Low-fluoride Water Research Articles

A Door-to-Door Prevalence Survey of Dental Fluorosis in Tindigani, a Village in the Hai District of Northern Tanzania.

Fluoride in excess of the World Health Organisation limit of 1.5mg/L in drinking water can cause dental fluorosis (DF) in developing teeth. DF is a significant problem in the Hai District of Northern Tanzania, where there is limited access to safe piped water and groundwater is high in fluoride. A door-to-door prevalence survey of residents of Tindigani village was undertaken to assess current prevalence and severity of DF in the Hai District, and the effectiveness of previous interventions to promote low-fluoride drinking water, following a prevalence survey in 2009. DF was graded by trained assessors, utilising dental photography, and drinking water sources were sampled for chemical analysis. DF was endemic in the 563 people assessed, with a prevalence of 79.4% (CI=76.1-82.7%). Prevalence and severity were found to be higher in permanent teeth than deciduous teeth. Fluoride concentrations in non-piped water sources ranged from 2.5-38.6mg/L. Despite more households reporting the use of low-fluoride, piped water sources, compared to 2009 (82.8% versus 62%), DF remains a significant problem in Tindigani and other such communities where low-fluoride drinking water is not easily and reliably accessible. Policy makers must prioritise reliable access to low-fluoride water, especially for children as their permanent dentition develops.

Hydrochemical evolution and assessment of groundwater quality in fluorosis-affected area, Mandla District, central India

Deterioration of groundwater quality is a matter of serious concern today. In Mandla region of central India, fluorosis is common among the local people due to consumption of fluoride-contaminated groundwater. It is, therefore, important to understand the hydrochemical process of contamination and assess the groundwater quality of this region. A total of 173 samples (pre-monsoon and post-monsoon) were collected from borewells and dug wells of different depths for major ions analysis: K+, Na+, Ca2+, Mg2+, Cl−, CO32−, HCO3−, NO3−, SO42−, and F−; along with pH, temperature, TH (as CaCO3), TDS and EC. Broadly, three hydrogeologic units have been identified, viz. Deccan lava flows, infratrappean Lameta and Archean granite and gneiss. In Deccan, two distinct hydrostratigraphic units are Mandla and Dhuma. Mandla is the most prominent and extensive aquifer having hydraulic conductivity 5–15 mday-1 and yield 10–50 m3day−1. Water quality data vis-à-vis well-depth data indicate that Mandla aquifer, lying at a lower elevation than 500 m amsl, is fluoride-contaminated and harmful for human health. Fluoride (41.0% of total samples) and bicarbonate (54.9% of total samples) concentrations in analyzed water are above the global standard for drinking purpose. However, above 500 m msl groundwater is not contaminated with fluoride and is suitable for drinking and irrigation purpose. Fluoride concentration maps depict spatial and seasonal variation. Spatial variation of fluoride in groundwater is due to change in aquifer lithology, varying degree of rock weathering and orientation of structural lineaments. In fluoride concentration map of post-monsoon season, broadening of contour of uncontaminated zone indicates groundwater recharge, which corroborates with water fluctuation map. The fluoride-contaminated water and low-fluoride water are mainly Na–HCO3 and Ca–HCO3 type, respectively. The hydrochemical processes suggest pre-dominance of rock-water interaction; contribution of Na+ and K+ ions in groundwater is due to silicate weathering, whereas Ca2+ and Mg2+ ions are derived due to both silicate and carbonate weathering. Saturation index calculation point towards calcite-dolomite supersaturation and consequent precipitation, along with fluorite dissolution under alkaline condition.

