Anatomy and Numbering Systems of Human Teeth

Gingival Anatomy

The health of the supporting tissues is assessed through specific gingival landmarks:

• Marginal Gingiva (Free Gingiva): The "collar" of tissue at the edge of the gum nearest the tooth.
• Sulcus: The space between the tooth surface and the unattached marginal gingiva.
• Interdental Papilla: The part of the unattached gingiva that fills the space between two teeth.
• Attached Gingiva: The zone of firm, keratinized (tough) tissue bound to the underlying bone.
• Alveolar Mucosa: The movable, non-keratinized, often redder tissue that covers the alveolar bone.
• Mucogingival Junction: The scalloped line that separates the attached gingiva from the alveolar mucosa.

Tooth Types and Functions

Humans are heterodont, meaning we possess different types of teeth shaped for different functions.

Anterior Teeth

The anterior teeth are located at the front of the mouth and include the incisors and canines.

• Incisors: These are single-rooted teeth with sharp, thin edges designed for cutting or making an "incision". Their lingual surface is often shovel-shaped to guide food into the mouth.
• Canines (Cuspids): Located at the "corners" of the dental arch, canines are the longest teeth in the mouth, possessing the longest roots. Because of their sturdy structure, they are known as the "cornerstones" of the dental arch and are used for tearing food.

Posterior Teeth

The posterior teeth are located behind the canines and include the premolars and molars.

• Premolars (Bicuspids): These teeth act as a bridge between canines and molars. They typically feature two cusps: a pointed buccal cusp for holding food and a lingual cusp for grinding.
• Molars: These are the largest teeth, usually featuring four or more cusps. Their primary function is the heavy grinding of food.

Dentition Stages

Human dental development follows a specific sequence involving three distinct stages:

1. Primary Dentition (Baby Teeth/Deciduous Teeth): This is the first set of 20 teeth. It consists of 8 incisors, 4 canines, and 8 molars. Notably, primary dentition does not include premolars.
2. Mixed Dentition: A transitional period, typically occurring between ages 6 and 12, where both primary and permanent teeth are present in the mouth. This stage begins with the eruption of the first permanent tooth (usually the mandibular first molar) and ends when the last primary tooth is shed.
3. Permanent Dentition (Adult Teeth): The final set of 32 teeth. This stage begins once the last primary tooth has been shed.

Succedaneous vs. Non-Succedaneous

A critical concept in clinical identification is whether a permanent tooth replaces a primary tooth:

• Succedaneous Teeth: Permanent teeth that replace primary teeth (incisors, canines, and premolars).
• Non-Succedaneous Teeth: Permanent teeth that do not replace any primary teeth (the permanent molars).

Tooth Anatomy and Surfaces

Structural Divisions

A tooth is composed of two main parts: the crown and the root.

• The Crown is covered by enamel, the hardest tissue in the body.
• The Root is covered by cementum.
• The Cementoenamel Junction (CEJ) is the line where the enamel of the crown meets the cementum of the root.

Clinical vs. Anatomical Distinction It is vital to distinguish between anatomical and clinical structures. The anatomical crown and root refer to the physical extent of the enamel and cementum, which never changes. However, the clinical crown is only the portion of the tooth visible in the mouth, and the clinical root is the portion hidden beneath the gingival tissues.

Tooth Surfaces

To describe the location of decay or anatomy, clinicians use specific directional terms based on the tooth's relationship to surrounding structures:

• Facial/Labial/Buccal: Surfaces facing the lips (labial) or cheeks (buccal).
• Lingual/Palatal: Surfaces facing the tongue (lingual) or the palate (palatal).
• Mesial: The surface closest to the midline.
• Distal: The surface furthest from the midline.
• Proximal: A general term for the side surfaces of a tooth (mesial and distal).
• Occlusal/Incisal: The biting surface. "Occlusal" is used for posterior teeth, while "incisal" is used for anterior teeth.

Dividing the Tooth

Teeth are divided into thirds for precise description:

• Horizontally (Root): Apical third (near the tip), middle third, and cervical third (near the neck).
• Horizontally (Crown): Incisal/Occlusal third, middle third, and cervical third.
• Vertically (Crown): Mesial third, middle third, and distal third.

Tooth Numbering Systems

To identify a specific tooth, a clinician must specify the dentition, the arch (maxillary/upper or mandibular/lower), the quadrant, and the tooth type.

1. Universal/National System

Commonly used in the United States:

• Permanent Teeth: Numbered 1–32, starting from the maxillary right third molar and moving around the arch to the mandibular right third molar.
• Primary Teeth: Labeled with letters A–T, starting from the maxillary right second molar.

2. ISO/FDI System

The international standard and the predominant system used in Canadian clinics:

• It uses a two-digit system. The first digit represents the quadrant, and the second represents the tooth's position from the midline.
• Permanent Quadrants: 1 (Maxillary Right), 2 (Maxillary Left), 3 (Mandibular Left), 4 (Mandibular Right).
• Primary Quadrants: 5 (Maxillary Right), 6 (Maxillary Left), 7 (Mandibular Left), 8 (Mandibular Right).

3. Palmer Notation

This system uses a quadrant symbol (a vertical and horizontal line forming a bracket):

• Permanent Teeth: Numbered 1–8 in each quadrant, starting from the central incisor.
• Primary Teeth: Labeled A–E in each quadrant, starting from the central incisor.

Exam Tip: Identifying a Tooth If asked to identify a tooth, always follow this hierarchy:

1. Dentition (Primary or Permanent?)
2. Arch (Maxillary or Mandibular?)
3. Quadrant (1, 2, 3, or 4?)
4. Tooth Type (Incisor, Canine, etc.).