MERCURY DENTAL FILLINGS ARE NOT DANGEROUS

TOOTH decay begins with bacteria in plaque, a thick substance that sticks to teeth and gums. These bacteria interact with starches and sugars in food to erode the outer surface of the tooth, causing holes (cavities). If untreated, cavities can cause pain, inflammation and tooth loss.

To treat cavities, dentists drill out the decayed material and fill the hole with either a composite resin — which is the colour of teeth and made from the sap of fir and pine trees — or an amalgam, which is silver in colour and made by mixing powdered tin, copper and silver with liquid mercury.

Amalgams can be placed more quickly than resins and mercury also slows the growth of bacteria, making it less likely the tooth will erode further. But despite their advantages, mercury amalgams have always been controversial as, in some forms, mercury is toxic.

Mercury dental fillings can also be vaporised after brushing teeth or eating acidic foods.

So, the question is: does mercury vapour from amalgams cause harm? The World Health Organisation (WHO) has adopted a safety limit for mercury vapour of 25 micrograms (μg) per square metre of air per day.

Given that symptoms of mercury toxicity have never been observed below exposures of 100μg of mercury per square metre per day, the WHO guideline provides a margin of safety. The quantity of mercury found in the mouths of people who have at least eight mercury fillings is about 1μg per day, at least 100 times less than levels found to be harmful.

To put this in perspective, people typically eat or drink about 3.5μg of mercury every day (it is in our water supply and in fish such as swordfish and tuna, for example).

Therefore, the quantity we consume is more than three times greater than the quantity of mercury vapour we inhale from mercury fillings.

And both these sources of mercury are well within ranges shown to be safe.