The direct determination of fluoride in human saliva by a fluoride electrode. Fluoride levels in parotid saliva after ingestion of single doses of sodium fluoride

Recognition of fluoride anions at low ppm level inside living cells and from fluorosis affected tooth and saliva samples

A simple Schiff base chemosensor 2-((2-(2,4-dinitro phenyl)hydrazono)methyl)-4-nitrophenol (L) has been developed as a colorimetric and fluorimetric ‘turn on’ sensor for fluoride (F⁻).

Saliva fluoride before and during 3 years of supervised use of fluoride toothpaste

OBJECTIVES

The purpose of the study was to examine pre-brushing saliva fluoride concentrations before and during a large, 3-year, prospective toothpaste study on the effect of post-brushing rinsing on dental caries. The aims were to study saliva fluoride over time and the effect of rinsing on saliva fluoride and to relate saliva fluoride to caries increments and accumulation of plaque.

MATERIALS AND METHODS

Saliva samples (baseline and 1, 2, and 3 years) were collected from 11-year-old children attending two schools (A and B) in Kaunas, Lithuania, who refrained from brushing the evening and morning before saliva collection. Numbers of saliva samples collected varied from 264 at baseline to 188 at the 3-year follow-up. Children in school A rinsed with water after daily brushing, while children in school B did not rinse. Total caries and visible plaque were registered at baseline and after 3 years.

RESULTS

Mean saliva fluoride concentrations at baseline and after 1, 2, and 3 years from school A (rinsing) were 0.014, 0.026, 0.029, and 0.034 ppm and from school B (no rinsing) were 0.013, 0.028, 0.031, and 0.031 ppm, respectively. Increases in saliva fluoride from baseline were significant (Wilcoxon's test, p < 0.001), but the increase from baseline to year 1 was not statistically significantly different between schools. Saliva fluoride did not increase beyond year 1 and did at no time point differ between schools. Reductions in numbers of tooth surfaces with dental plaque were significantly positively related to the number of caries reversals over the 3 years.

CONCLUSIONS

Background saliva fluoride concentration is increased by brushing at least once daily on schooldays, does not increase further over 3 years, and is not affected by rinsing after brushing.

CLINICAL RELEVANCE

Continuous use of fluoride toothpaste produces ambient saliva fluoride levels similar to saliva fluoride in areas with fluoridated water.

Influência de diferentes concentrações de flúor na água em indicadores epidemiológicos de saúde/doença bucal

O objetivo deste estudo foi avaliar o acesso a fontes de fluoreto e as condições de saúde bucal de 237 escolares de nove a dezesseis anos, de três localidades com diferentes concentrações de fluoreto na água. O teor de flúor na água de cada região foi analisado pela técnica do eletrodo seletivo para o íon flúor e a foi avaliada prevalência de cárie e fluorose, respectivamente, pelo índice CPOD e TSIF, apresentando diferença estatisticamente significante (ANOVA; p < 0,05) nas três localidades: área sem fluoretação artificial (CPOD 5,32 ± 3,49) e 16% de fluorose; área com fluoretação artificial de 0,8 ppmF (CPOD 1,88 ± 2,22) e 94% de fluorose; área com fluoretação natural de 2,54 ppmF (CPOD 3,96 ± 2,38) e 100% de fluorose. Os achados sugerem que os indicadores epidemiológicos de saúde/doença bucal estudados são influenciados pela presença de fluoreto na água de consumo e que a supervisão e a orientação são fundamentais na correta utilização dos compostos fluoretados, aproveitando-se o máximo benefício no controle da cárie dentária com o mínimo risco de ocorrência de fluorose.

Development of gold standard ion-selective electrode-based methods for fluoride analysis

BACKGROUND/AIMS

Currently available techniques for fluoride analysis are not standardized. Therefore, this study was designed to develop standardized methods for analyzing fluoride in biological and nonbiological samples used for dental research.

METHODS

A group of nine laboratories analyzed a set of standardized samples for fluoride concentration using their own methods. The group then reviewed existing analytical techniques for fluoride analysis, identified inconsistencies in the use of these techniques and conducted testing to resolve differences. Based on the results of the testing undertaken to define the best approaches for the analysis, the group developed recommendations for direct and microdiffusion methods using the fluoride ion-selective electrode.

