FDI vs Universal vs Palmer tooth numbers

Why there are three systems

Each system grew up in a different place.

• Palmer is the oldest. It comes from a grid idea that the Hungarian dentist Adolf Zsigmondy described in 1861, using Roman numerals for baby teeth.
• The American dentist Corydon Palmer later used letters A to E for baby teeth instead, which made notes easier to read.
• Universal counts every adult tooth once, from 1 to 32. It is the system most dentists in the United States use.
• FDI World Dental Federation notation came later and was made a world standard as ISO 3950. Most countries use it, and so does the World Health Organization.

In Australia, the dental schedule that dentists and health funds share says FDI numbers should be used when a tooth needs to be named. You will mainly meet the other two on documents from the United States or the United Kingdom, or from an overseas clinic.

Sources: Wikipedia, Palmer notation; Universal Numbering System; FDI World Dental Federation notation. the ADA's dental services list, 2022 edition.

How each system counts

FDI

• Pick the quarter first. Adult quarters are 1 upper right, 2 upper left, 3 lower left, 4 lower right.
• Then count from the middle tooth back, 1 to 8.
• Baby teeth use quarters 5 to 8 and positions 1 to 5.

Universal

1. Start at the upper right wisdom tooth as 1.
2. Move along the top to the upper left wisdom tooth, which is 16.
3. Drop to the lower left wisdom tooth, which is 17, and move along the bottom to the lower right wisdom tooth, 32.

Baby teeth are letters, A at the upper right back baby molar round to T at the lower right back baby molar.

Palmer

• Each quarter counts 1 to 8 from the middle, like the second FDI digit.
• A right angle symbol shows the quarter. In typed notes people often write UR, UL, LL or LR instead, so UR6 is the upper right first molar.
• Baby teeth are letters A to E.

Quick conversion rules

You can convert most numbers in your head with these rules.

• FDI 11 to 18: Universal is 9 minus the second digit. So 16 becomes 3.
• FDI 21 to 28: Universal is 8 plus the second digit. So 26 becomes 14.
• FDI 31 to 38: Universal is 25 minus the second digit. So 36 becomes 19.
• FDI 41 to 48: Universal is 24 plus the second digit. So 46 becomes 30.
• Palmer to FDI: swap the letters for the quarter digit. UR is 1, UL is 2, LL is 3, LR is 4. So LR6 is 46.

Two numbers cause most mistakes:

• A Universal 11 is the upper left canine, while an FDI 11 is the upper right front tooth.
• A Universal 21 is a lower left premolar, while an FDI 21 is the upper left front tooth.

When a number is 11 to 32, check which system the document uses before you read it. The interactive chart has a converter that shows all three numbers for any tooth.

Adult conversion table

Baby teeth conversion table

Some Universal charts write baby teeth as 1d to 20d instead of letters. If you see a small d after a number, it is a baby tooth in that style.

Source: Wikipedia, Universal Numbering System.

Which one should you use?

Use the system your dentist uses. In Australia the dental schedule asks for FDI.

• If you have papers from more than one country, write the FDI number next to each tooth before you compare them.
• Then the same tooth has the same name on every page.
• You can ask your dentist about it in their own terms.