Teeth

Introduction

Teeth (singular: tooth) are hard, mineralized structures found in the alveolar arches of the maxilla and mandible. Unlike bone, teeth are not technically part of the skeletal system; they are considered specialized organs of the integumentary system that have evolved for the mechanical breakdown of food (mastication) and to facilitate speech.

Anatomical Structure

A tooth is divided into two primary parts:

Crown: The visible portion of the tooth above the gingival margin.
Root: The portion embedded within the alveolar bone, anchored by the periodontal ligament.
Cervix (Neck): The slight constriction at the junction of the crown and the root (Cementoenamel junction).

Tissue Layers

A tooth is composed of four distinct tissues:

Enamel: The hardest substance in the human body. It is highly mineralized (96% hydroxyapatite) and covers the crown. It is non-vital and cannot regenerate.
Dentin: Located beneath the enamel and cementum. It is a vital, mineralized tissue that contains microscopic dentinal tubules.
Dental pulp: The unmineralized central chamber containing loose connective tissue, blood vessels, and nerves.
Cementum: A bone-like mineralized tissue covering the root surface, providing attachment for the periodontal ligament.

Types of Teeth

Humans are diphyodont, meaning they develop two sets of teeth during their lifetime:

Primary Dentition (Baby Teeth)

**Count**: 20 teeth.
**Composition**: 8 incisors, 4 canines, 8 molars.
**Eruption**: Typically begins at 6 months and is complete by age 3.

Permanent Dentition (Adult Teeth)

**Count**: 32 teeth (including third molars).
**Composition**: 8 incisors, 4 canines, 8 premolars, 12 molars.
**Eruption**: Typically begins at age 6 and concludes in late adolescence.

Dental Notation Systems

To uniquely identify each tooth, clinicians use standardized systems:

Universal Numbering System: Primarily used in the United States (1–32).
FDI World Dental Federation notation: International standard using a two-digit quadrant-based system (e.g., 11, 21, 31, 41).
Palmer notation method: Uses a symbol ($┘, └, ┐, ┌$) representing the quadrant and a number.

Clinical Significance

Dental caries: The demineralization of tooth structure by bacterial acids.
Bruxism: Excessive grinding or clenching that leads to tooth wear (attrition).
Endodontic therapy: Treatment required when the dental pulp becomes infected or necrotic.
Impacted tooth: A tooth that fails to erupt fully into the oral cavity (common with wisdom teeth).