RESULTS

Initial results demonstrated that there was no consensus regarding the choice of analytical techniques for different types of samples. Although for several types of samples, the results of the fluoride analyses were similar among some laboratories, greater differences were observed for saliva, food and beverage samples. In spite of these initial differences, precise and true values of fluoride concentration, as well as smaller differences between laboratories, were obtained once the standardized methodologies were used. Intraclass correlation coefficients ranged from 0.90 to 0.93, for the analysis of a certified reference material, using the standardized methodologies.

CONCLUSION

The results of this study demonstrate that the development and use of standardized protocols for F analysis significantly decreased differences among laboratories and resulted in more precise and true values.

Fluoride uptake in dental enamel after using fluoridated dentifrice, preceded or not by a CaCl2 solution rinse

INTRODUCTION: The use of a calcium solution previously to brushing could favor the remineralization and the fluoride (F) uptake in dental enamel. OBJECTIVE: This study evaluated the F in dental enamel after using a F dentifrice, preceded or not by a rinse with a CaCl2 solution. METHODS: Ten subjects (18-30 years) participated in a double-blind, cross-over protocol. Enamel biopsy and 3 min saliva samples were obtained at baseline and after brushing (1.5 g Crest®, 1,000 ppm F as NaF), preceded by a rinse with 10 mL of 20 mM CaCl2 50 mM acetate pH 7.2 or deionized water, for 1 min, followed by a 15 mL water rinse for 5 sec. Biopsies were made before the rinses and after 8-15 and 120 min. Saliva samples were collected before the rinses and after 4, 15, 30, 60 and 120 min. F concentration in enamel biopsies was analyzed with the F electrode (Orion 9409) and a miniature calomel reference electrode, while phosphorus concentration was analyzed by spectrophotometry. Saliva samples were analyzed for F with the electrode (Orion 9609) by the direct method. The data were analyzed by ANOVA and Tukey test (p<0.05). RESULTS: Mean F concentration ± SD (µg/mL) at baseline up to 120 min for saliva samples were: 0.02±0.01; 9.06±4.26; 2.01±1.76; 0.47±0.33; 0.24±0.17; 0.08±0.08; 0.07±0.04 for the deionized water rinse, and 0.02±0.02; 10.96±14.21; 2.76±3.04; 0.87±1.29; 0.40±0.66; 0.16±0.23; 0.09±0.09 for the CaCl2 rinse. The data for enamel biopsies were (µg/g): 1861.7±1011.0; 1790.5±953.2; 1117.6±585.2 for the deionized water rinse, and 1586.4±776.8; 1536.3±546.4; 1520.5±1340.7 for the CaCl2 rinse. CONCLUSION: According to this protocol, there was not a significant variation in enamel F uptake after using a F dentifrice preceded or not by a rinse with a CaCl2 solution.

Fluoride concentrations in plaque, whole saliva, and ductal saliva after application of home-use topical fluorides [published eerratum appears in J Dent Res 1993 Jan;72(1):87]

It is now well-accepted that the primary anti-caries activity of fluoride (F) is via topical action. The retention of F in the mouth after topical fluoride treatment is considered to be an important factor in the clinical efficacy of F. The purpose of this study was to evaluate F levels in ductal saliva, whole saliva, and pooled plaque after treatment with topical F agents intended for home use. Ten consenting adults, mean (SD) age 31.0 (8.2) years, participated in all aspects of the study. Two days before each test, subjects received a professional tooth cleaning and subsequently abstained from all oral hygiene procedures to permit plaque to accumulate, and from the use of F-containing dental products. Treatments consisted of a placebo dentifrice (PD), fluoride dentifrice (FD; 0.24% NaF), fluoride rinse (FR; 0.05% NaF), and fluoride gel (FG; 1.1% NaF). Unstimulated whole saliva and pooled plaque were sampled at multiple points over a 24-hour period. In a separate experimental series, stimulated parotid saliva was sampled over a two-hour period after treatment. Fluoride levels generally followed the same pattern in whole saliva and pooled plaque samples, with FG > FR > FD > PD. Night-time F application resulted in prolonged F retention in whole saliva but not in plaque. Fluoride levels in parotid saliva were only slightly higher after F treatment and returned to baseline levels within two h. The results of this study indicate that the method of F delivery, the F concentration of the agent, and the time of application (daytime vs. night-time) are important factors influencing F levels in the mouth.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies of fluoride retention by oral soft tissues after the application of home-use topical fluorides

