Teeth: Structure, Types, Functions, and Dental Formula

This note provides a detailed and intuitive understanding of the human tooth, covering its intricate structure, the different types of teeth and their specific functions, and the dental formula of an adult, as outlined in the syllabus.

1. Structure of a Tooth

A tooth is a complex biological structure designed for mastication (chewing) and plays a vital role in speech and facial aesthetics. It is composed of several distinct parts, each with a specialized function.

1.1 Main Anatomical Parts

• Crown: The visible part of the tooth that protrudes above the gum line. It is covered by enamel and is the primary surface for chewing.
• Neck (Cervix): The narrow region where the crown meets the root, typically located at the gum line.
• Root: The portion of the tooth embedded within the jawbone. It anchors the tooth firmly in place and is not visible under normal circumstances.

1.2 Layers of a Tooth

• Enamel:
  • Description: The outermost layer of the crown, and the hardest substance in the human body. It is primarily composed of hydroxyapatite crystals.
  • Function: Provides a durable, protective covering for the crown, shielding the tooth from physical wear, chemical erosion (from acids), and bacterial invasion. It allows for efficient chewing and biting.
• Dentin:
  • Description: A yellowish, bone-like material that lies beneath the enamel in the crown and beneath the cementum in the root. It makes up the bulk of the tooth structure and contains microscopic tubules that transmit sensations.
  • Function: Provides support to the enamel and protects the pulp. It is sensitive to temperature changes and pressure, and its exposure can lead to tooth sensitivity or pain.
• Cementum:
  • Description: A specialized calcified substance that covers the root of the tooth. It is softer than enamel and dentin but is crucial for tooth stability.
  • Function: Along with the periodontal ligament, it helps to firmly anchor the tooth to the alveolar bone (jawbone). It also protects the root surface.
• Pulp:
  • Description: The innermost part of the tooth, located in the pulp chamber (in the crown) and root canals (in the root). It is a soft tissue containing blood vessels, nerves, and connective tissue.
  • Function: Provides nourishment to the dentin, supplies sensation (e.g., to pain, temperature, pressure), and plays a role in the formation of dentin throughout the tooth's life.

1.3 Supporting Structures

• Periodontal Ligament (PDL): A group of specialized connective tissue fibers that attach the cementum of the tooth root to the alveolar bone. It acts as a shock absorber during chewing.
• Gingiva (Gums): The soft tissue that surrounds the teeth and covers the alveolar bone. It provides a protective seal around the teeth, preventing bacteria from entering the deeper structures.
• Alveolar Bone: The part of the jawbone that contains the tooth sockets and supports the roots of the teeth.

2. Functions of Different Types of Teeth

Humans typically have two sets of teeth: deciduous (baby) teeth and permanent teeth. An adult typically has 32 permanent teeth, categorized into four main types, each with a specialized function:

• Incisors (8 teeth):
  • Location: The four front teeth in both the upper and lower jaws.
  • Appearance: Chisel-shaped with a sharp, flat biting edge.
  • Function: Primarily used for cutting and biting off pieces of food. They also play a role in speech articulation and supporting the lips.
• Canines (4 teeth):
  • Location: One on each side of the incisors in both the upper and lower jaws.
  • Appearance: Pointed and cone-shaped, resembling a dog's canine teeth.
  • Function: Designed for tearing and piercing tough foods. They are the longest teeth and help guide the jaw during chewing.
• Premolars (Bicuspids) (8 teeth):
  • Location: Two on each side behind the canines in both the upper and lower jaws.
  • Appearance: Have two cusps (points) on their chewing surface.
  • Function: A transitional tooth type, used for both tearing and crushing food. They help in grinding food into smaller pieces before it reaches the molars.
• Molars (12 teeth):
  • Location: The rearmost teeth in the mouth, typically three on each side in both the upper and lower jaws (including wisdom teeth).
  • Appearance: Large, broad, and flat chewing surfaces with multiple cusps.
  • Function: Primarily responsible for grinding and mashing food into a fine pulp, making it easier to swallow and digest. They exert the most force during chewing.

3. Dental Formula of an Adult

The dental formula is a concise way to represent the number of each type of tooth in one half of the upper and lower jaws. For an adult human with a full set of permanent teeth, the dental formula is:

2(I 2/2, C 1/1, PM 2/2, M 3/3) = 32

Let's break down this formula:

• 2: This indicates that the formula represents one half of the mouth, and the total number of teeth is obtained by multiplying the sum of teeth in one half by two (for both sides of the mouth).
• I 2/2: Refers to Incisors. There are 2 incisors in the upper half-jaw and 2 incisors in the lower half-jaw.
• C 1/1: Refers to Canines. There is 1 canine in the upper half-jaw and 1 canine in the lower half-jaw.
• PM 2/2: Refers to Premolars. There are 2 premolars in the upper half-jaw and 2 premolars in the lower half-jaw.
• M 3/3: Refers to Molars. There are 3 molars in the upper half-jaw and 3 molars in the lower half-jaw.

Calculation: (2 Incisors + 1 Canine + 2 Premolars + 3 Molars) in upper half = 8 teeth (2 Incisors + 1 Canine + 2 Premolars + 3 Molars) in lower half = 8 teeth

Total teeth in one half of the mouth = 8 (upper) + 8 (lower) = 16 teeth Total teeth in the entire mouth = 16 teeth * 2 = 32 teeth

This formula represents a complete set of permanent teeth, including the third molars (wisdom teeth), which may or may not erupt in all individuals.