Tap a tooth or search a number to convert between the U.S. Universal system and the FDI/ISO two-digit system commonly encountered in Canada and internationally.
Quick answer: The Universal/National system uses numbers 1–32 for permanent teeth and letters A–T for primary teeth. The FDI/ISO system uses two digits. The first digit identifies the quadrant and dentition; the second identifies the tooth's position from the midline.
Dentists use tooth numbers to identify a specific tooth in charts, treatment plans, referrals, insurance records, and clinical notes. The same physical tooth can have a different label depending on the numbering system being used.
In the Universal system, permanent teeth are numbered 1 through 32. The sequence starts at the patient's upper-right third molar, crosses the upper arch, then continues from the lower-left third molar across the lower arch.
In FDI/ISO notation, permanent quadrants are 1 through 4 and primary quadrants are 5 through 8. The second digit counts outward from the centre of the mouth.
| Feature | Universal / National | FDI / ISO |
|---|---|---|
| Permanent teeth | 1–32 | 11–48 |
| Primary teeth | A–T | 51–85 |
| Structure | Sequential numbering / lettering | Quadrant digit + tooth-position digit |
| Common context | Most commonly used in the United States | International two-digit designation system |
| Tooth | Universal | FDI / ISO |
|---|---|---|
| Upper-right central incisor | #8 | 11 |
| Upper-left central incisor | #9 | 21 |
| Lower-left first molar | #19 | 36 |
| Lower-right first molar | #30 | 46 |
| Upper-right wisdom tooth | #1 | 18 |
| Lower-right wisdom tooth | #32 | 48 |
Primary teeth use a different notation. The Universal system uses letters A through T, while FDI/ISO uses quadrants 5 through 8 with tooth positions 1 through 5.
One detail causes a lot of confusion: right and left describe the patient's right and left. If you are looking at somebody face-to-face, the chart can appear reversed compared with your own perspective.
If a dentist, insurer, referral, or treatment plan gives you a tooth number, use the lookup tool above to convert it and confirm the tooth's location. For treatment decisions, always rely on the notation in your own dental record and confirm any uncertainty with the treating dental professional.
This tooth-numbering tool helps patients and dental teams find the right information quickly. If you run a practice, the same principle applies online: patients need to find the right service, understand what you offer, and know what to do next.
Usually, people using that phrase are referring to FDI/ISO two-digit notation. The formal ISO standard is a two-digit designation system rather than a separate standard named “Canadian.”
The first digit, 3, identifies the permanent lower-left quadrant. The second digit, 6, identifies the first molar. FDI 36 is Universal #19.
Universal #1 is the permanent upper-right third molar, commonly called the upper-right wisdom tooth. Its FDI equivalent is 18.
Universal #8 is the upper-right central incisor. Its FDI/ISO equivalent is 11.
Universal notation uses letters A through T. FDI/ISO uses quadrants 5 through 8 and positions 1 through 5, producing numbers such as 51, 61, 71, and 81 for the primary central incisors.
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