Previous studies have focused on enamel and plaque as the primary sites of fluoride (F) retention in the mouth. The present study was undertaken to evaluate the role of oral soft tissue as a site of F retention by comparing an edentulous subject panel (n = 9) with a fully dentate panel (n = 10). Unstimulated whole saliva samples were collected by having subjects pool saliva for two min. Samples were collected over a 24-hour period after application of a placebo dentifrice (PD; 0.4 ppm F), fluoride dentifrice (FD; 1100 ppm F), fluoride rinse (FR; 226 ppm F), or fluoride gel (FG; 5000 ppm F) delivered in custom trays. There was no statistically significant difference in salivary flow rate between the two panels for any of the treatments. The edentulous panel had higher salivary F levels than the dentate panel, which reached statistical significance (p less than 0.05) for the FD and FG treatments. In a separate study involving the same treatments, F levels at specific soft-tissue sites were measured over a one-hour period by use of absorbent discs placed in different soft-tissue areas of the mouth. The tongue and lower posterior vestibule retained the highest F levels, followed by the upper posterior buccal vestibule and upper anterior labial vestibule, with the lowest F levels retained in the lower anterior vestibule and the floor of the mouth. There was a strong-to-moderate correlation between whole saliva F concentration and F levels at specific soft-tissue sites. This study establishes the importance of oral soft tissue as the major site of F retention in the mouth.

A study of the relationship between trace elements in saliva and dental caries in children

About 8 ml of saliva were collected from each of 272 children, living in rural areas in North India, equally distributed into age groups 4-7 and 12-16 yr and stratified into low, moderate and high caries groups. The salivas were analysed for Zn, Cu, Fe, Mn by atomic absorption spectrophotometry and for F with a fluoride-sensitive electrode. The elements Cu and F had a consistent, inverse relationship with caries experience. The concentration of Zn, Fe and Mn in saliva did not have any consistent relationship with caries experience.

Kinetics of fluoride in the oral fluids

The normal concentration of fluoride in saliva is about 1 mumol/L, which is somewhat less than that in plasma, and the salivary concentration is relatively independent of flow rate. Even this low concentration appears to be significant in terms of maintaining the integrity of tooth mineral. After fluoride consumption, the level in plasma peaks within less than an hour, and this produces a corresponding increase in salivary levels, which achieve baseline values usually within a few hours. At low concentrations (less than 4 mmol/L) in oral fluids, fluoride undergoes only slight reaction with tooth mineral to form fluorohydroxyapatite. However, at higher concentrations calcium fluoride is formed on the tooth surface. Although this mineral is sparingly soluble in saliva, the process of dissolution is retarded for periods of up to a week or longer by surface deposition of salivary phosphate and pyrophosphate. The rate of clearance of exogenous fluoride from saliva is prolonged when initial concentrations are high, due to the deposition of CaF2 on the tooth surface and its gradual dissolution. The clearance rate is also not constant throughout the mouth, but shows considerable site-specificity. In general, clearance is much more rapid lingually than buccally. This appears to be due to the greater lingual exposure to secretions from the major salivary glands, principally the submandibular, whereas buccally, mainly minor mucous gland secretions are present, and these are very viscous and flow at a slow rate.

