Cavities (tooth decay) occur when the hard outer layer of teeth is broken down.
The teeth are constantly covered in a sticky film of bacteria called plaque. When a person consumes foods or drinks containing sugar, the bacteria in plaque creates acid that then attacks the hard outer layer of the tooth, destroying it over time. Little holes called cavities then form in the tooth.
Toothpaste that contains fluoride strengthens the enamel of the tooth by helping to rebuild enamel that has been attacked by acid, reversing signs of early tooth decay.