The Anatomy of Teeth and Jaws

A knowledge of the outer shapes and internal details of the teeth and jaws will help the viewer to understand and appreciate the simplyteeth website. We suggest that you familiarise yourself with the information provided. The subjects to be detailed are:

1. The Teeth and Their Parts.
2. Tooth Names and Positions.
3. The Jaws and Jaw Joints (Temporomandibular Joints / TMJ).
4. Dental X-ray Viewing and Interpretation: Seeing Inside Teeth and Bone.

 
1. The Teeth and Their Parts:

• Each tooth has two main parts, the crown and the root.
• The crown and the root meet at the neck of the tooth, which is normally just below the gum margin.

The tooth

Normal teeth, gum and bone

• The crown
  This is the part of the tooth that we see in the mouth.
  It is made up of the enamel, dentine and pulp.
  The appearance of teeth varies in shape and size.
  • The front incisor teeth have a straight edge as a cutting tool.
  • The canine or eye teeth are the pointed long teeth between the incisor and premolar teeth.
  • The pre-molar and molar teeth are larger and have cusps.
  • A cusp is the raised pointed part of the chewing surface of a tooth.
  • The presence of large cusps on pre-molar and molar teeth marks the main difference between them and the front teeth.
  • Pre-molar teeth (bicuspids) have two cusps.
  • Molar teeth each have four or more cusps.
  • The four permanent lower incisor teeth each erupt with three small cuspettes that resemble a serrated edge. These cusps wear down with use and the teeth remain with a straight edge.
  • The four permanent upper incisors may erupt with three very small cuspettes. These are much less obvious than those on the lower incisors. They are also normally worn away to form a straight edge.

• Enamel
  • The enamel is the white hard covering over the crown of the tooth.
  • It is shaped into cusps, fissures and pits in premolar and molar teeth.
  • It is the hardest material in the body and does not have a nerve supply.
    Chipping or damage to enamel only will not be painful.
  • It also does not have a blood supply.
    This results in a chipped tooth remaining exactly as it is.
    Enamel cannot heal or repair as bone or dentine can.

• Dentine
  • Dentine is a cream coloured hard material that makes up the bulk of the tooth.
  • It is covered by enamel on the crown, and by cementum on the roots.
  • The dentine surrounds and protects the nerves and blood vessels (pulp) in the crown and roots.
  • Dentine is alive or vital in as much as more dentine can be formed, and it can register pain.
    • A protective layer of secondary dentine can be layed down over the pulp.
    • This happens in response to caries, attrition, abrasion, erosion, or fracture of a tooth, when the dentine becomes exposed.
    • The tooth becomes sensitive to temperature changes and feels painful, when the dentine is exposed in the above mentioned ways.

• Pulp
  The nerves and blood vessels of the tooth are called the pulp.
  • The pulp occupies the root canals, and the pulp chamber in the crown of the tooth.
  • When it is exposed to infection by decay or injury it will die and cause severe pain. An abscess will develop on the root.
  • The tooth will have to be extracted if a root canal treatment is not performed to save it.

• The roots
  The roots are embedded in the tooth socket in the jaw bone.
  • The front incisor and eye-teeth each have a single root.
  • Pre-molar teeth (bicuspids) have one or two roots.
  • The molar teeth can have two or three roots.
  • Each root has a root canal for the nerves and blood vessels to pass through.
  • Roots are covered by cementum and held in place by the periodontal ligament.

• Cementum
  • The cementum is a thin calcified covering of the roots.
  • It meets the enamel at the neck of the tooth.
  • It has no nerve supply.
  • The cementum covers the dentine of the roots.
  • It is attached to the periodontal ligament.

• Periodontal membrane or ligament
  The periodontal ligament attaches the roots to the alveolar bone of the jaw.
  • It has both a nerve and blood supply
  • The ligament provides an elastic cushion between the tooth and the bone. Slight movement of a tooth is made possible by the ligament.
  • Teeth are not rigidly joined to bone. There is flexibility.

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2. Tooth Names and Positions.

A. Baby Teeth
Tooth Names		Positions
Front Teeth: A. Central incisor B. Lateral incisor C. Canine or eye tooth		Upper Teeth
Back Teeth: D. First molar E. Second molar	Lower Teeth
A. Permanent Teeth
Tooth Names		Positions
Front Teeth: 1. Central incisor 2. Lateral incisor 3. Canine or eye tooth		Upper Teeth
Back Teeth: 4. First premolar 5. Second premolar 6. First Molar 7. Second Molar 8. Third Molar Or Wisdom Tooth	Lower Teeth

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3. The Jaws and Jaw Joints (Temporomandibular Joints / TMJ)

• The temporomandibular joints are the two jaw joints, one at each side of the face.
  • Movement of the lower jaw is made possible by this joint.
  • The upper jaw is called the maxilla and is joined to the temporal bone.
  • The lower jaw is called the mandible or mandibular bone.
  • The term “temporomandibular” refers to the connection between these two bones.
  • Chewing and speech would not be possible without this joint.

Jaw joint (TMJ)

• The TMJ is a variation of a hinge joint. It is technically called a sliding hinge joint. This allows the jaw to be flexible and move in a number of directions:
  • The lower jaw moves up and down when the mouth is opened and closed.
  • When we chew food and speak the jaw movements can be forward and backward, sideways and circular.
  • In young children the jaw only moves up and down like a regular hinge.
  • The flexibility and other movements of the jaw develop with the arrival of the permanent teeth.

Jaw open

Jaw closed

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4. Dental x-ray viewing and interpretation

A dental x-ray is a picture of the inside of a tooth and bone.

• How to read or interpret an X-ray:
  Soft objects appear black, solid objects are white on x-ray.
• What you see as grey/black on x-ray:
  • Decay.
  • Abscess.
  • Nerves and blood vessels (the pulp).
  • Gum in the spaces between teeth.

• What you see as white/cream on x-ray:
  • The enamel.
  • Metal fillings and crowns will be white.
  • The dentine appears as a creamy white colour.
• Bone has a mottled grey and white appearance. It has a fine white line at its margin around the teeth.

Illustration of x-ray showing tooth parts and bone

Abscess above root (the dark area)

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