The rapid measurement of fluoride concentrations in stored human saliva by means of a differential electrode cell

For the purpose of rapid measurement, the performance of a differential cell, consisting of a combination pH electrode and a F- electrode and used at low pH (1.2), was compared with the use of a single F- electrode at pH 5.0. The differential cell proved to be as accurate and consistent as the single electrode: its response time was 2 min for a saliva volume of 50 microliters; the response time of the single electrode was 20 min with a saliva volume of 1000 microliters. Analysis of salivary supernatant fluid provided an unreliable guide to the original salivary F- concentrations but if fresh whole saliva was acidified to pH 1.2 immediately upon collection, the original baseline values were repeatedly obtained when measurements were made at intervals over a storage period of 14 days at 4 degrees C. Immediate acidification thus provides a satisfactory method for collecting samples from separate populations and then transporting them at leisure to a laboratory for direct measurement at pH 1.2 with the differential cell.

Comparison of fluoride concentrations in unstimulated whole saliva following the use of a fluoride dentifrice and a fluoride rinse

Recent evidence has suggested that the cariostatic effects of topical fluoride (F) are related to the presence of low concentrations of ionic F in the oral environment. The purpose of this study was to compare the retention of F in the oral environment over 24-hour periods after the use of a F dentifrice or a F rinse. Groups of ten consenting adult subjects (age 18-52 years) brushed and/or rinsed (B/R) in a standardized manner twice per day in the morning (AM) and before bed (PM) with either a placebo dentifrice (8 ppm F), NaF dentifrice (1100 ppm F), or NaF rinse (225 ppm F). Experiments were performed with placebo dentifrice only (PD); F dentifrice only (FD); F dentifrice followed by F rinse (FD/FR); placebo dentifrice followed by F rinse (PD/FR); and F rinse followed by placebo dentifrice (FR/PD). Unstimulated whole saliva samples were collected at baseline and then at 0, 15, 30, and 45 min, 1, 2, and 8 hr after B/R in the AM, after B/R in the PM and upon rising the following morning. Salivary flow rate and F were determined for each sampling interval. The results of this study suggest that: (1) F rinse may be a more effective way of delivering topical F than F dentifrice; (2) based on F retention, the combination of FD/FR was not more effective than FR only (PD/FR); (3) older individuals with gingival recession retained higher F levels; and (4) bedtime F application resulted in longer F retention than did daytime application, which may have important implications for enamel remineralization.

An experimental study of bio-availability of fluoride from dietary sources in man

After single, oral doses, 8 h profiles of fluoride (F) concentrations in plasma and saliva, and 24 h urinary excretions were determined in healthy adult volunteers. Bio-availability of F from dietary sources was evaluated in relation to that of NaF. Between 2 and 10 mg of F administered all 3 variables were dose-dependent. However, digestion, the chemical state of F, and interaction with accompanying foods may modify the kinetics of F passage through the human body. Low bio-availabilities were observed for most solid foods such as fish and algal flour and for mammalian and fish bones, when used as typical components of fluoride-rich foods such as meat- and fish-products. This data is important in the determination of optimum levels of F supplementation in human nutrition for caries-prevention programmes.

Binding of 18F by cell membranes and cell walls of Streptococcus mutans

The binding of 18F to isolated cell membranes and cell walls of Streptococcus mutans GS-5 or other bacteria was assayed. The attachment of 18F to these cell envelopes proceeded slowly and reached equilibrium within 60 min. 18F binding was stimulated by Ca2+ (1 mM). The binding of 18F to cellular components was dependent upon the pH, as well as the amount of 18F and dose of the binder employed. The binding of 18F by cell walls prepared from fluoride-sensitive and fluoride-resistant cells of S. salivarius and S. mutans did not differ significantly. The pretreatment of cell walls or cell membranes for 60 min at 30 degrees C with 1 mg of RNase, DNase, or trypsin per ml did not influence the binding of 18F by the walls and membranes of S. mutans GS-5. However, prior exposure of cell membranes to sodium dodecyl sulfate caused a significant reduction in the number of 18F atoms bound by the membranes. In saturated assay systems, cell membranes of S. mutans GS-5 bound 10(15) to 10(16) atoms of 18F per mg (dry weight), whereas cell walls from S. mutans GS-5, FA-1, and HS-6 or Actinomyces viscosus T14V and T14AV bound 10(12) to 10(13) atoms of 18F per mg (dry weight). 18F in this quantity (10(12) to 10(13) atoms) cannot be detected with the fluoride electrode. The data provide, for the first time, a demonstration of 18F binding by cell membranes and walls of oral flora.

