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M01.02.049 Teeth
Human dentition consists of two sets of teeth:
- Primary dentition (deciduous teeth).
- Permanent dentition (adult teeth).
The teeth are organized into two opposing arches:
- Maxillary (upper) arch.
- Mandibular (lower) arch.
These arches are further divided into left and right halves along the mid-sagittal plane. Teeth are anchored in alveolar sockets and connected to the bone by the periodontal ligament.
Types of Dentition: Primary vs. Permanent
Primary Dentition
- Total Teeth: 20 (10 in each arch, 5 per quadrant).
- Tooth Types in Each Quadrant:
- 2 incisors (central and lateral).
- 1 canine.
- 2 molars.
- Identification: Referred to as letters A to E.
- Eruption Timeline: Begins at 6 months of age.
Permanent Dentition
- Total Teeth: 32 (16 in each arch, 8 per quadrant).
- Tooth Types in Each Quadrant:
- 2 incisors (central and lateral).
- 1 canine.
- 2 premolars.
- 3 molars (including wisdom teeth).
- Identification: Referred to as numbers 1 to 8 (central incisor to wisdom tooth).
- Eruption Timeline:
- Replaces primary teeth starting at 6 years.
- Completes around 13 years, except for wisdom teeth, which erupt in 21 years.
| Feature | Primary Dentition | Permanent Dentition |
|---|---|---|
| Total Teeth | 20 | 32 |
| Quadrants | 4 (5 teeth each) | 4 (8 teeth each) |
| Tooth Types | Incisors, canines, molars | Incisors, canines, premolars, molars |
| Eruption Timeline | 6 months – 3 years | 6 – 21 years |
Tooth Structure
Key Components
- Crown: The visible part of the tooth.
- Enamel: Hard, mineralized covering providing protection.
- Dentino-Enamel Junction (DEJ): Boundary between dentin and enamel.
- Root: Anchors the tooth in the alveolar socket.
- Cementum: Covers the root and connects to the periodontal ligament.
- Cemento-Enamel Junction (CEJ): Where enamel meets cementum.
- Apex: The tip of the root with an apical foramen for blood vessels and nerves.
- Dentin: Lies beneath the enamel and cementum, providing structure.
- Pulp Cavity: Contains nerves and blood vessels.
| Part | Description | Material |
|---|---|---|
| Crown | Visible portion | Enamel |
| Root | Embedded in alveolar bone | Cementum |
| Pulp Cavity | Contains vascular and nerve tissue | Soft tissue |
| Apex | Tip of the root for vascular and neural access | Hard structure |
Types of Teeth
1. Incisors
- Total: 8 (4 maxillary, 4 mandibular).
- Function: Cutting food.
- Clinical Significance: Prone to traumatic injury.
2. Canines
- Total: 4 (2 maxillary, 2 mandibular).
- Function: Piercing and holding food.
- Clinical Significance: Commonly impacted due to dental crowding.
3. Premolars (Only in permanent dentition)
- Total: 8 (4 maxillary, 4 mandibular).
- Function: Crushing and grinding food.
- Clinical Significance: Frequently extracted for orthodontic reasons.
4. Molars
- Primary Dentition: 8 (4 maxillary, 4 mandibular).
- Permanent Dentition: 12 (6 maxillary, 6 mandibular).
- Function: Chewing and grinding food.
- Clinical Significance: Prone to caries due to deep grooves.
| Tooth Type | Number (Primary) | Number (Permanent) | Function |
|---|---|---|---|
| Incisors | 8 | 8 | Cutting food |
| Canines | 4 | 4 | Piercing food |
| Premolars | 0 | 8 | Crushing food |
| Molars | 8 | 12 | Grinding food |
Points to Remember
- Primary Dentition has no premolars.
- Wisdom Teeth (3rd molars) erupt by 21 years.
- Enamel is the hardest tissue but is susceptible to wear and caries.
- The cementum connects teeth to the periodontal ligament.
- Dental trauma and crowding often affect incisors and canines.
Summary
Understanding the structure, types, and clinical significance of human dentition is vital for managing dental issues. For USMLE Step 1, focus on key differences between primary and permanent dentition, tooth anatomy, and developmental timelines.
Bibliography
- OpenStax College. “Dentition Overview.”
- Wikimedia Commons: Primary and Permanent Dentition Illustrations.