Dentists rely on standardized numbering systems to communicate precisely about a patient’s teeth. The human mouth contains up to 32 permanent teeth, and using a unique number or code avoids the ambiguity of common names like “back molar” or “front tooth.” This specificity is necessary for all aspects of dental care, including restorative work, orthodontics, and insurance claims. Two primary methods exist globally, ensuring that dental professionals can accurately understand records from any location.
The Universal Numbering System
The Universal Numbering System (UNS) is the standard method adopted by the American Dental Association. This system assigns a unique number from 1 to 32 to each permanent tooth, creating a continuous sequence throughout the entire mouth. Numbering begins with the upper right third molar (wisdom tooth), designated as tooth number 1.
The count proceeds sequentially across the upper jaw toward the patient’s left side, ending with the upper left third molar (number 16). It then drops to the lower jaw, starting with the lower left third molar (number 17). Numbering continues across the mandibular arch, moving from the left side to the right side, concluding with the lower right third molar (number 32).
This system effectively divides the mouth into four quadrants. For example, the four central incisors are numbers 8 and 9 on the top and 24 and 25 on the bottom. Even if a tooth is missing, its assigned number is reserved, ensuring the overall chart remains consistent.
The FDI World Dental Federation System
Internationally, the most common method is the FDI World Dental Federation System, also known as ISO 3950 notation. This system uses a two-digit code to identify each permanent tooth. The first digit specifies the quadrant of the mouth where the tooth is located.
Quadrants are numbered 1 through 4, starting with the upper right side (1) and moving clockwise to the upper left (2), the lower left (3), and the lower right (4). The second digit indicates the specific tooth’s position within that quadrant, counting from the midline outward (1 being the central incisor, up to 8 being the third molar).
For example, the number 11 refers to the upper right central incisor (quadrant 1, position 1). The number 36 identifies the lower left first molar (quadrant 3, position 6). This two-digit structure contrasts with the Universal System’s continuous count and makes the system highly efficient for record sharing among dentists worldwide.
How Dentists Number Primary Teeth
Both the Universal and FDI systems adapt their methods to number the 20 primary teeth present in a child’s mouth. The Universal System uses capital letters instead of numbers. The sequence begins with the upper right second molar, designated ‘A’, and proceeds clockwise.
The count continues across the upper jaw to the upper left second molar, labeled ‘J’. It then drops to the lower jaw, starting with the lower left second molar, ‘K’, and ends at the lower right second molar, ‘T’.
The FDI system modifies its quadrant numbering for primary teeth. Quadrants are numbered 5 through 8, following the same clockwise pattern as the permanent system: upper right (5), upper left (6), lower left (7), and lower right (8).
The second digit in the FDI code only runs from 1 to 5 because primary dentition lacks premolars and third molars. For example, the primary upper right central incisor is labeled 51, and the primary lower left second molar is labeled 75.