Basic Tooth Anatomy
Teeth are formed in two parts. The crown, which is the white part you can see when you smile; and the roots, which remain under the gum and hold the tooth in place. Each tooth sits in a socket (hole) within the jawbone.
Teeth start to develop under the gum before they erupt (come through the gum). The crown forms first and then the roots. The root continues to develop up until about 3 years after the tooth has erupted!
The tooth itself is made up of four different types of tissue:
- Enamel
This is the outermost, white layer around the crowns of our teeth. Enamel is the hardest substance in the human body - it's even harder than our bones! It is mainly made up of a mineral called hydroxyapatite.
Enamel is formed by special cells called "ameloblasts" but these are only present whilst the tooth is developing under the gum. This means once enamel is lost, through decay or tooth wear, it cannot be regrown.
- Dentine
This is the middle, yellow-ish layer of our teeth. There is much less mineral in dentine so it is not as hard as enamel.
Dentine is made up of lots of tiny fluid-filled tubes ("tubules") that run from the enamel to the pulp (nerve).
Dentine is laid down by special cells called "odontoblasts" which sit along the border of the dentine and pulp. There are three types of dentine:
- primary dentine which is laid down before the tooth is fully formed
- secondary dentine which continues to form throughout our lives
- tertiary dentine, also known as "reactive dentine", is formed very quickly to try to protect the nerve from damage - for example, when there is deep tooth decay.
- Pulp
This is the innermost layer of our teeth where the nerve and blood supply of the tooth sits. The pulp runs from the pulp chamber in the crown to the tips of the root under the gum. The "root canal" is the space where the pulp sits within the root of the tooth.
Its main role is in providing nutrition and formation of dentine and defence against bacterial invasion.
- Cementum
This is the outermost layer of the roots of our teeth and covers the dentine. Cementum is not usually seen unless the gum has receded (worn or shrunk away).
A special tissue called the "periodontal ligament" attaches the cementum to the bone and holds the tooth in place. The periodontal ligament is a spongy layer and allows for very slight tooth movement within the bone.