Dental caries is a process which may take place on any tooth surface in the oral cavity where a microbial biofilm (dental plaque) is allowed to develop for a period of time. Although there are some 300 bacterial species in dental plaque, it is not a haphazard collection of micro-organisms. It is an ordered accumulation forming a community with a collective physiology. The bacteria in the biofilm are always metabolically active, causing minute fluctuations in pH. These may cause a net loss of mineral from the tooth when the pH is dropping. This is called demineralization. Alternatively there may be a net gain of mineral when the pH is increasing. This is called remineralization. The cumulative result of these de- and remineralization processes may be a net loss of mineral and a carious lesion which can be seen. Alternatively the changes may be so slight that a carious lesion never becomes apparent