CorpusHuman Anatomy

Tooth: Molar in Longitudinal Section

Mandibular first molar in its socket, with periodontium and neurovascular supply

A two-rooted mandibular molar cut lengthways (mesial root on the left, distal root on the right). The crown above the gum is capped by enamel, the hardest tissue in the body (about 96% hydroxyapatite). Below the enamel, dentin forms the bulk of the tooth; its tubules (fine lines) run out from the pulp. The pulp chamber, with horns under the cusps, continues as a root canal in each root and opens at the apical foramen. At the neck (cemento-enamel junction) the enamel ends and cementum begins, covering the roots.

The tooth is slung in its bony socket by the periodontal ligament, a fibrous joint called a gomphosis, against the thin cortical lining of the socket (lamina dura). Spongy alveolar bone of the mandible lies around it. The gingiva cuffs the neck and leaves a shallow gingival sulcus. The inferior alveolar nerve, artery and vein (from V3 and the maxillary artery) run in the mandibular canal and send branches up through each apical foramen into the pulp. The animation shows blood flowing into the pulp and pain impulses leaving it.

Step-by-step

  1. Crown, neck and root

    The enamel-covered crown meets the cementum-covered root at the neck (cemento-enamel junction). This molar has two roots joined at the furcation.

  2. Enamel

    About 96% hydroxyapatite arranged in rods. It is acellular and avascular, and because ameloblasts are lost at eruption it cannot regenerate. It is thickest (about 2–2.5 mm) over the cusps.

  3. Dentin

    About 70% mineral and forms the bulk of the tooth. Odontoblast processes in its tubules make it living and sensitive, and secondary and reparative dentin keep being added throughout life.

  4. Pulp, root canals and apical foramen

    Loose connective tissue with odontoblasts, vessels and nerves fills the pulp chamber and root canals and communicates with the periapical tissues through the apical foramen. Pulpal inflammation is painful because the pulp is enclosed in rigid dentin.

  5. Cementum and periodontal ligament

    Cementum anchors collagen fibres of the periodontal ligament (Sharpey fibres), which suspend the tooth in its socket: a gomphosis that absorbs chewing forces and senses bite pressure.

  6. Alveolar bone

    The alveolar process of the mandible forms the socket. Its thin cortical lining (lamina dura) is backed by spongy bone. It resorbs once the teeth are lost.

  7. Gingiva and sulcus

    Keratinised masticatory mucosa cuffs the neck. The gingival sulcus (3 mm or less in health) is where plaque-induced gingivitis and periodontitis begin.

  8. Nerve and blood supply

    Branches of the inferior alveolar nerve (V3) and of the inferior alveolar artery and vein, which run in the mandibular canal, enter each apical foramen. The inferior alveolar nerve block anaesthetises all the lower teeth on that side.

Labelled parts