An extracted tooth has been sectioned to show three different carious lesions and the direction of penetration of the advancing caries. Note the two stages of the occlusal lesions. On the left the caries has only just penetrated through the fissure and entered the dentine, clearly preceded by the translucent zone. On the right the pulp is now almost involved. The penetration by the caries is twice as deep as it is wide and has followed the direction of the dentinal tubules with a degree of lateral spread, limited to some extent by the mineralisation of the lateral canals. The proximal lesion on the left has entered the enamel on a narrow front and then progressed inwards and downwards along the path of the dentinal tubules, again preceded by the translucent zone. This pattern of attack for all lesions is significant in the design of cavities that are intended to remove caries only and minimize the loss of further tooth structure. Note that only grossly softened dentine should be regarded as caries and not reversible. Colour is not significant and the lower layers of softened dentine will generally be remineralisable.