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.

Factors affecting dentifrice use and ingestion among a sample of U.S. preschoolers

PURPOSE

This study was performed to assess the actual amount of dentifrice used and ingested and factors associated with use/ingestion among 28 U.S. preschoolers aged 40 to 48 months.

METHODS

Using their regular dentifrice brands/flavors and small child-sized toothbrushes (Oral -B 5), the participants or their parents placed dentifrice on toothbrushes three times to assess the quantity used and its consistency. Their brushing behaviors were observed and the amounts of dentifrice ingested were indirectly measured. Afterward, the parents and children placed a "pea-sized" amount of dentifrice on their toothbrushes.

RESULTS

The participants were generally consistent in quantity applied, averaging 0.256 g (range 0.035 g-0.620 g; standard deviation 0.177 g) of dentifrice per brushing. Children, either alone or with parental assistance, placed more dentifrice than either mother or father alone (P = 0.007). The estimated mean ingested fluoride was 0.17 mg F per brushing, an average of 62% of the amount of dentifrice used (range up to 98%). Amount of ingested fluoride was positively associated (P < 0.05) with the amount of dentifrice used, and negatively associated with parental assistance in brushing. When asked to apply a pea-sized quantity, the mean quantity applied was 0.314 g (range 0.064 g-0.521 g).

CONCLUSIONS

This study further supports the use of small amounts of dentifrice in young children, because they ingest substantial proportions of dentifrice.

Assessing fluoride levels of carbonated soft drinks

BACKGROUND

Dental fluorosis occurs as a result of excessive total fluoride intake during tooth development. Some children may receive substantial intake from soft drinks, but few studies have reported fluoride levels in soft drinks. The authors examined the fluoride concentrations of 332 soft drinks.

METHODS

Soft drinks were purchased from Iowa grocery stores. To identify production sites, the authors recorded product details and batch numbers. After decarbonating the drinks, the authors assayed samples for fluoride content using a fluoride ion-specific electrode, and reported the results in parts per million, or ppm, using appropriate standards and duplicate assessments. Descriptive statistics were used to summarize the findings.

RESULTS

The fluoride levels of the products ranged from 0.02 to 1.28 ppm, with a mean level of 0.72 ppm. Fluoride levels exceeded 0.60 ppm for 71 percent of the products. Results varied substantially by production site, even within the same company and for the same product. There were no substantial differences between flavors or between diet and regular soft drinks.

CONCLUSIONS

The majority of soft drinks had fluoride levels exceeding 0.60 ppm. Variation in fluoride levels probably is due largely to the different water sources used in production.

CLINICAL IMPLICATIONS

With no fluoride levels marked on the soft drink products or easily available from the manufacturers, it is not possible for clinicians or consumers to directly estimate fluoride ingestion from carbonated beverages. Therefore, to reduce the risk of dental fluorosis, dental and medical practitioners should be cautious about prescribing dietary fluoride supplements to preschool-aged children in nonfluoridated areas who consume large quantities of carbonated soft drinks.

Remineralization of root surfaces demineralized in solutions of differing fluoride levels

The beneficial effects of fluoride on enamel have been well documented. However, limited data are available concerning the amount of fluoride required for beneficial effects on tooth root. Although studies have shown that fluoride inhibits root demineralization, the aim of this study was to investigate the location, extent and amount of remineralization on root dentin substrates after demineralization has occurred. The root surfaces of extracted human teeth were demineralized in a pure chemical buffer containing varying concentrations of sodium fluoride. After this lesion initiation, the same root sections were then placed into a remineralizing solution. The root sections were characterized after demineralization, and again after remineralization, by polarized light microscopy (PLM) and microradiography (MRG). Lesion depths after the demineralization phase were found to be inversely proportional to the fluoride concentration. When fluoride was present, bands or lines within the body of the lesion were observed with PLM and MRG. Using quantitative MRG, variations in mineral content and distribution were recorded. Examination of the root sections after the remineralization phase showed remineralization to have occurred on the remaining mineral and not on organic matrix devoid of mineral. The amount and location of mineral deposition may be of great significance in the arrestment and treatment of in vivo root surface caries.