Delineation of groundwater zones with contrasting quality in the fluorotic zone, around Mount Meru, northern Tanzania

ABSTRACT Arumeru district (northern Tanzania) has limited low-fluoride surface water sources for domestic use. Information on the alternative source, groundwater, is also limited in terms of occurrence and quality. Thus, resistivity data in conjunction with hydrochemical data (fluoride, F−; total dissolved solids, TDS; and electrical conductivity, EC) and lithological logs were used to delineate groundwater zones with contrasting quality in the fluorotic zone. The results reveal a thin upper aquifer (~25 m thick) and a lower major aquifer (>100 m thick). Resistivity of 35–60 Ωm represents fresh groundwater hosted in weathered and fractured mafic volcanics, tuffs and breccias. Resistivity of 25–35 Ωm indicates intermediate groundwater quality, whereas resistivity of 15–25 Ωm indicates low groundwater quality (TDS >1000 mg/L, F− >10 mg/L) hosted in lahars. The results have been integrated to develop a groundwater potential index map, to guide local communities, water authorities and government in the planning and development of groundwater resources in the region.

Determining the optimum locations for pumping low-fluoride groundwater to distribute to communities in a fluoridic area in the Upper East Region, Ghana

Groundwater is the primary source of water in the Upper East Region of Ghana, and is generally considered a safe source of drinking water; but there are pockets where the groundwater contains high concentrations of fluoride due to the dissolution of minerals in the local granite. The goal of this study is to evaluate the hydrogeology and hydrogeochemistry of an area where dental fluorosis endemic, in order to identify the optimum locations to pump and distribute low-fluoride groundwater. As expected, the data indicate that the higher elevation recharge areas with outcrops of Bongo granite have elevated concentrations of fluoride in the groundwater (up to 4.6mgL−1), posing the highest risk of fluorosis in the nearby communities. The lower elevation areas, which are the farthest from the Bongo granitic, have the lowest groundwater fluoride (<0.5mgL−1) and the lowest risk of fluorosis. Groundwater flow models suggest that the steady decrease in fluoride is driven by dispersion, with the fluoride concentrations dropping to the World Health Organization's recommended drinking water limit of 1.5mgL−1 at about 400–500m from the source. The optimum locations to install boreholes (or use existing boreholes) for piping low fluoride groundwater to the higher fluoride areas, would be at or beyond this distance. Although the initial costs of developing such a water system would be substantial, this is a potentially viable option for providing low fluoride water to communities suffering from fluorosis.

High fluoride drinking water in Gokwe, northwest Zimbabwe

More than 200 million people worldwide are exposed to excessive fluoride in drinking water. According to the World Health Organization, the optimal concentration range of fluoride in drinking water is 0.5 to 1.5 mg/L. Above this range, populations may contract dental fluorosis or, in severe cases, crippling skeletal fluorosis. In the Gokwe area in NW Zimbabwe, where drinking water contains up to 11 mg/L fluoride, fluorosis prevalence has previously been estimated at 62%. This paper investigates the water quality of 126 water sources in Gokwe (58 pumped boreholes, 15 flowing artesian boreholes, 46 wells and 7 streams). The water chemistry, determined from high performance ion chromatography and field measurements, showed that the water source types exhibit significantly different (P &amp;lt; 0.05) concentrations of F−, Cl−, Na+, K+, Ca2+, Mg2+, temperatures, pH and conductivity values. Thirty-five (28%) of the 126 water sources (18 pumped boreholes, 15 artesian boreholes, one well and one stream) contained F− &amp;gt; 1.5 mg/L, indicating that fluoride contamination in the area is a characteristic of deeper groundwater, possibly due to its interactions with the potentially fluoridic coaly and carbonaceous materials of the Lower Karoo Aquifer at depth. The plausibility of providing alternative low fluoride water, and defluoridation, should be investigated.

