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9. Does water fluoridation pose risks?

  • 9.1 When can teeth be affected by dental fluorosis?
  • 9.2 Is water fluoridation causing dental fluorosis?
  • 9.3 How can bones be affected by skeletal fluorosis?
  • 9.4 At what intake levels does fluoride cause skeletal fluorosis?

9.1 When can teeth be affected by dental fluorosis?

Dental fluorosis is a condition that results from the intake of excessive amounts of fluoride during the period of tooth development, usually from birth to approximately 6-8 years of age. It is linked to the excessive incorporation of fluoride into dental enamel and dentine which prevents the normal maturation of the enamel. The severity of this condition ranges from very mild to severe, depending on the extent of fluoride exposure during the period of tooth development. Mild dental fluorosis is usually characterized by the appearance of small white areas in the enamel; individuals with severe dental fluorosis have teeth that appear stained and pitted ("mottled").

Dental fluorosis occurs during the period of enamel formation. Exposure to excessive levels of fluoride after tooth development appears to have little influence on the extent of fluorosis.

Re-evaluation of past fluorosis data demonstrated a dose-response relationship and showed that even at low fluoride intake levels from water, a certain level of dental fluorosis will be found. More...

9.2 Is water fluoridation causing dental fluorosis?

Although there has been an increase in the prevalence of dental fluorosis over the past 30 to 40 years, it has generally been attributed to the widespread intake of fluoride from sources other than drinking water, such as toothpastes, mouth rinses, fluoride supplements fluoridated salt or milk, as well as locally applied dental gels, solutions and varnishes on top of the possible exposure from drinking water.

An elevated prevalence of dental fluorosis is observed in certain areas of the world, such as China, where the intake of fluoride may be extremely high, due in large part to the elevated fluoride content of the surrounding geological environment. The consumption of drinking water containing naturally elevated levels of fluoride, the indoor burning of coal rich in fluoride, the preparation of foodstuffs in water containing high fluoride levels and the consumption of specific foodstuffs naturally rich in fluoride, such as tea, all contribute to the elevated intake of fluoride, with the resultant development of dental fluorosis. More...

9.3 How can bones be affected by skeletal fluorosis?

Though the incorporation of fluoride into bone may increase the stability of the crystal lattice, it also delays or inhibits bone hardening (mineralization), causing the bones to become brittle or less able to withstand pressure. The greater the amount of fluoride incorporated into bone, the more severe are the effects associated with skeletal fluorosis.

In a preclinical phase of skeletal fluorosis, the patient may show no other symptoms than a slight increase in bone mass, detected radiographically.

During the first and second clinical stages of skeletal fluorosis, the symptoms are: sporadic pain and stiffness of the joints, chronic joint pain, osteosclerosis of cancellous bone and calcification of ligaments.

During the clinical phase III, associated with crippling skeletal fluorosis, symptoms are: limited movement of the joints, skeletal deformities, intense calcification of ligaments, muscle wasting and neurological deficits.

Other effects of skeletal fluorosis arise when high fluoride intakes overly stimulate bone formation which can result in calcium deficiency, osteomalacia, and secondary hyperparathyroidism.

The development of skeletal fluorosis depends on a number of factors, such as age, nutritional status, renal function and calcium intake, in addition to the extent and duration of exposure to fluoride. Skeletal fluorosis may be reversible to some degree. More...

9.4 At what intake levels does fluoride cause skeletal fluorosis?

The occurrence of endemic skeletal fluorosis in certain areas of the world where the intake of fluoride may be extremely high (e.g., India, China) has been well documented in case reports and surveys. An increased intake of fluoride from foodstuffs and drinking water with high levels of fluoride of geological origin plays a major role. Yet it is difficult to characterize the exposure-response relationship because many other factors may be important such as nutrition and climate, which influence fluid intake, or the indoor burning of coal rich in fluoride (in China).

Indeed, the many studies on human skeletal fluorosis carried out around the world sometimes show significantly different results from one area to another. In most of these studies, only fluoride intake from drinking water seems to have been taken into account. In the USA for instance, only five cases of crippling skeletal fluorosis were reported over the past 40 years. Their total intake of fluoride over a 20-year period was estimated to be approximately 15–20 mg/day.

Studies in India, Senegal and China on populations exposed to drinking water naturally high in fluoride show diverging results. In most studies, fluoride concentrations in drinking water ranging from 1 to 9.7 mg/litre were associated with a varying prevalence of skeletal fluorosis within the range of 0 to 71%.

In India, a study on the dependence of skeletal fluorosis on duration of exposure and age showed that skeletal fluorosis among individuals consuming water with an average fluoride concentration of 9.0 mg/litre started to appear after 10 years of residence in the village and affected all individuals after 20 years.

Studies using bone-fracture as an indicator of increased bone brittleness due to skeletal fluorosis have shown an increased risk of bone fractures at total fluoride intakes of 14 mg/day and evidence suggestive of an increased risk of bone effects at total fluoride intakes above about 6 mg/day. More...

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