Effect of continuous fluoride gel use on plaque fluoride retention and microbial activity

Twelve consecutive wk of daily five-minute topical applications of 1% NaF gel by non-cancer control subjects did not significantly affect plaque concentrations of Streptococcus mutans or Lactobacillus spp. Plaque F- levels increased 150% (P less than .001), while production of acetate and lactate decreased 40% (P less than .007) and 66% (P less than .001), respectively. Long-term (12 wk to more than five yr) fluoride gel use by post-irradiation xerostomic cancer patients was associated with increases in plaque F- and decreases in acidogenesis similar to those observed in the control subjects. Plaque concentrations of cariogenic organisms increased during the first yr of radiation-induced xerostomia and fluoride gel use, before starting to decline. Although sustained fluoride treatment increased (P less than .001) the ratio of fluoride-resistant to fluoride-sensitive strains, the number of patients harboring detectable S. mutans was diminished (P less than .001).

Clinical evaluation of an intraoral device for the controlled release of fluoride

An intraoral-releasing device designed to release 0.5 mg of fluoride per day was evaluated in a one-month trial. The results showed that the 11 men who wore the fluoride-releasing device on their maxillary first molars had significantly elevated levels of fluoride in their saliva and plaque compared with baseline levels. No significant changes were observed in mean serum or urine fluoride levels or in the gingival or plaque indexes during the study. The prevalence of S mutans in whole saliva did not change during the study and the relative proportion of S. mutans, S. sanguis, and A viscosus and A naeslundii in plaque also remained relatively stable. The elevated fluoride levels in saliva and plaque are presumptive evidence that the intraoral fluoride-releasing device could exert a cariostatic effect in humans. However, long-term clinical trials are needed to determine the cariostatic potential of this fluoride releasing system.

Fluoride in mixed human saliva after different topical fluoride treatments and possible relation to caries inhibition

Fluoride concentrations in mixed saliva were measured at different intervals following topical treatments with various fluoride preparations and procedures such as dentifrice, tablets, mouthrinse and topical solution. The results were related to available caries reduction data from corresponding clinical trials previously published. Salivary fluoride levels varied widely reflecting the different dosages applied, whereas the caries reduction data irrespective of type of treatment appear very similar, with a magnitude of about 30%. When combining salivary fluoride data with recent understanding of enamel-fluoride kinetics it was possible to explain the clinical caries reductions.

Fluoride levels in human parotid saliva following ingestion of fluoride compounds of varying solubility

Healthy dental students received oral doses of 10.0 mg F daily in the form of compounds of widely varying solubilities. Parotid saliva F concentration and urinary F excretion were highest with NaF, Na2PO3F, and SnF2, lowest with CaF2, and intermediate with AlF3. Solubility of the ingested fluoride compound was a controlling factor in the amount of F excreted in the urine, the peak F concentration reached in parotid saliva, and the duration of a significant elevation in salivary F.

Salivary fluoride and calcium concentrations, and their relationship to the secretion of saliva and caries experience

Samples were collected from the stimulated saliva of 113 students enrolled in institutions of higher education. The students were divided into three "carries-diagnostic groups" on the basis of indications given by the Dentocult saliva test, which shows the frequency of lactobacilli and other aciduric microorganisms in saliva. The frequency of such microorganisms in 1 ml saliva in Group A was less than or equal to 103, in Group B greater than 10(3), less than 10(4) and in Group C greater than or equal to 10(4). The rate of secretion of saliva in Group A was significantly higher than in Group C (P less than 0.05). On the average, a rise was noted in the fluoride and calcium concentrations with increasing "caries activity". In the material as a whole, there was a negative and highly significant correlation between the secretion rate of saliva and the concentrations of fluoride and calcium. In the examination by groups, significant correlations were observed between fluoride concentration and rate of saliva secretion in Group A, and with respect to fluoride and calcium only in Group C. The results suggest that the extra salivary fluoride is likely to be derived from the enamel.

