9.2.5 The Teeth (Physical Digestion)

• Physical digestion


  Breakdown of food into smaller pieces without chemical change to the food molecules. This happens in the mouth and stomach.
• Physical digestion


  • Increases the surface area of food for the action of enzymes in chemical digestion
• Role of teeth


  They are used for chewing to increase the surface area of the food so that it can be exposed to saliva and other digestive juices and broken down more quickly
• Different types of teeth


  • Incisors - chisel-shaped for biting and cutting
  • Canines - pointed for tearing, holding and biting
  • Premolars and molars - larger, flat surfaces with ridges at the edges for chewing and grinding up food

  
• Crown


  The part of the tooth visible above the gum

  
• Tooth decay


  1. Food is left on the teeth

  2. Bacteria use the sugar (glucose) to respire (anaerobically)

  3. Bacteria convert the sugars into lactic acid

  4. The acid reacts with the enamel

  5. The enamel dissolves

  6. The softer dentine is exposed

  7. If nerves are exposed, pain is felt
• Preventing tooth decay


  • 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)
• How fluoride reduces tooth decay


  • 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