride concentrations in the toothpastes used.

Fluoride in Dental Biofilm Varies across Intra-Oral Regions

Information on differences in biofilm fluoride concentration across intra-oral regions may help explain the distribution of caries within the dentition. The aim of this cross-sectional study was to describe the fluoride concentration in saliva and in biofilm fluid and biofilm solids across 6 intra-oral regions. Unstimulated whole saliva was collected from 42 participants and biofilm harvested from the buccal sites in the 4 molar and 2 anterior regions. Samples were collected at least 1 h after use of fluoride dentifrice. No attempt was made to control the participants' food consumption or use of other topical agents. Centrifuged saliva, biofilm fluid, and biofilm solids were analysed for fluoride using a fluoride ion-selective electrode, adapted for microanalysis. Fluoride in biofilm varied across intra-oral regions. The mean biofilm fluid fluoride concentrations across the oral cavity ranged from 11.6 to 16.8 µM, being statistically significantly higher in the upper anterior region than in any other region. In all regions the fluoride concentration in biofilm fluid was higher than in saliva. For biofilm solids the fluoride concentration was highest in the lower anterior region (2,461 μmol/kg) and lowest in the lower molar regions (388 and 406 μmol/kg, respectively). Within biofilm, the solids contained most of the fluoride (81 to >99%). The biofilm fluid fluoride concentration was significantly positively associated with salivary fluoride and only marginally associated with that of biofilm solids. In conclusion, this study has shown pronounced differences in fluoride distribution across intra-oral regions and compartments. This shows that the sampling site is a crucial factor for studies of biofilm fluoride.

Mechanistic Observations on the Role of the Stannous Ion in Caries Lesion De- and Remineralization

Two mechanistic, laboratory, factorial design studies were conducted to investigate the effect of the stannous ion (Sn2+) in the absence or presence of fluoride on caries lesion de- and remineralization. Study I was concerned with determining changes in mineral distribution of subsurface lesions, whereas study II investigated changes in surface hardness of surface-softened lesions as a function of pH. Study I showed that Sn2+ modulates the effects of fluoride by preventing lamination. Study II revealed that the effect of Sn2+ on rehardening is pH dependent. Neither study demonstrated synergy between Sn2+ and fluoride, yet interactions were observed. Sn2+ does interfere with remineralization to some extent although it provided acid resistance. The role of Sn2+ in the caries process is complex.

Salivary fluoride levels after use of high-fluoride dentifrice

The aim of the study was to evaluate salivary fluoride (F) availability after toothbrushing with a high-F dentifrice. Twelve adult volunteers took part in this crossover and blind study. F concentration in saliva was determined after brushing with a high-F dentifrice (5000 µg F/g) or with a conventional F concentration dentifrice (1100 µg F/g) followed by a 15 mL distilled water rinse. Samples of nonstimulated saliva were collected on the following times: before (baseline), and immediately after spit (time = 0) and after 1, 2, 3, 4, 5, 10, 15, 20, 30, 45, 60, 90, and 120 min. F analysis was performed with a fluoride-sensitive electrode and the area under curve of F salivary concentration × time (µg F/mL × min⁻¹) was calculated. At baseline, no significant difference was found among dentifrices (P > 0.05). After brushing, both dentifrices caused an elevated fluoride level in saliva; however salivary F concentration was significantly higher at all times, when high-F dentifrice was used (P < 0.01). Even after 120 min, salivary F concentration was still higher than the baseline values for both dentifrices (P < 0.001). High-F dentifrice enhanced the bioavailability of salivary F, being an option for caries management in patients with high caries risk.

Diet and the microbial aetiology of dental caries: new paradigms

The microbial and dietary factors that drive caries have been studied scientifically for 120 years. Frequent and/or excessive sugar (especially sucrose) consumption has been ascribed a central role in caries causation, while Streptococcus mutans appeared to play the key role in metabolising sucrose to produce lactic acid, which can demineralise enamel. Many authors described caries as a transmissible infectious disease. However, more recent data have shifted these paradigms. Streptococcus mutans does not fulfil Koch's postulates - presence of the organism leading to disease, and absence of the organism precluding disease. Furthermore, molecular microbiological methods have shown that, even with a sugar-rich diet, a much broader spectrum of acidogenic microbes is found in dental plaque. While simple sugars can be cariogenic, cooked starches are also now recognised to be a caries threat, especially because such starches, while not 'sticky in the hand', can be highly retentive in the mouth. Metabolism of starch particles can yield a prolonged acidic challenge, especially at retentive, caries-prone sites. These changes in the paradigms of caries aetiology have important implications for caries control strategies. Preventing the transmission of S. mutans will likely be inadequate to prevent caries if a sufficiently carbohydrate-rich diet continues. Similarly, restriction of sucrose intake, although welcome, would be unlikely to be a panacea for caries, especially if frequent starch intake persisted. Instead, approaches to optimise fluoride delivery, to target plaque acidogenicity or acidogenic microbes, to promote plaque alkali generation, to increase salivary flow or replace fermentable carbohydrates with non-fermentable alternatives may be more promising.

