Food is broken down into smaller pieces in the mouth by chewing. This is an example of mechanical digestion. The teeth cut and crush food, and the pieces are mixed with saliva to form a ball of food called a bolus.

There are different types of human teeth, with a different structure and function:

  • incisor – for biting and cutting
  • canine – for holding and cutting
  • premolar and molar - crushing and chewing
Human teeth. Starting at the back there are three pairs of molars, two pairs of premolars,  one pair of canine and two pairs of incisors.

Tooth decay

Tooth decay happens when the hard outer enamel of the tooth is damaged. This can happen when bacteria in the mouth convert sugars into acids that react with the enamel. Bacteria can then enter the softer dentine inside.

Tooth decay can be prevented by:

  • avoiding foods with a high sugar content
  • using toothpaste and drinking water containing fluoride
  • regular, effective brushing to prevent the build-up of plaque (a sticky layer on the teeth)

Fluoride compounds may be added to toothpaste and public water supplies. Fluoride reduces tooth decay by:

  • reducing the ability of bacteria on plaque to produce acid
  • helping to replace calcium ions and phosphate ions lost by tooth enamel because of acid attack

However, there are arguments against fluoridation of drinking water. For example:

  • some people say that they should not be forced to consume fluoride
  • excessive fluoride can cause grey or brown spots on teeth