Describe the teeth and gums

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Teeth and Gums: Anatomy

The Tooth

A tooth has two main regions:

Crown — the visible portion above the gum line
Root — the portion submerged below the gum line, anchored in the alveolar bone socket

Layers of the tooth (outermost to innermost):

Layer	Location	Description
Enamel	Covers the crown	The hardest substance in the body; translucent, protects against mechanical and chemical damage
Cementum	Covers the root	Bone-like material that anchors the tooth to the periodontal ligament
Dentin	Beneath enamel/cementum	Denser than bone; forms the bulk of the tooth; exquisitely sensitive to pain when exposed
Pulp	Central core	Soft, myxomatous (gel-like) tissue containing the tooth's blood vessels and nerve supply

Below is a cross-sectional imaging view illustrating the enamel and dentin layers:

Tooth cross-section showing enamel and dentin layers

Multimodality imaging of a tooth cross-section. The outer enamel and inner dentin are clearly distinguishable by their differing optical and absorption properties.

The Gums (Gingivae) and Supporting Structures

The tooth is held in place by the periodontium, a set of supporting structures:

Gingivae (gums) — Soft tissue surrounding and protecting the base of the teeth. Divided into:
- Attached gingiva: A firm collar of tissue just below the crown, tightly bound to the underlying alveolar bone
- Free (unattached) gingiva: A 1–3 mm band that loosely overlaps the base of the crown, creating the gingival sulcus — the shallow groove running along the gum-tooth margin
Alveolar bone — The jaw bone forming the tooth socket
Cementum — Covers the root and serves as an attachment surface
Periodontal ligament — Dense fibrous tissue that tenaciously binds the root's cementum to the alveolar bone, acting as a shock absorber

Summary Diagram

Crown (above gum line)
  └── Enamel (outer protective layer)
      └── Dentin (bulk of tooth)
          └── Pulp (nerves + vessels)

Root (below gum line)
  └── Cementum (outer layer)
      └── Dentin
          └── Pulp

Supporting Structures
  ├── Free gingiva (1–3 mm sulcus at gum-tooth margin)
  ├── Attached gingiva (firm collar below crown)
  ├── Periodontal ligament (binds cementum to bone)
  └── Alveolar bone (tooth socket)

(Harrison's Principles of Internal Medicine, 21st Ed., p. 1082)

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