Problems in exposure assessment of fluoride in drinking water

OBJECTIVES: We developed a source documentation approach that identified fluoride content of drinking water at the state or local level to estimate fluoride concentrations from public water systems. We then compared estimates from this approach with estimates obtained from a single source, the 1992 Centers for Disease Control and Prevention (CDC) Fluoridation Census. METHODS: We used residential histories from a case-control study. For each residence we attempted to determine fluoride concentrations using the 1992 CDC Fluoridation Census. For the source documentation method we utilized multiple sources from state and local contacts to verify and collect additional data. We compared the fluoride estimates obtained by the two methods. RESULTS: When fluoride values were found using both methods, there was good correlation (Kendall's tau = 0.85; 95% confidence interval = 0.79, 0.90) and concordance was 96 percent. We obtained over 99 percent of the fluoride values needed using source documentation as compared to 49 percent of the values needed when we used a single publication. When fluoride values were missing using the 1992 CDC Fluoridation Census, 21 percent had source documentation estimates of at least 0.7 ppm. CONCLUSIONS: Researchers need to consider limitations of using a secondary data source to estimate fluoride in drinking water, particularly in studies where exposure to fluoride is the primary exposure of interest.     

Defluoridation of drinking water by boiling with brushite and calcite

Existing methods for defluoridating drinking water involve expensive high technology or are slow, inefficient and/or unhygienic. A new method is now suggested, encompassing brushite and calcite suspension followed by boiling. Our aim was to examine the efficiency of the method and the chemical reactions involved. Brushite, 0.3-0.5 g, and an equal weight of calcite were suspended in 1 litre water containing 5-20 ppm fluoride. The suspensions were boiled in an electric kettle, left to cool and the calcium salts to sediment. Solution ion concentrations were determined and sediments were examined by X-ray diffraction. In distilled water initially containing 5, 10 and 20 ppm fluoride the concentration was reduced to 0.06, 0.4 and 5.9 ppm, respectively. Using Aarhus tap water which contained 2.6 mmol/l calcium the final concentrations were 1.2, 2.5 and 7.7 ppm, respectively, and runs without calcite gave results similar to those with calcite. Without boiling the fluoride concentration remained unaltered, as did the brushite and calcite salts, despite occasional agitation by hand. All solutions were supersaturated with respect to fluorapatite and hydroxyapatite and close to saturation with respect to brushite. Boiling produced well-crystallised apatite and traces of calcite, while boiling of brushite alone left a poorly crystallised apatite. We conclude that boiling a brushite/calcite suspension rapidly converts the two salts to apatite which incorporates fluoride if present in solution, and that this process may be exploited to defluoridate drinking water.     

Determination of optimal fluoride concentration in drinking water in an area in India with dental fluorosis

The present study was made to determine the optimal fluoride concentration in drinking water in a fluorotic zone. The area under study was divided in four parts on the basis of fluorides present in drinking water. A sample of 1320 persons was examined, where prevalence of dental fluorosis varied from 3.8% to 65.4% depending on the fluoride concentration in drinking water. Statistically significant increase in the prevalence of dental fluorosis was found (a) with I he rise in fluoride in drinking water, (b) with the rise in age, peak being found at 15-19 years age group and (c) amongst the bona fide residents of the area. A significant positive correlation was found between fluoride in drinking water and Community Fluorosis Index. While determining the optimal level of fluoride in drinking water, values obtained were 1.05 parts/10⁶, 0.8 parts/10⁶and 0.34 part/10⁶, respectively, by different formulae in a fluorotic zone of western India.     

Simple defluoridation procedures for Kenyan borehole water

Magnesium oxide and bone meal were used as chemical defluoridating agents to reduce excessive amounts of fluoride from artificial water samples which had been prepared to simulate Kenyan water samples with a fluoride concentration ranging from 1 to 9.3 ppm. The water filtrate from bone meal was clear and palatable. The filtrate from magnesium oxide was slightly slimy and cloudy, but palatable. Either of these chemical agents may be used in simple defluoridation procedures in rural and suburban areas using borehole water to reduce the excess fluoride in the water to beneficial non-toxic levels. Both magnesium oxide and bone meal are inexpensive chemicals and readily available in Kenya.     