Chronic Alcohol Consumption and the Development of Skeletal Fluorosis in a Fluoride Endemic Area of the Ethiopian Rift Valley

This study compared the occurrence of skeletal fluorosis in chronic consumers of locally brewed alcoholic beverages and their matched controls in the Ethiopian Rift Valley. The study revealed that chronic alcohol consumers developed severe forms of crippling skeletal fluorosis quite early in life. The controls were either symptom-free or exhibited mild forms of the fluorosis. The study showed that crippling skeletal fluorosis was directly associated with the large volumes of the locally brewed beer and honey-mead consumption on a daily basis. Chemical analysis of the alcoholic beverages showed that high concentration of fluoride which was much higher than the fluoride in the water was used for the brewing process. From this study one would conclude that in communities residing in high fluoride areas, there should be awareness creation campaigns to point out the relationship of excessive consumption of locally brewed alcoholic drinks and skeletal fluorosis. Regulations should also be put in place to require producers of local alcoholic beverages to use low fluoride water for brewing.

Multi-criteria assessment of community-based fluoride-removal technologies for rural Ethiopia

Elevated concentrations of naturally-occurring fluoride in groundwater pose a serious health risk to millions of people living in the Ethiopian Rift Valley. In the absence of low-fluoride water resources of sufficient capacity, fluoride removal from drinking water is the accepted mitigation option. To date, five different community-level fluoride-removal technologies have been implemented in Ethiopia, although only a few units have been found in a functional state in the field. Which technology should be promoted and up-scaled is the subject of controversial debate amongst key stakeholders. This paper describes a multi-criteria decision analysis exercise, which was conducted with the participation of stakeholders in Ethiopia during a one-day workshop, to assess in an objective and transparent manner the available technology options. Criteria for technology comparison were selected and weighted, thus enabling the participants to assess the advantages and disadvantages of the different technologies and hear the views of other stakeholders. It was shown that there is no single most-preferable, technical solution for fluoride removal in Ethiopia. Selection of the most suitable solution depends on location-specific parameters and on the relative importance given to different criteria by the stakeholders involved. The data presented in this paper can be used as reference values for Ethiopia.

English

Research was carried out at Ngurdoto research station in Tanzania to ascertain the potential development of a water filter made of bauxite, gypsum and magnesite in an attempt to enhance the availability of low-fluoride water. The materials were sourced within Tanzania. The X-Ray fluorescence technique showed that the major components of the materials were: bauxite: Al2O3 (30.33%), SiO2 (15.0%) and Fe2O3 (14.3%); gypsum: CaO (28.09%), SO3 (34.96%), and SiO2 (9.01%); and magnesite: MgO (34.57%) and SiO2(19.3%). The materials were calcined at 350, 400, 450 and 500°C. The activated materials were then mixed in mass ratios of 1:2:3, 1:3:2, 2:1:3, 2:3:1, 3:1:2 and 3:2:1 (bauxite: gypsum: magnesite). One gram of each composite was employed in the batch defluoridation of 1 L of water with fluoride concentration of 12.62 mg/L. The highest defluoridation capacity, 11.89 mg F-/g, was obtained with the 3:2:1 to 500°C composite. The quality of the treated water fell short of WHO standards on sulphates and iron but residual concentrations of Cl-, Al3+, Ca2+, Mg2+, Fe2+ were within the prescribed limits. Sorption behavior followed strongly to Langmuir isotherm, except for the 450°C calcined samples for which the Temkin isotherm behavior was pronounced. Despite the limitations of high residual sulphates and iron, a composite filter of bauxite, gypsum and magnesite was shown to be workable. Key words: Defluoridation, bauxite, gypsum, magnesite, composite, calcine, isotherm.

Change of urinary fluoride and bone metabolism indicators in the endemic fluorosis areas of southern china after supplying low fluoride public water

