Bacteria and biofilm — how plaque forms

"Mummy, look – all red!" Who cannot remember the wide, startled eyes of the children in the television advert, bringing their mother the terrible news of proven residues on their teeth? At the dental practice too, deposits are made visible with staining techniques – an important way of showing the possible breeding grounds of germs that damage the teeth

Dental deposits, also known as plaque or, in current dental usage, as "biofilm", consist of bacteria and their metabolic products, food remains and components of the saliva. They are tough, cling firmly to the teeth and offer bacteria and germs an ideal place to nest. The plaque grows, spreads and, after about 48 hours, begins its damaging attack on the enamel. The deposit, at first soft, develops over time into a hard layer that can no longer be removed with a toothbrush: tartar, which spreads further and whose rough surface offers the ideal basis for further bacteria to attach

Under normal conditions there is a complex balance in the healthy mouth between the bacteria on the mucous membrane and those on the tooth surfaces. Various factors can, however, shift this balance considerably. Disease-causing germs can then multiply and develop their damaging effect. Caries-causing bacteria produce substances through which they gain a particularly good hold on the tooth surfaces. That is also why they are an essential component of the deposits. They use carbohydrates for energy and, as they break them down, produce acids as metabolic products. These acids dissolve calcium and phosphate out of the enamel and make it less resistant

Whether caries develops, and how severely, is decided by the interplay of plaque bacteria and the food available – sugar above all. The metabolism of the bacteria produces acid, which is deposited on the tooth surface. Enamel is indeed very resistant, but it is not invulnerable. Acids can affect it severely: they dissolve minerals out of it and so soften it

And although saliva can neutralise acids to a certain degree and remineralise the enamel, this protective system of the body is not equal to a constant attack. The longer and the more frequently such an acid attack lasts, the larger the hole in the tooth becomes. A great many factors play a part in the development of caries. Foremost among them is the interplay of certain components of food and acid-forming bacteria. But the composition and quantity of saliva, the duration and frequency of eating, and the composition of the food also have an influence. That leaves only one recommendation: brush thoroughly twice a day and so disturb the process of plaque formation often and thoroughly