Return to Dentistry On-LineDavid Brown, Head of the Department of Dental Materials Science, UMDS Dental School, Guy's Hospital, London SE1 9RT
Summary
Dental amalgam
Dental amalgam has been used for over 150 years to treat the ravages of a preventable disease - dental decay. It is thus a medical treatment, and as such it has been involved in one of the longest clinical trials on record. Unlike many modern drugs or inoculations, which although seeking to cure or prevent more malignant diseases than dental decay, often have had some distressing side effects, and most have several patient deaths within their audit; dental amalgam does not.
The mercury hazard
It's not that the vapour of mercury (which represents half of a silver dental filling) isn't toxic, it's just that the small amount of vapour that can be created from the fillings in the great majority of patients never gets absorbed by their bodies. It is only the chronic exposure to high concentrations of mercury vapour that is a cause for concern. Such conditions are only rarely found in dental surgeries,usually as a result of an undetected spillage of elemental mercury. In such a case, it would be the staff of the surgery who would be at risk, not the patient.
Mercury in fillings
In a set amalgam filling in the mouth the mercury is bound to the other metals - silver, tin and copper in the form of intermetallic compounds. In order to liberate mercury vapour from these fillings they need to have dry surfaces and to be harshly abraded. In most patients these conditions do not occur, and even if they do then dilution effects come into play.
Try this experiment
Just why the conditions for the liberation of mercury vapour from amalgam fillings are so rare can be judged from this simple experiment. Over the period of a minute or so note how many times your teeth come into contact (especially the back ones where amalgams may have been placed); note also whether these contacts are hard or soft. Unless you are annoyed about something or at someone, the majority of these contacts will be soft. What is more you will become aware that there is a layer of lubricating saliva between them . If indeed your teeth contain amalgam fillings they are clearly not rubbing together continuously and they are separated by saliva. Mercury vapour is not going to be evolved under these conditions.
The effects of grinding
If you are a perpetual grinder (a bruxist) you are likely to produce more vapour than a non-grinder. However, you should remember a) the presence of the saliva, b) that most people breathe through their noses, and c) that even those who breath through their mouths expel air rather than inhale it for half the time they are alive.
Food as an abrasive
It is often suggested that the movement of food over amalgams generates substantial quantities of vapour, but with the soft, wet diets of the present century this is unlikely. Small amounts of particulate amalgam may be ingested, but, as indicated by the low wear rate of these materials in the mouth, such losses are very small. Any amalgam that is swallowed is readily dealt with by the human waste disposal unit.
Relative quantities
If none of the above arguments that mercury vapour is not continuously being given off convinces you, consider the dilution effect. The human population of the world between them expels 500 million litres of flatus (anal gases) per day (about 700 ml per person), but despite its characteristic odour, unless we are in close proximity we can't detect it. This is because it is being dumped into a volume of air many orders of magnitude greater than itself - about 250,000 million times to be precise. This dilution effect is also seen with the small amount of mercury vapour given off by amalgam fillings.
A question of degree
If you are at a party and a small fly falls into your drink, you think nothing of flicking it out and you carry on drinking. Because it was so small you have no concern as to what it may have left behind in your drink. Now if the cat did the same it would be analogous to a heated spillage of elemental mercury lying undetected in a dental surgery. That would be a cause for concern.
Mercury monitoring
The periodic monitoring of dental practices is to be recommended, and disposable passive mercury monitors are available from Henry Schein Rexodent in Southall. These can provide a useful, first-level indication of any serious contamination within a dental surgery, and advice on the use of these is available from d.brown@umds.ac.uk