What Do Tooth Numbers Mean?

Often when I see patients they ask me “I was told I need a procedure done on a tooth -but I can’t figure out which tooth they meant- what is tooth number 15?” Tooth “15” means an upper right premolar – but as a patient you can be forgiven for not knowing.

Here is a very quick introduction to tooth numbering, and some useful simple diagrams to help you.

There are two systems of tooth numbering that you may need to be aware of.

Tooth Numbers Around The World (Except the U.S.)

The ISO Standard – Pretty Much Everywhere

In Australia, the U.K., and much of the world we use the ISO standard – which was adapted by the World Health Organisation(WHO) from a previous widely used system. Most dental research uses this numbering. In this system the mouth is split into four quadrants. Upper right and upper left, lower right and lower left.

In this system the numbers represent the teeth listed below

The ISO Standard Universal Tooth Numbers

  • 11, 12, 21, 22 – Are Upper Incisors
  • 13, 23 – Are Upper Canines
  • 14, 15, 24, 25 – Are Upper Premolars
  • 16, 17, 18, 26, 27, 28 – Are Upper Molars
  • 31, 32, 41, 42 – Are Lower Incisors
  • 33, 43 – Are Lower Canines
  • 34, 35, 44, 45 – Are Lower Premolars
  • 36, 37, 38, 46, 47, 48 – Are Lower Molars

What about baby teeth?

For baby teeth (the ‘deciduous’ dentition) we use a similar system with the baby teeth split into quadrants. Because the baby teeth are often present at the same time as adult teeth – we give each quadrant a different number. Number 5, 6, 7, and 8.

Primary or Baby teeth are also split into quadrants for numbering.

For the baby teeth numbers

  • 51, 52, 61, 62 are Upper Baby Incisors
  • 53 and 63 are Upper Baby Canines
  • 54, 55, 64, 65 are Upper Baby Molars
  • 71, 72, 81, 82 are Lower Baby Incisors
  • 73 and 83 are Lower Baby Canines
  • 74, 74, 84, 85 are  Lower Baby Molars

American Tooth Numbering

Often in the U.S. teeth are numbered from right to left, upper to lower, teeth are numbered consecutively. Think of it like the metric system – the scientific community and most of the world use metric/ISO tooth numbering – and the U.S. uses imperial/American tooth numbering.

American Tooth Numbering

Please comment below if you have any further questions about tooth numbering.


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