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Dental AnatomyBasic

FDI notation: how teeth are numbered

Each tooth is named with 2 digits: the first tells you the quadrant and the second, the position counting from the midline.
A real human skull. In the permanent dentition there are up to 8 teeth per quadrant: 2 incisors, 1 canine, 2 premolars and 3 molars.
A real human skull. In the permanent dentition there are up to 8 teeth per quadrant: 2 incisors, 1 canine, 2 premolars and 3 molars.Photo: Grey Geezer (crop: MagentaGreen) · CC BY-SA 4.0, Wikimedia Commons

What you need to know

  • Permanent quadrants 1 to 4, clockwise, as seen when facing the patient: 1 upper right, 2 upper left, 3 lower left, 4 lower right.
  • Positions 1 to 8: 1 central incisor, 2 lateral incisor, 3 canine, 4 first premolar, 5 second premolar, 6 first molar, 7 second molar, 8 third molar.
  • Primary (baby) teeth: quadrants 5 to 8, in the same order, and positions 1 to 5. There are no premolars.
  • It's read digit by digit: 36 is “three, six”, not “thirty-six”.

Terms in plain words

QuadrantEach quarter of the mouth: upper or lower, and the patient's right or left (not yours).
MidlineThe imaginary line that runs between the two central incisors.
Primary dentitionThe 20 baby teeth.

For the exam

Which tooth is 75?

Show answerHide answer

Lower left second primary molar: quadrant 7 (lower left, primary) and position 5.

Sources

  1. FDI World Dental Federation: two-digit system, adopted as the ISO 3950 standard.
  2. Enhancing Precision: Proposed Revision of FDI's 2-Digit Dental Numbering System (describes the current system). View source
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