BackgroundFew studies have evaluated health impacts, especially biomarker changes, following implementation of a new environmental policy. This study examined changes in water fluoride, urinary fluoride (UF), and bone metabolism indicators in children after supplying low fluoride public water in endemic fluorosis areas of Southern China. We also assessed the relationship between UF and serum osteocalcin (BGP), calcitonin (CT), alkaline phosphatase (ALP), and bone mineral density to identify the most sensitive bone metabolism indicators related to fluoride exposure.MethodsFour fluorosis-endemic villages (intervention villages) in Guangdong, China were randomly selected to receive low-fluoride water. One non-endemic fluorosis village with similar socio-economic status, living conditions, and health care access, was selected as the control group. 120 children aged 6-12 years old were randomly chosen from local schools in each village for the study. Water and urinary fluoride content as well as serum BGP, CT, ALP and bone mineral density were measured by the standard methods and compared between the children residing in the intervention villages and the control village. Benchmark dose (BMD) and benchmark dose lower limit (BMDL) were calculated for each bone damage indicator.ResultsOur study found that after water source change, fluoride concentrations in drinking water in all intervention villages (A-D) were significantly reduced to 0.11 mg/l, similar to that in the control village (E). Except for Village A where water change has only been taken place for 6 years, urinary fluoride concentrations in children of the intervention villages were lower or comparable to those in the control village after 10 years of supplying new public water. The values of almost all bone indicators in children living in Villages B-D and ALP in Village A were either lower or similar to those in the control village after the intervention. CT and BGP are sensitive bone metabolism indicators related to UF. While assessing the temporal trend of different abnormal bone indicators after the intervention, bone mineral density showed the most stable and the lowest abnormal rates over time.ConclusionsOur results suggest that supplying low fluoride public water in Southern China is successful as measured by the reduction of fluoride in water and urine, and changes in various bone indicators to normal levels. A comparison of four bone indicators showed CT and BGP to be the most sensitive indicators.

Evaluation of fluoride bottled water and its incidence in fluoride endemic and non endemic areas

Summary Background & aims Water is a vital element for hydratation of the human body. Access to drinking water of good quality became a real problem in many areas of the world and more particularly in Algeria. In the eastern zone of northern Sahara, several epidemiological investigations have revealed the existence of an endemic fluorosis problem associated to excess of fluoride in drinking water. However, in some areas of North Algeria, the prevalence of tooth decay is estimated at 67% in school-children that consume low fluoride water. Thus, the best choice for the population is to consume the local mineral or spring bottled waters although they are expensive. Considering the large variety of the sources of bottled waters in Algeria and the lack of data regarding fluoride content in these waters, it becomes essential to evaluate the fluoride concentration of the consumed water, in order to ensure its benefits on the prevention of caries without incurring the risk of dental or osseous fluorosis. Thus, the aim of this study is to determine the fluoride concentration in bottled waters sold in Algerian market and compare with the stated value in the label. Methods Twenty nine commercial brands of bottled waters were collected from various markets in Algeria. Potentiometric method using a fluoride selective ion electrode (ELIT 8221F − 41936) is carried out to evaluate fluoride content of the water samples. Three readings were taken for each brand and the average was estimated and also compared with the fluoride content printed on the label. Results The obtained results revealed that the fluoride concentration of Algerian bottled waters is ranged from 0.19 ± 0.02 to 1.07 ± 0.026 mg/L. Almost half of the bottled waters (48.28%) did not exceed 0.5 mg F − /L and 37.93% were weakly fluoridated (≤0.3 mg F − /L). Only three (3) among twenty nine (29) brands of bottled waters tested have specified the fluoride concentration on their labels. Conclusions The results show that Algerian bottled waters can be regarded as a relevant source of dietary fluoride. Significant differences were found in fluoride concentration of bottled waters tested. These data are essential to consumer and all health care professionals especially dentists.