Salivary fluoride levels in overdenture wearers after topical fluoride gel application

This study describes salivary fluoride levels after topical fluoride gel application on overdenture abutments. Fluoride levels were evaluated separately for the subjects with normal unstimulated salivary flow rate (n = 16) and for those with a low flow rate (n = 8). One drop of fluoride gel (Karigel-N, Lorvic) was placed in two abutment depressions of the duplicated overdenture, after which unstimulated whole saliva was collected for 30 minutes. Samples for fluoride analysis were taken at 5-minute intervals. Two additional samples were taken at 45 and 60 minutes. Fluoride concentration at the abutment-denture interface (remaining fluoride concentration) was measured at the end of the study. Salivary fluoride concentrations decreased gradually in both groups of subjects, but after 1 hour they remained at a higher level in subjects with low flow rates. Subjects' salivary flow rates correlated negatively with remaining fluoride concentration at the denture-tissue interface. Consequently, mean remaining fluoride concentration was significantly higher in subjects with low flow rate than in their normal counterparts.

Fluoride concentrations of infant foods

Infants who ingest high amounts of fluoride can be at risk of dental fluorosis. The authors analyzed the fluoride concentration of 238 commercially available infant foods. Fluoride concentrations ranged from 0.01 to 8.38 micrograms of fluoride per gram, with the highest fluoride concentrations found in infant foods containing chicken. Infant foods, especially those containing chicken, should be considered when determining total fluoride intake.

Assessing fluoride concentrations of juices and juice-flavored drinks

Few studies have investigated fluoride exposures from juices and juice-flavored drinks manufactured with water. In this study, the authors analyzed 532 juices and juice drinks for fluoride. Fluoride ion concentrations ranged from 0.02 to 2.80 parts per million, in part because of variations in fluoride concentrations of water used in production. Children's ingestion of fluoride from juices and juice-flavored drinks can be substantial and a factor in the development of fluorosis.

Infants' fluoride ingestion from water, supplements and dentifrice

Concerns about dental fluorosis and the paucity of detailed fluoride intake data prompted this longitudinal study of fluoride intake in infants from birth to 9 months of age. On average, water fluoride intake greatly exceeded that from dietary fluoride supplements or fluoride dentifrice. However, fluoride supplements and dentifrice contributed substantial proportions of fluoride intake among children using them. Some children had estimated fluoride intake from water, supplements and dentifrice that exceeded the recommended "optimal" intake (a level that has yet to be determined scientifically). Practitioners should estimate fluoride ingestion from all these sources if considering systemic fluoride supplementation.

Water and formula fluoride concentrations: significance for infants fed formula

The independent contributions of formula and water to the total fluoride (F) intake from the diet of formula-fed infants is not fully documented. Although the precise timing and mechanism by which dental fluorosis occurs has not been fully defined, water F levels can be an important consideration in the risk of dental fluorosis for formula-fed infants. An assessment of 1,308 participants younger than 2 years old revealed that: 81% of homes received public water; 19% received well water; 26% of participants used bottled water; and 11% used some kind of filtration system. In this study, virtually all formulas consumed by the birth cohort and water sources used in the reconstitution of these formulas were assayed for F using a F ion specific electrode and direct read method, except for soy-based formulas, which were analyzed by microdiffusion (modified Taves). Among 78 commercially available bottled waters in Iowa, F levels ranged from 0.02 to 1.36 ppm (mean 0.18 ppm), 83% from 0.02 to 0.16 ppm, 7% from 0.34 to 0.56 ppm, 1% had a F level of 0.88, and 9% had F levels > 1.0 ppm. Among 47 casein (milk)-based formulas, 16 ready-to-feed (RTF) formulas had levels of 0.04-0.55 ppm F (mean 0.17 ppm), 14 liquid concentrates (LC) reconstituted with distilled water had levels of 0.04-0.19 ppm F (mean 0.12 ppm), and 17 powdered concentrates (PC) reconstituted with distilled water had levels of 0.05-0.28 ppm F (mean 0.14 ppm). The 17 soy-based formulas had a range of 0.04-0.47 ppm F (mean 0.26 ppm).(ABSTRACT TRUNCATED AT 250 WORDS)

