What is the FDI notation for the upper right deciduous second molar?

• A. 54
• B. 65
• C. 55
• D. 64

Answer: (C)

FDI notation uses two digits to identify a tooth. The first digit shows the quadrant and dentition: 1–4 are permanent teeth in the four quadrants (upper right, upper left, lower left, lower right), while 5–8 denote the deciduous (primary) teeth in those same quadrants, with 5 corresponding to the upper right. The second digit identifies the tooth’s position within that quadrant, numbered from 1 to 5 in the deciduous set (1 central incisor through 5 second molar). The upper right deciduous second molar sits in the deciduous quadrant of the upper right, and it is the fifth tooth in that quadrant, giving 55. Other options would map to different deciduous teeth in other quadrants or to first molars rather than second molars. Therefore, 55 is the correct notation.