Fluoride enrichment mechanism and geospatial distribution in the volcanic aquifers of the Middle Awash basin, Northern Main Ethiopian Rift

Considering the anomalous concentration of fluoride in the ground waters of the Middle Awash basin, a comprehensive survey of the enrichment mechanism as well as its association with common hydrochemical variables was conducted using multivariate statistical methods, Hierarchal Cluster Analysis (HCA) and Principal Component Analysis (PCA). The HCA results indicate a marked heterogeneous spatial distribution of the fluoride concentration, the magnitude of which varies more gradually in the SSW–NNE direction along the Wonji Fault Belt (WFB) than it does in the E-W direction away from this belt. This is strongly associated with the geothermal anomaly that is prominent in the basin interior area. Furthermore, the PCA results show that the magnitude of the fluoride concentration is higher in the groundwater derived from non-calcium bearing aquifers, which are widely distributed in the rift floor. Hydrochemical processes involving a cation exchange reaction cause a systematic Ca 2+ removal from solution from highland towards the rift floor. This geochemical reaction enhances the fluoride enrichment of groundwater along the same flow direction. In this regard, the geothermal belt of the basin interior area is a hydrogeological block marked by high loads of fluoride whereas the plateau areas are low-fluoride zones. The geospatial distribution of fluoride at the basin scale was estimated using the kriging procedure. Appropriate discrimination between local and regional aquifers is important in order to secure low-fluoride water supply for the community in the basin.

Assessing a Potential Risk Factor for Enamel Fluorosis: A Preliminary Evaluation of Fluoride Content in Infant Formulas

The authors conducted a study to determine concentrations of fluoride in infant formulas, and to estimate fluoride intake in infants consuming predominantly formula. The authors compared estimated fluoride ingestion with the tolerable upper limit and adequate intake level for fluoride recommended by the Institute of Medicine (IOM). The authors analyzed fluoride concentrations of powdered and liquid formula concentrates and ready-to-feed formulas. They estimated the total fluoride ingested by infants by considering the fluoride content measured in both the infant formula and various concentrations of fluoridated water. They based consumption volumes on published recommendations. The authors compared estimates for fluoride ingestion with the upper tolerable limit and adequate intake level, which they calculated by using published infant growth charts. Fluoride concentrations of the different formulas were low and, if reconstituted with low-fluoride water, would not result in ingestion of fluoride at levels exceeding the IOM's upper tolerable limit. Some infants aged between birth and 6 months who consume powdered and liquid concentrate formulas reconstituted with water containing 1.0 part per million fluoride likely will exceed the upper tolerable limit of fluoride. When powdered or liquid concentrate infant formulas are the primary source of nutrition, some infants are likely to exceed the recommended fluoride upper limit if the formula is reconstituted with water containing 1.0 ppm fluoride. On the other hand, when the fluoride concentration in water used to reconstitute infant formulas is below 0.4 ppm, it is likely that infants between 6 and 12 months of age will be exposed to fluoride at levels below IOM's recommended adequate intake level.

Dental fluorosis in children in areas with fluoride-polluted air, high-fluoride water, and low-fluoride water as well as low-fluoride air: A study of deciduous and permanent teeth in the Shaanxi province, China

Objective. The aim of the study was to assess dental fluorosis (DF) in the deciduous and permanent teeth of children in areas with high-F coal (area A) and high-F water (area C) compared to children from area B, with low-F water and coal. Material and Methods. 596 children were examined. DF was assessed by TF-score. F-content of indoor air, drinking water, coal, tea, rice, and maize was analyzed. Results. F-content of air and coal ranged from 3.2 µg/m3 and 25.8 mg/kg (area B), 3.8 µg/m3 and 36.3 mg/kg (area C) to 56.8 µg/m3 and 713.1 mg/kg (area A). Likewise, mean F-content of water ranged from ∼0.50 mg/l (areas A and B) to 3.64 mg/l (area C). F-content of tea leaves was similar in all three areas. Maize and rice contained <5 mg F/kg. Prevalence of primary teeth with DF was 49.1%, 2.0%, and 66.8% in areas A, B, and C, respectively. Similarly, DF was found in 96.7% (area A), 19.6% (area B), and 94.4% (area C) of the permanent teeth. Severe fluorosis (TF ≥ 5) was found in area A (47.0%) and area C (36.1%) (p<0.01). Early erupting teeth had slightly higher mean TF-scores in area A than in area C. Conclusions. DF was prevalent in both dentitions in areas A and C. Similarity in percentages of DF may indicate that indoor air with ∼60 µg F/m3 and drinking water with 3.6 mg F/L are similarly toxic to developing permanent teeth. The percentage of deciduous teeth with DF was significantly lower in area A compared to area C. Where low-F coal and low-F water were used (area B), ∼20% of permanent teeth had DF, indicating a relatively low tolerance to fluoride in Chinese children brought up under the present living conditions.

