2.7 Fluorine (F)
Fluoride ions (F − ) are rare in foods, though some are found in tea and in seafood. However, fluoride does occur naturally in some water supplies, derived from the rocks through which the water flows. Its only role in the body appears to be to help to protect teeth from decay.
The stages of tooth decay are as follows:
bacteria live in saliva on teeth (form plaque)
produce lactic acid → dissolves calcium salts in tooth enamel
produce protein-digesting enzymes → destroy enamel protein
eventually enamel surface of tooth is breached
underlying softer dentine is attacked
cavities form in the teeth.
The main structural chemical in the enamel of teeth is the same as that in bone. Look back to the section on calcium to identify the chemical and its important component elements.
It is called hydroxyapatite, and contains the minerals calcium and phosphorus, as well as oxygen and hydrogen.
Acid dissolves the hydroxyapatite, a process called demineralisation. Once the acid has been neutralised by the saliva, the minerals can be restored to the tooth surface in a process called remineralisation. However, too many sugary foods mean that there is insufficient time for this remineralisation to occur completely and the tooth begins to decay. It is thought that fluoride helps to prevent this decay in several different ways:
As the enamel is developing in children's teeth, if fluoride is present, it replaces the OH (hydroxy-) part of hydroxyapatite, forming fluoroapatite, which is harder and more resistant to decay.
When the remineralisation process is occurring in the presence of fluoride, again the newly formed enamel is stronger.
Fluoride becomes concentrated inside the plaque bacteria, which reduces their ability to produce acid, so less demineralisation of the teeth occurs.
There is some evidence that children who grow up in areas where fluoride is present in the water have shallower grooves in the biting surfaces of their teeth, thus reducing the places where bacteria can lodge to form plaque.
It seems likely that the remineralisation effect (2) is the most important and so the control of sugars in the diet and the regular use of fluoride toothpaste, to supplement fluoride in the water, are the best preventative measures.
For the protection of teeth, the optimal level of fluoride in drinking water is 1 gram of fluoride per million grams of water (abbreviated to 1 part per million or 1 p.p.m.). In areas where fluoride levels are naturally low, this mineral can be added to the water supply, as it is in some areas of the UK. However, there is some controversy about this measure due to concerns that fluoride could be in some way harmful to health, although there is no scientific evidence to support that claim. The only adverse effect of fluoride appears to be that when fluoride intake is too high, children's teeth can become mottled with opaque white patches (dental fluorosis). The teeth remain functionally normal and resistant to decay and only their appearance is affected.