A micromethod for the determination of fluoride in blood plasma and saliva

A simple and accurate technique for the determination of fluoride (F-) in capillary-sampled blood is presented. The method is based on the known addition-slope determination technique using the fluoride electrode. No calibration curve or calibration of the electrode is required. A standard deviation of 1.3-5.6% in the range 300-10 ng F/ml was given by 259 duplicate determinations on human plasma. Measurements of parotid saliva showed that it was possible to analayze fluoride concentrations as low as 4 ng F/ml with good reproducibility. The results also show that a 150 microliter sample is sufficient for fluoride determination with high accurary. This method can easily be used in clinical laboratory.

The effects of inorganic ions situated at the enamel surface on the adsorption and activity of acid phosphatase

This study has demonstrated, first, that the affinity of the enamel surface for a biologically active protein-in this case, acid phosphatase-may be modified by first impregnating the mineral with particular inorganic ions. Second, enzymic activity is altered as a function of the inorganic ion incorporated into the enamel surface. Third, strong inhibition of acid phosphatase is demonstrated by ions expected to be released during the carious process which contradicts the postulation that phosphatases are actively hydrolyzing enamel matrix-bound phosphate during the carious attack. Fourth, these results suggest that by incorporating a particular ion into the enamel mineral, a surface with assigned properties may be created which offers some degree of control over subsequent adsorption of organic matter. Thus, it is apparent that by proper selection of inorganic ions and organic macromolecules, both structural properties and biological activities at the enamel-oral fluid interface may be predictably modified.

Fluoride concentrations in saliva after single oral doses and their relation to plasma fluoride

The saliva and plasma fluoride (F) concentrations following intake of different doses of fluoride tablets were studied in six subjects. There was a close relationship between saliva F and plasma F and the ratio was 0.64 +/- 0.01 (s.e.). The plasma half life of F was 4-16 h. This results indicate that saliva F may be a useful substitute for blood sampling in studies concerning the pharmacokinetics of fluoride.

Concentration of fluoride in plaque - a possible mechanism

A mechanism of concentration of fluoride (and phosphate) ions in plaque is suggested: calcium ions from saliva are bound to fixed acidic groups in the plaque, and fluoride (or phosphate) ions are attracted to the bound calcium as counterions. The principle was demonstrated by equilibrium dialysis of calcium-treated acidic ionic exchange material (Sephadex SP and CM) against 1 part/10(6) of fluoride. A part of the fluoride was found to be bound under these conditions.

Fluoride in human parotid saliva

Gustatory stimulation was used to collect parotid saliva in an ascending flow rate pattern. F concentration was found to be independent of rate of flow. The F level in unstimulated parotid saliva, collected before the stimulate samplings, was significantly (P less than 0.01) higher than that for the stimulated collections. It is suggested that this is an apparent increase based on the movement of water out of the lumen, which is in turn triggered by sodium reabsorption. The level of F in unstimulated saliva increased almost tenfold within one hour after the oral administration of 10 mg of F, and a significant (P less than 0.01) increase persisted even at 24 hours after administration of the dosage.

Fluoride in dog parotid saliva after intravenous administration of sodium fluoride, sodium monofluorophosphate, and calcium fluoride

Sodium fluoride, sodium monofluorophosphate, or calcium fluoride, in amounts equivalent to 0.5 mg/kg, were given intravenously to dogs and the effect on parotid saliva F was determined. Significant (P less than 0.01) differences in saliva F levels were related to the ionization of NaF, the hydrolysis of the PO3F ion, and the insolubility of CaF2.

A micro method for direct determination of ionic fluoride in body fluids with the hanging drop fluoride electrode

A simple method for direct determination of ionic fluoride in 5 mul samples of body fluids with the hanging drop fluoride electrode, using sodium acetate buffer (pH 4.8) is described. The hanging drop electrode should prove useful in experimental investigations employing small laboratory animals and in clinical laboratories.

A study of inorganic constituents in dental plaque

The presence of human enamel did not affect the inorganic composition of plaque grown under standardized conditions on an intraoral device. Only enamel recently topically treated with fluoride increased plaque-fluoride concentrations beyond the average value of 25 ppm dry weight (about a tenth of previously reported values).