Dental Caries and Dental Fluorosis Experience after Change from High Fluoride to very 6 low fluoride water source in Gadag Town, India

Dental Caries and Dental Fluorosis Experience after Change from High Fluoride to very 6 low fluoride water source in Gadag Town, India

Tealeaves may release or absorb fluoride, depending on the fluoride content of water

As the tea plant ( Camellia sinensis) is known to accumulate fluoride from the soil, the tealeaves may contain high concentrations of fluoride, which is easily released during infusion. In this study, we have tested the possible effect of original fluoride concentration in the water on the fluoride release from tea. Moreover, we wanted to test the possible capacity of tealeaves (commercially available tea) to absorb fluoride from high-fluoride water. In low-fluoride water, fluoride is easily released from tealeaves. Depending upon the fluoride content of the water, dried tealeaves are able also to absorb fluoride. Thus, if a cup of tea is made from high-fluoride water, the fluoride concentration of the infusion may actually be lower than the original fluoride concentration of the water.

Dental fluorosis and dental caries in permanent teeth: rural schoolchildren in high-fluoride areas in the Shaanxi province, China

Objectives. To study the dental fluorosis and caries in the permanent teeth of 12 to 13-year-old children in fluorosis-endemic areas; to assess the relationship between fluorosis and the fluoride content of the drinking water and the relationship between caries and the fluoride content of the water; finally, to analyze the effect of fluoride intake and water stored in clay pots on dental fluorosis. Material and methods. 477 children were divided into 5 groups (A to E) according to the fluoride concentration of the waters, i.e. by 0.4, 1.0, 1.8, 3.5, and 5.6 mg F/l, respectively. Dental fluorosis was assessed by TF score and caries by the DMF-T index. A questionnaire was used to obtain information about water storage and other information relevant to children's fluoride intake. Results. A positive relationship was found between the mean TF scores and the water fluoride concentration. In groups B and D, the TF score was higher in 13-year-olds than in 12-year-olds. Caries prevalence and mean DMF-T ranged from 2.6% and 0.03 (group E) to 22.1% and 0.38 (group A). Storage of water in clay pots seemed to increase the severity of fluorosis slightly, and to decrease the caries prevalence. Conclusions. Defluoridation of drinking water, or—alternatively—the provision of low-fluoride water sources, should be given high priority in the examined Shaanxi rural areas. Fluoride concentration of drinking water should be maximum 0.6 mg/l. Storage of water in the local clay pots may increase the severity of dental fluorosis.

Dental fluorosis among persons exposed to high‐ and low‐fluoride drinking water in western Norway

Abstract– The aim of this project was to study the prevalence and severity of dental fluorosis among persons exposed to moderate‐ to high‐ or low‐fluoride drinking water in western Norway, and to assess the risk factors involved. Subjects aged 5 to 18 years who had been lifelong consumers of moderate‐ to high‐fluoride groundwater (≧0.50 mg F/L) were selected for the study (n=113). A comparison group (n=105) was chosen among consumers of low‐fluoride surface water (∼0.10 mg F/L) in the same district. The Thylstrup‐Fejerskov (TF) Index was used to score dental fluorosis. A questionnaire was used to obtain information on fluoride exposure and other relevant factors. Among the consumers of low‐fluoride water 14.3% showed dental fluorosis (TF score 1–2) as compared to 78.8% in the group consuming moderate‐ to high‐fluoride water (TF scores 1–7). Premolars were most frequently affected, but severe cases (TF scores 3–7) were equally prevalent in maxillary central incisors and first molars. In logistic regression analysis with TF score 0 or TF score ≧1 as the dependent variable, only fluoride concentration in the drinking water was associated with a statistically increased risk of dental fluorosis (odds ratio: 18.9; 95% CI: 8.85–40.44). In the study area, which was characterised by multiple fluoride sources, uncontrolled groundwater with moderate to high fluoride content was the most important factor in the development of dental fluorosis. In order to prevent dental fluorosis, groundwater wells should routinely be analysed for fluoride.

