# 53 Human teeth and dental decay

There are four types of teeth in human (incisors, canines, premolars and molars), each specialised for different funtions. 

Position of teeth in the mouth 

Structure of tooth

Causes of dental decay

• Bacteria are present on the surface of our teeth. Food deposits and bacteria form a layer called plaque. Bacteria on the plaque feed on sugars, producing acid. This acid dissolves enamel, forming a hole.

• Dentine underneath the enamel is softer – it dissolves more rapidly.

• If the hole reaches the pulp cavity, bacterial infection can get to the nerve. This results in toothache and possibly, an abscess (an infection in the jaw).

Common misconceptions:

Do not say that sugar causes decay. It only causes problems because of the activity of bacteria feeding on it and producing acids. 

Try this

The outer layer of the crown of a tooth is resistant to attack by bacteria

1. Name this outer layer. (1 mark)
2. State the mineral and the vitamin needed in the diet for the healthy development of this layer. (2 mark)
3. Explain how bacteria can gain entry through this layer into the tooth and cause dental decay. (3 mark)

Answers

1. Enamel
2. Mineral: calcium; vitamin: D
3. Three points from:

• bacteria feed on sugar from food left on the teeth
• bacteria produce acid
• acid attacks or dissolves the enamel
• dentine if softer, so it breaks down more quickly
• this results in a hole in the enamel, exposing the pulp cavity.