Anatomy

Every tooth consists of a crown and one or more roots. The crown is the part visible in the mouth and the roots are hidden inside the jaw, the junction of the crown and root is called the neck and the end of the root is the apex

Composition of a tooth

Enamel

Enamel is the protective outer covering of the crown and is the hardest substance in the body

It is made up of 96% mineral crystals (inorganic) arranged as prisms in an organic matrix called the interprismatic substance

The main mineral crystals are hydroxyapatite

The prisms lie at right angles to the junction with the next tooth layer (dentine)

The junction between these two layers is known as the Amelodentinal junction (ADJ)

Enamel is formed before tooth eruption by ameloblast cells which lie at the ADJ

It contains no nerves or blood vessels and cannot experience any pain

It can not grow or repair itself so any damage is permanent, it can however remineralise its surface after an acid attackCan exchange fluoride to form crystals which make the surface harder and more resistant to acid attack

Is translucent in appearance

Dentine

Forms the bulk of the tooth and is covered by the enamel in the crown of the tooth and by cementum in the root of the tooth

It consists of upto 80% inorganic tissue, mainly calcium

It is composed of hollow tubes which contain nerve endings called fibrils

It is a living tissue so therefore can feel painSofter than enamel and has a shock absorbing capability

Dentine is formed by Odontoblast cells and these lie along the the inner edge of the pulp chamber and can produce new dentine as required

It can repair itself to an extent by laying down secondary dentine

Secondary dentine also forms as part of a natural ageing process and its formation gradually narrows the pulp chamber

Dentine is a yellowish colour and gives teeth their shade

Pulp

The pulp is a soft tissue and is found at the very centre of the tooth in both the crown and root

Contains nerves and blood vessels, it allows the tooth to feel pain sensations

The nerves and blood supply enter the pulp through the apical foramen at the apex of the tooth

Cementum

Cementum is the protective outer covering of the root

It meets enamel at the neck of the tooth and lies beneath the gingivae

It allows the attachment of the tooth root to the supporting structure of the periodontal ligament

Softer than dentine

Paler than dentine and darkens with age

Formed by cells called cementoblasts

Supporting structures

The supporting structures can be found around the roots of the teeth and they hold the teeth in their sockets.

The hold is not rigid, it allows the teeth to have some movement which acts as a shock absorber when pressure is exerted on the teeth by chewing

Periodontal ligament

The periodontal ligament is a fibrous tissue that attaches the teeth to the alveolar bone and surrounding gingivae

It acts as a shock absorber to teeth during chewing

Its fibres are made up of a protein called collagen

They run in various directions which allows the teeth to move in their sockets

This prevents tooth fracture and pain when forces are exerted on the teeth such as chewing

Inflammation of the ligament is called periodontitus and occurs during periodontal disease

Alveolar Bone

The maxilla and mandible both contain a horse shoe shaped ridge of bone called the alveolar process

It is here that teeth form and then from where they erupt into the mouth

Is a specialised bone found only in the jaws

The outer layer is made of a hard compact bone called the lamina dura

The inner layer is called cancellous bone and is sponge like in appearance to allow the passage of nerves and blood vessels that supply the jaws, teeth and the surrounding soft tissues

The purpose of the alveolar bone is to support the teeth, and when a tooth is extracted the bone gradually resorbs away

The teeth lie in individual sockets in the alveolar bone, each one being lined with the lamina dura

The outer surface of the alveolar bone is covered in specialised alveolar mucosa which forms the gingivae around the necks of the teeth

Gingiva

This is the correct term for the gums, it is a specialised soft tissue that is only found in the oral cavity.

It is attached to the alveolar bone as a mucoperiosteal layer of tissue

The gingivae fits around the neck of every tooth like a tight cuff this site is called the junctional epithelium

The gingival crevice is a shallow space between the tooth surface and gingival margin

A mound of gingival tissue occurs between each tooth this is called the interdental papilla

When healthy the gingivae are firm, pink and have a stippled appearance

Inflammation of the gingivae is called gingivitis caused by plaque, gingivae appears red and swollen and bleeds easily

The gingiva can be forced to overgrow and become hyperplastic due to medication patients may be taking