Enamel fluoride uptake from mouthrinse solutions with different NaF concentrations

OBJECTIVES

The influence on enamel fluoride uptake of reducing the NaF concentration of a mouthrinse solution by half, from 0.05-0.025%, was examined in elementary school children.

METHODS

The participatory elementary school had employed school-based fluoride mouthrinse with 0.05% NaF solution since 1983, and in 1993, the NaF content was lowered to 0.025%. Dental examination and enamel biopsy of maxillary central incisors were performed just before the NaF content reduction for children who had received the daily 0.05% NaF mouthrinse for 2-5 years since 6 years of age. During 1993-95, dental examination and enamel biopsy were undertaken for newly enrolled 6-year-old children, and the same subjects were re-examined after 2 years. The same series of examinations were conducted for the control group, which consisted of children belonging to another elementary school without a fluoride program.

RESULTS

The enamel fluoride concentration of 8-year-old children who used the 0.025% NaF mouthrinse for 2 years was 1810 +/- 535 ppm, reaching the same order as that in children who continued using the 0.05% NaF mouthrinse (1863 +/- 1358 ppm), and was significantly higher than that of children without fluoride programs (1113 +/- 303 ppm). There was no considerable increase of mean DMFT values due to the NaF content reduction.

CONCLUSIONS

It was concluded that a daily 0.025% NaF mouthrinse provides the similar fluoride content for enamel as 0.05% NaF mouthrinse as long as the rinsing frequency is maintained.

Effect in vitro acidification on plaque fluid composition with and without a NaF or a controlled-release fluoride rinse

Plaque fluid ion concentration changes, especially fluoride, in response to the pH decrease associated with a cariogenic episode are important components of the caries process. A "controlled-release" (CR) fluoride rinse, based on the controlled release of fluoride in the presence of calcium, has been shown to form large fluoride reservoirs in resting plaque. In this study, the in vitro acid-induced release of fluoride, and other ions, was examined in 48-hour-fasted plaque fluid from subjects (n = 11) who received no rinse, or who used a 228-ppm CR or NaF fluoride rinse 1 hr before being sampled. After collection, the plaque was centrifuged to yield plaque fluid, acidified (0.1 microL of 0.5 mol/L HCl per milligram plaque), and then re-centrifuged before a second sample was obtained. Although previous studies indicated a higher plaque fluid fluoride after the new rinse relative to NaF, no statistically significant difference was observed here. Average fluoride release after acidification (average pH, 5.2) was statistically greater following the use of the CR rinse (153 micromol/L) compared with the NaF rinse (17 micromol/L). No fluoride release was seen in the no-rinse samples. The pH, free calcium, phosphate, acetate, propionate, and buffer capacity were not affected by the different amounts of fluoride deposited in the plaque. However, following acid addition, an increase in free calcium and phosphate was observed, which was also independent of the rinse. The large release of fluoride following acidification suggests that the new rinse may provide an improved cariostatic effect.

Fluoride in the oral environment

A predominant part of the cariostatic activity of fluoride is a function of its concentration in the fluid environment of the teeth. The fluoride exposure results in a slightly elevated steady-state level of fluoride in the oral fluids, primarily in saliva and plaque fluid. So far, however, little is known about the intra-oral fluoride concentration necessary to achieve a cariostatic effect at the site of action. Following fluoride intake, the fluoride remaining in the oral cavity is diluted by the saliva pool. The remaining fluoride may be found in several compartments in the oral cavity. It may be ionized in saliva, ionized in plaque (plaque fluid), bound in plaque, bound as calcium fluoride, bound to enamel, and bound to soft tissues. Fluoride is also distributed to the oral tissues and into the dental plaque by diffusion. It is well established that plaque, after fluoride exposure, becomes a fluoride reservoir which stores for some time and releases fluoride. The present review gives an insight into the important parameters that determine the disposition and fate of fluoride in the oral environment. To achieve in-depth understanding, and hence formulation of the optimal fluoride therapy, more information is needed to consolidate our understanding of the distribution, retention, and elimination of fluoride in the oral cavity. Such knowledge will form a better basis for providing our patients with more effective dental fluoride products and regimens.