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Tooth numbering system is used by dentists for uniquely identifying and referring to a specific tooth. Over the years, over 20 different teeth numbering systems have been developed. Today, we use the following FDI tooth numbering systems for the numbering of the teeth.

FDI World Dental Federation Two-Digit Notation (International)

This system developed by the Fédération Dentaire Internationale (FDI), World Dental Federation notation is also known as ISO-3950 notation. The human teeth are symmetrically arranged in the mouth. Each quadrant of the mouth has 8 different teeth that are mirrored horizontally and vertically to the other quadrants.

In the FDI (Fédération Dentaire Internationale) World Dental Federation notation each one of these 8 teeth is assigned a number from 1 to 8, starting from the center front tooth (central incisor) and moving backwards up to the third molar (number 8). Each quadrant is also assigned a number, from 1 to 4 for the adult (permanent) teeth or 5 to 8 for the baby (primary or deciduous) teeth.

The combination of these two numbers (Quadrant code number & Tooth code number) specifies how are teeth numbered. This tooth numbering system is called, the Two-Digit World Dental Federation Notation or FDI notation system.