The ISO-3950 dental notation system is the international standard notation system defined by the World Health Organization (WHO).

This system is also called the Federation Dentaire Internationale (FDI) notation system as the organization created it, but later it was adopted by the WHO and ISO (International Standard Organization).

It is a two-digit system, and each tooth has two numbers:

• The first number is related to the quadrant in which the tooth is located. The counting starts from the upper right quadrant and goes opposite the clockwise direction.
• The second number is the sequence number of a tooth in the quadrant. The counting starts from the medial incisor and continues to the last molar tooth.