A map of natural fluoride in drinking water in Pakistan

AIM: The assessment of fluoride levels in domestic water supplies in Pakistan. METHOD: Water samples were collected from sources supplying the majority of the population: taps in places where piped water supply was available, tube-wells, boreholes and wells in rural areas, and stream water where appropriate. RESULTS: Analysis of 987 water supplies showed that they are predominantly low in fluoride content, 84% containing less than 0.7ppm of fluoride. CONCLUSION: For the majority of the population in Pakistan there is a clear indication for use of alternate sources of fluoride to ensure optimal intake necessary for the control of dental caries.     

US drinking water: fluoridation knowledge level of water plant operators

OBJECTIVES: We determined the knowledge level of water plant operators who fluoridate drinking water, and we compared small and large water plants. METHODS: A pretested survey was sent to 2,381 water plant operators in 12 states that adjust the fluoride concentration of drinking water. A z-test for proportion was used to test for statistical difference between small and large plants at alpha = 0.05. Small water plants were those treating less than 1 million gallons of water daily. RESULTS: Eight hundred small and 480 large water plant operators responded, resulting in a response rate of 54 percent. Two-thirds of water plant operators correctly identified the optimal fluoride level, but more than 20 percent used a poor source for choosing the optimal level. Only one-fourth of operators were able to maintain the fluoride concentration to within 0.1 mg/L of the optimal concentration. A significantly greater proportion of operators at large water plants than at small water plants reported that they were able to maintain a fluoride concentration to within 0.1 mg/L of the optimal concentration (33.5% vs 21.3%, z = 4.74, P < .05). CONCLUSIONS: Although most operators correctly identified the optimal fluoride level, small water plant operators were less likely to use accurate reasoning for choosing that level and in maintaining fluoride concentrations within 0.1 mg/L of that level than large water plant operators.     

Determining optimal levels of fluoride in drinking water for hot, dry climates -a case study in Sri Lanka

The prevalence of dental caries and dental fluorosis was examined in 380 14-yr-old children living in four geographic areas of Sri Lanka with water F-levels of 0.09-8.0 ppm. A reduction in caries prevalence by 43% was recorded in children consuming 0.6-0.79 ppm F- compared to those in low fluoride areas (< 0.4 ppm). Among those consuming drinking water containing < 1.0 ppm F-, however, 32% of the children had mild forms and 9% severe forms of dental fluorosis (Dean's index). Although other sources of F- may contribute to this effect, the prevalence and severity of dental fluorosis seen in low fluoride areas was confirmed to be high in rural Sri Lanka. Our data are comparable with recent findings from other tropical countries, e.g. Kenya and Senegal, and reaffirm that WHO guidelines for the upper limit of F- in drinking water may be unsuitable for developing countries with a hot, dry climate. Current knowledge now enables us to recommend 0.8 ppm as an appropriate upper limit for F- in drinking water supplies for these populations.     

Studies on the effect of dentifrices with low fluoride content

The caries prophylactic effect of dentifrices with a low fluoride (F) content has been tested in a 2-year double-blind experiment on 1,150 schoolchildren aged 11–14 years who have had fortnightly F mouthrinses as a basic prophylaxis. Clinical registration of new DMFS and new smooth surface caries showed only insignificant differences for the groups treated with regular, weak or F-free dentifrices. Radiographic investigation showed a tendency towards fewer decayed surfaces in the groups treated with a monofluorophosphate (MFP) dentifrice with regular F content and CaCO₃ as polishing agent, but no significant effect with the corresponding dentifrice with lower F content. In groups treated with a dentifrice with silicon dioxide as the polishing agent both the regular content of MFP and a weak concentration of NaF resulted in fewer radiographically diagnosed carious lesions in the groups of girls, who had a higher caries rate than the boys. These and other data are combined in the Discussion into a hypothetic model for the mode of action of MFP and NaF dentifrices, with a view to continued development towards optimal clinical results with minimal F absorption.     

Endemic fluorosis and partial defluoridation of water supplies – A public health concern in Kenya

Abstract Endemic fluorosis is a public health problem in many parts of Kenya clue to high fluoride content in the drinking water. The Kenyan Government is committed to development of water sources with the object of supplying safe and sufficient water to the entire population by the year 2000. This water will contain high amounts of fluoride thereby increasing the incidence of severe endemic fluorosis in Kenya. Development of procedures for partial defluoridation should therefore be considered. Various defluoridation methods adopted in different places affected with endemic fluorosis are reviewed in the present article, with special reference to problems of operation and limitations in their application.     

