Dental plaque or biofilm is highly organised community of microorganisms, which grow on the surface of teeth. The presence of certain quantity of plaque on the teeth is perfectly normal and the substances it produces are neutralized by saliva, but in the case of excessive plaque accumulation it causes damage to teeth, gums and bone.
Plaque produces for example acids that can etch away the tooth tissues which exhibits itself as dental caries. Another toxic substances from plaque harm gums and bone and cause their inflammation.
You can see that the plaque grows preferably on portion of the teeth which neighbors the gum, in the inter-dental spaces and in pits and fissures. When blowing air on the teeth, we can see that the plaque does not grow under the gum line, but in cases of severe gum inflammation (chronic periodontal disease) when the root surface is covered with calculus, the plaque can grow deep under the gum line.
There is high concentraion of acids in the closed inter-dental spaces which are filled with plaque and thus the caries forms on the lateral wall of teeth (approximal caries). If the plaque is efectively removed, the forming of these approximal caries can be prevented.