Definition
Dental plaque is a complex soft non-calcified microbial deposit which accumulates on the surfaces of the teeth. It will also collect on dentures, other appliances in the mouth (e.g. orthodontic braces) and on any rough substance such as a dental filling.

Location
Plaque forms continuously and collects most heavily in those areas, which are sheltered from the friction of eating and tongue movements. It collects particularly around the gum crevice (a natural space between the gum and tooth), especially between the teeth and will be held next to teeth by dentures or orthodontic braces.

Composition
Plaque begins to form within a minute on a cleaned tooth surface. It begins as a film formed from saliva products which stick firmly to the tooth enamel. This film then becomes colonised by bacteria within the saliva. There are approximately 100 million bacteria per ml of saliva and 500 different species present.

The greater the amount of sugar in the diet the greater the amount of plaque formed. This is because some bacteria feed off the sugar and also store it, which makes the plaque bulkier.

Plaque changes over a time period of 1-12 days as different bacteria colonise it. It eventually becomes a tightly packed mass of moving bacteria called a "biofilm". The longer plaque is present, the more harmful the biofilm becomes.

Figure 1. Electron microscopy of the formation of plaque.

Features
In small amounts plaque is not visible to the naked eye (figure 1) but using a harmless pink dye (a type of food dye) can reveal it (figure 2).

Figure 2. Plaque stained using a harmless pink dye.

Thicker plaque is noticeable as yellowish deposits. It will form more rapidly during sleep, as the saliva flow is much reduced so cannot wash off the plaque. In addition when patients are sleeping there is no mechanical action of eating to remove the plaque.

Complications
Plaque commonly becomes mineralised into dental calculus (tartar). Calculus forms both above and below the gum line. It harbours more bacteria, which produce toxins and cause the gums to become inflamed (gingivitis).

Plaque is also a major factor in the cause of dental caries (tooth decay). Certain bacteria in plaque utilise sucrose and produce an acidic environment. These acids destroy the hard tissues of the teeth especially tooth enamel).

Disease Prevention
Plaque needs to be removed daily. It can be removed by using a toothbrush and interdental cleaning aids. Calculus needs to be professionally removed by a dentist or hygienist. Plaque cannot be removed by rinsing with water, using water sprays or eating fibrous foods. Professional assistance is often required for efficient plaque removal.

Plaque removal alone will not prevent dental caries and only a reduction in sugar intake will help to achieve this.