Effect of firing temperature and water exposure on crack propagation in unglazed porcelain

Static fatigue of dental ceramics results from the interaction of residual tensile stress and an aqueous environment. This phenomenon is a potential cause of delayed crack formation and propagation in ceramic or metal-ceramic restorations. For dental ceramics, the influence of microstructural defects such as porosity or fissures caused by incomplete sintering is not known. The objectives of this study were to characterize the influence of porosity (produced by underfiring) on the crack propagation resistance of two feldspathic porcelains and to determine whether lower stress corrosion susceptibility or higher fracture toughness accounts for the superior thermal shock resistance of one of these ceramics. We underfired bars of each porcelain, 25 mm x 4 mm x 4 mm, by as much as 84 degrees C below their recommended firing temperatures. After polishing the specimens through 0.05 microns alumina, we induced cracks in their surfaces with a Vickers microhardness indenter. Semicircular cracks, which were produced under an applied indenter load of 19.6 N, grew with time during storage in distilled water at 37 degrees C. Underfiring of both ceramics caused a slight increase in fracture toughness and a relatively small change in pore volume fraction until we underfired the ceramics at 30 degrees C or more. The crack propagation data indicate that the higher thermal shock resistance of one of the ceramics--as measured previously by a water-quench technique-may be due to its greater resistance to stress corrosion at the initial stage of crack propagation.     

The effect of water purification systems on fluoride content of drinking water

Objective: The purpose of the present study was to determine the effect of different water purification systems on the fluoride content of drinking water and to compare the efficacy of these water purification systems in reducing the fluoride content. Materials and Methods: Five different water purification systems were tested in this study. They were reverse osmosis, distillation, activated carbon, Reviva (R) , and candle filter. The water samples in the study were of two types, viz, borewell water and tap water, these being commonly used by the people of Davangere City, Karnataka. The samples were collected before and after purification, and fluoride analysis was done using fluoride ion-specific electrode. Results: The results showed that the systems based on reverse osmosis, viz, reverse osmosis system and Reviva (R) showed maximum reduction in fluoride levels, the former proving to be more effective than the latter; followed by distillation and the activated carbon system, with the least reduction being brought about by candle filter. The amount of fluoride removed by the purification system varied between the system and from one source of water to the other. Interpretation and Conclusion: Considering the beneficial effects of fluoride on caries prevention; when drinking water is subjected to water purification systems that reduce fluoride significantly below the optimal level, fluoride supplementation may be necessary. The efficacy of systems based on reverse osmosis in reducing the fluoride content of water indicates their potential for use as defluoridation devices.     

Caries-preventive effect of two concentrations of stannous fluoride mouthrinse

The effectiveness of a stannous fluoride mouthrinse, when used once each school day, was investigated in a 3-year study. Effervescent stannous fluoride tablets of two concentrations were dissolved in 20 ml of water, giving solutions of 100 parts/10(6)F- and 200 parts/10(6)F- respectively. Approximately 1,200 children, with a mean age of 10 years, were divided on a random basis into three groups. Two of the groups rinsed with the two strengths of solution and the third group rinsed with a placebo. Examinations were carried out at the commencement of the study, and at yearly intervals thereafter. The final series was carried out a year after the rinsing procedures were terminated. There were significant reductions in the numbers of new caries in each of the two experimental groups as compared with the controls. The concentration of the solutions appeared to have little influence on the results. More dramatic reductions were noted in the teeth which erupted during the course of the study. A residual effect was demonstrated a year after the rinsing procedures were terminated.     

Three-year report on caries prevention using fluoride varnishes for caries risk children in a community with fluoridated water

Abstract – The Benifit of seminnual application of the sodium fluoride varnish Duraphat^(R) and the silane fluoride varnish Fluor Protector^(R) was studied in 11–13-year-old children with high caries activity and lifelong exposure to fluoridated drinking water (1–1.2 parts/10⁶). Annual clinical and radiographic examinations were made of 62 children in the Duraphat group and 70 children in the Fluor Protector group. Fluoride varnish was applied semiannually using the half-moth technique. After 3 years, for the Duraphat group mean total DMES increments on the control side were 6.2 and on the test side 4.3 ( P <0.001); for the Fluor Protector group the DMES increments were 4.9 and 4.4, respectively (NS). The caries reductions were 30% and 11%. Since ther were no differences between initial mean DMES scores of the groups, it is possible that the lower increment in the Fluor Protector control side compatred to the Duraphat control side was due to fluoride ions from Fluor Protector crossing the midline and providing protection on the control side as well. Therefore, we conclude that Duraphat proved effective, but definite conslusion of the effect of Fluor Protector cannot be made. Children with the highest DMES increment on the control side (duraphat) gained most from the applications.     