Infants' fluoride intake from drinking water alone, and from water added to formula, beverages, and food

In infants, the majority of total ingested fluoride is obtained from water, formula and beverages prepared with water, baby foods, and dietary fluoride supplements. Few studies have investigated the distribution of fluoride intake from these sources among young children at risk for dental fluorosis. The purpose of this study was to assess estimated water fluoride intake from different sources of water among a birth cohort studied longitudinally from birth until age 9 months. Parental reports were collected at 6 weeks, 3 months, 6 months, and 9 months of age for water, formula, beverage, and other dietary intake during the preceding week. Fluoride levels of home and child-care tap and bottled water sources were determined. This report estimates daily quantities of fluoride ingested only from water--both by itself and used to reconstitute formula, beverages, and food. Daily fluoride intake from water by itself ranged to 0.43 mg, with mean intakes < 0.05 mg. Water fluoride intake from reconstitution of concentrated infant formula ranged to 1.57 mg, with mean intakes by age from 0.18 to 0.31 mg. Fluoride intake from water added to juices and other beverages ranged to 0.67 mg, with means < 0.05 mg. Estimated total daily water fluoride intake ranged to 1.73 mg fluoride, with means from 0.29 to 0.38 mg.

Comparisons of in vitro root caries models

The purpose of this article is to compare various model systems for the production of in vitro root caries and to assess their ability to simulate the naturally occurring root caries process. Partially saturated buffer models and gel models were evaluated using polarized light microscopy and both qualitative and quantitative microradiography. All model systems showed very similar lesion formation when examined under polarized light. When microradiographs were compared, the systems which contained fluoride, showed clear radiopaque bands within the lesion. The bands, which occurred only in the presence of fluoride, appeared to be due to remineralization. When using an in vitro system that simulates the natural root caries process, it is imperative to understand the components of the particular model, as well as its limitations, and to be aware of the need for more than one evaluative technique.

Effect of proteolytic enzymes on caries lesion formation in vitro

This study investigates enzyme degradation of collagen at various pH levels and is designed to obtain information pertaining to the effect of proteolytic enzymes on caries-like lesion formation and progression. One hundred and eight sections of human teeth with exposed areas on enamel and root face, were placed into an enzyme/buffer system maintained at pH levels of 4.0, 5.5 and 7.0. Periodically, throughout the experimental period, sections were removed and examined histologically for caries-like lesion formation. Results showed consistent surface erosion occurring on the root face only at a pH level of 5.5 in buffer containing enzymes. Sections placed in pH 5.5 buffer only, which served as controls, showed obvious lesion formation on the root face, but with histologically intact surfaces. This interaction occurring between enzymatic activity and acid demineralization suggests that enzymes may have a contributory effect on caries lesion formation in root surfaces.

Natural root caries: a histologic and microradiographic evaluation

The purpose of this study was to obtain information about the detailed histopathology of naturally occurring root caries. Fifty extracted human teeth exhibiting some degree of root caries were sectioned longitudinally and examined with transmitted light, polarized light and microradiography. The occurrence of the histological zones of dentinal caries was tabulated and revealed a lesion body in all cases. Light microscopy showed the same basic features as microradiography and was most useful when the sections were imbibed in quinoline. A structureless area below the main body of the lesion was observed in 77% of the cases when using quinoline. This fluid more clearly defined the extent of the lesion and may show a "phenolic reaction" when using polarized light microscopy. Partial radiopaque surface layers were observed in almost 80% of the sections. This study has described the detailed histopathology of root caries, and aids in the development of model systems to evaluate this emerging dental health problem.