1 Introduction

The destruction of the mineralised structure of the tooth through the metabolic activities of oral micro-organisms is known as dental caries, and has been described in Chapter 1. Active caries, that is, caries in which there is detectable demineralisation, has been shown to have a pH of 4.9 0.2, but this is arrested by increasing the pH to 5.7 0.5.1 The main acid found to be present in active caries is lactic acid (88.2 8.3%), with minor amounts of acetic (ethanoic) acid (9.6 5.9%).2 Caries in enamel is straightforward, owing to the almost completely inorganic nature of the substrate. In dentine, however, it is more complicated and, in addition to the demineralisation via attack at the inorganic phase, there is destruction of the organic components.2

The classic work on the relationship between sugar and caries was carried out by Stephan, who reported his results in 1940.3 More recent studies have given additional insight into the mechanism of the disease, including the role played by minor acids, such as ethanoic and propanoic.2 It has also been shown that a further feature of dental caries is that the metabolism of sugars causes the oral micro-organisms to form intracellular and extracellular polysaccharides.1 These enable the bacteria to cling tenaciously to the surface of the tooth, and also provide a source of energy for continued metabolic activity.

As part of the preparation of the tooth for repair following the identification of active caries, the affected material needs to be removed. In modern clinical practice, this...