Two years'' effect on the primary dentition of mouthrinsing with a 0.2% neutral NaF solution

The benefits to the primary teeth from a school-based fluoride mouthrinsing program are presented. Children in grades 1--4, residents of a fluoride-deficient community in New York, rinsed an average of 49 times during 2 school years using a 0.2% neutral NaF solution. Rinsing was done under the supervision of homeroom teachers. Differences in caries prevalence of 20.0% (dfs/child) or 23.8% (dfs/100s) were found in children who participated in the rinsing program for 2 years compared with baseline caries scores of children who never rinsed. Surface specific differences in caries prevalence after 2 years were: 27.5% for proximal surfaces, 24.1% for buccolingual surfaces, and 12.4% for occlusal surfaces.     

Fluorosis and caries prevalence in a community drinking above-optimal fluoridated water

Fluorosis levels and caries prevalence were evaluated in 182 adolescents aged 15-16 yr residing from birth in an area with 5 ppm fluoride in the drinking water. The mean number of surfaces affected by caries in the total study population was 5.46 DMFS. The teeth most susceptible to caries were the first molars. The prevalence of fluorosis was 100% with 53 subjects demonstrating mild fluorosis (according to Dean's index), 83 demonstrating moderate fluorosis, and severe fluorosis diagnosed in 46 subjects. A statistically significant positive association was found between caries prevalence and fluorosis; the more caries experienced, the more severe the fluorosis level. Boys experienced significantly higher fluorosis levels than girls. Further research will investigate the possible variables which may explain this difference in fluorosis by sex.     

Role of drinking water copper in pathogenesis of oral submucous fibrosis: a prospective case control study

Although oral submucous fibrosis (OSMF) is thought to be multifactorial in origin, the chewing of areca nut is thought to be the main cause. Alkaloids and tannins in areca nut are responsible for fibrosis, but recent evidence has suggested that copper ions are also an important mediator, and in a small pilot study we recently found that OSMF was significantly associated with a raised concentration of copper in drinking water. We have further investigated this association in a heterogeneous population in Hyderabad-Karnataka, India, a region with a high incidence of the condition. We evaluated 3 groups, each of 100 patients: those with OSMF who chewed gutkha, those who chewed gutkha but did not have OSMF, and healthy controls who did not chew gutkha. The difference between the groups in the mean concentration of copper in water measured by atomic absorption spectrometry was significant (p < 0.001). There were also significant differences between the groups in mean concentrations of serum copper, salivary copper, and ceruloplasmin (p < 0.001). Our results confirm that copper in drinking water contributes to the pathogenesis of OSMF, but ingestion of copper is unlikely to be the sole cause.     

Caries preventive effect of a fluoride-containing varnish (Duraphat®) after 1 year's study

ABSTRACT The caries prophylactic effect of semi-annual applications of a fluoride-containing varnish (Duraphat®) was tested in 121 15-year-old children. The children were divided into a test (60 subjects) and a control group (61 subjects). The teeth of the children in the test group were coated with the fluoride varnish at the beginning of the experimental period and again 6 months later. A clinical and radiographic examination of all children was performed immediately prior to the first application of varnish and 1 year later. The mean caries increment was 0.9 new DMFS in the test group and 4.0 in the control group. The difference was statistically significant at the 0.1 % level. The caries prophylactic effect on different tooth surfaces was statistically significant both on proximal and on occlusal surfaces at the 0.1 % level. Analyzing the material with respect to the caries prophylactic effect against the background of caries prevalence at the start of the investigation showed a better effect in the group of children with low and medium initial DMFS values.     

Three-year study of the effect of fluoride varnish (Duraphat) on proximal caries progression in teenagers

Abstract – The effect of sodium fluoride varnish (Duraphat) applications on proximal caries progression was studied during a 3-yr period in 87 teenagers and compared to a control group (n= 107). In the fluoride varnish group the children were treated with fluoride varnish every third month during the experimental period. Caries lesions on the mesial surfaces of first premolars to the mesial surfaces of second molars were recorded annually on radiographs and an individual progression value was calculated. The study showed that topical application of fluoride varnish every third month significantly (p<0.05) reduced the progression of proximal caries lesions in premolars and molars. The most obvious reduction of caries progression was observed among children who developed between two and eight new proximal lesions during the test period. In the children with the highest caries activity (> nine new proximal lesions) Duraphat treatments did not significantly reduce proximal caries progression in premolars and molars.