Distribution of fluoride and fluorosis in Ethiopia and prospects for control.

A review and mapping of fluoride test data for 270 water sources in 126 communities and examination of the literature of fluorosis distribution in Ethiopia show that this health problem extends beyond the Rift Valley into some highland communities. Fluoride concentrations above 5.0 mg/l in the Rift Valley were found mostly in hot springs (100% of all sources), lakes (78%), shallow wells (54%) and boreholes (35%) and the lowest concentrations (below 1.5 mg/l) in springs and rivers. Analysis of hydrochemical, economic and demographic factors in the spatial distribution of high-fluoride domestic water sources indicates that the fluorosis problem has become more serious in the Rift Valley in recent decades. Considerable spatial variation in the occurrence of fluoride, even within the same communities, and the presence of some low-fluoride water sources in the Rift Valley offer possibilities for geochemical exploration for acceptable domestic sources. The defluoridation programme in the Wonji irrigation scheme illustrates the problems faced by a large rural community in a developing country. Possibilities for control are examined and recommendations made for the development of alternative water sources and promising defluoridation methods using locally available materials and technologies.

Dental fluorosis among persons exposed to high- and low-fluoride drinking water in western Norway.

The aim of this project was to study the prevalence and severity of dental fluorosis among persons exposed to moderate- to high- or low-fluoride drinking water in western Norway, and to assess the risk factors involved. Subjects aged 5 to 18 years who had been lifelong consumers of moderate- to high-fluoride groundwater (> or = 0.50 mg F/L) were selected for the study (n = 113). A comparison group (n = 105) was chosen among consumers of low-fluoride surface water (approximately 0.10 mg F/L) in the same district. The Thylstrup-Fejerskov (TF) Index was used to score dental fluorosis. A questionnaire was used to obtain information on fluoride exposure and other relevant factors. Among the consumers of low-fluoride water 14.3% showed dental fluorosis (TF score 1-2) as compared to 78.8% in the group consuming moderate- to high-fluoride water (TF scores 1-7). Premolars were most frequently affected, but severe cases (TF scores 3-7) were equally prevalent in maxillary central incisors and first molars. In logistic regression analysis with TF score 0 or TF score > or = 1 as the dependent variable, only fluoride concentration in the drinking water was associated with a statistically increased risk of dental fluorosis (odds ratio: 18.9; 95% CI: 8.85-40.44). In the study area, which was characterised by multiple fluoride sources, uncontrolled groundwater with moderate to high fluoride content was the most important factor in the development of dental fluorosis. In order to prevent dental fluorosis, groundwater wells should routinely be analysed for fluoride.

The influence of fluoridation of drinking water on the long-term hearing results of stapedectomy.

The long-term hearing results of stapedectomy were assessed in 294 patients with otosclerosis living in an area where the natural waters have a very low fluoride content. Only patients with an initially successful outcome were included. Patients having an additional known cause of hearing loss were excluded. The mean follow-up period was 9 yr. From the best hearing levels achieved 6 to 12 months after surgery, the mean air conduction thresholds showed an annual impairment of 0.4 to 1.1 dB/year and bone conduction thresholds an annual impairment of 0.5 to 1.0 dB/year. There was no significant difference between patients drinking fluoridated tap water and those drinking low-fluoride water. It is concluded that a daily sodium fluoride intake of 1 to 3 mg in a low-fluoride area is too small to have a significant effect on hearing impairment after stapedectomy.