Cavity is nothing but demineralisation of the outer most layer of the tooth called enamel, and the second, middle layer called dentin. Food that remains stuck on the tooth is consumed by the bacteria present in our mouth, and an acid is produced as a by product. This acid leads to the decalcification or the demineralisation of the tooth’s enamel and dentin. As a result of which these layers become soft and a cavity is formed. A vicious cycle starts now, leading to the more food lodgement in the cavity and its further progression. If untreated at this stage, the acid reaches the innermost living tissue of the tooth called pulp which contains the nerves and blood vessels, the treatment is now root canal therapy because tooth can no more be saved with a filling.
Prevention is better than cure so filling a tooth at the right time becomes very important to increase the life of the tooth and to avoid root canal treatment which comes at the later stage if tooth is left unattended.