FDI tooth numbering on lab prescriptions: a quick guide for Canadian practices
FDI notation names each tooth with two digits, the quadrant and the position. Here is how to read it, write it on a lab Rx and avoid mix-ups.
By the Tusko team
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FDI notation names every tooth with two digits. The first digit is the quadrant of the mouth, and the second is the tooth’s position, counted from the midline.
It is the system in common use in Canada, and it is set out in ISO 3950. On a lab Rx, write it as “tooth 11”.
The rest of this guide covers how to read the two digits, how to write them, and where mix-ups with other systems happen.
The FDI chart, as you face the patient
The FDI chart of the 32 permanent teeth in four quadrants, with the patient’s right on the left. Tooth 11, the upper right central incisor, and tooth 36, the lower left first molar, are picked out.
- Tooth 11: Quadrant 1, position 1: the upper right central incisor
- Tooth 36: Quadrant 3, position 6: the lower left first molar
The first digit is the quadrant
Quadrants are numbered clockwise as you look at the patient, starting at the patient’s upper right.
| Quadrant | Where it is | Permanent teeth | Primary teeth |
|---|---|---|---|
| Upper right | The patient’s right, top | 1 | 5 |
| Upper left | The patient’s left, top | 2 | 6 |
| Lower left | The patient’s left, bottom | 3 | 7 |
| Lower right | The patient’s right, bottom | 4 | 8 |
Left and right always mean the patient’s. On a screen or a model facing you, the patient’s right is on your left.
The second digit is the position
Positions count outward from the midline, from 1 at the front to 8 at the back.
| Position | Permanent tooth |
|---|---|
| 1 | Central incisor |
| 2 | Lateral incisor |
| 3 | Canine |
| 4 | First premolar |
| 5 | Second premolar |
| 6 | First molar |
| 7 | Second molar |
| 8 | Third molar |
Put the two digits together and you have the tooth. Tooth 36 is quadrant 3, position 6: the lower left first molar.
Primary teeth have five positions in each quadrant. Tooth 51 is the upper right primary central incisor, and tooth 85 is the lower right primary second molar.
How to say it and write it
Say the digits separately. Tooth 11 is “one one”, and tooth 46 is “four six”.
Reading it as “eleven” or “forty-six” hides the fact that the number is two pieces of information.
On an Rx, write the word “tooth” before the number. A bare 11 can be read in another system, and “tooth 11” on a form marked FDI cannot.
For a bridge, name every tooth involved and say which are abutments. “Bridge, teeth 13 to 23, pontics at 11 and 21” leaves nothing to work out.
For an implant, name the site the same way. “Implant crown, tooth 36” tells the lab the position even though no tooth is there.
Three examples
- A single crown. “Zirconia crown, tooth 46” names the lower right first molar.
- A bridge. “Three-unit bridge, teeth 24 to 26, pontic at 25” names two abutments and the tooth being replaced.
- A child’s appliance. “Space maintainer, tooth 85 lost” names a lower right primary second molar.
On a digital Rx, the tooth is often picked from a chart and never typed. Check which system that chart is drawn in, and that the picked tooth shows its number.
FDI and Universal side by side
The Universal system is the one in common use in the United States. It numbers permanent teeth from 1 to 32 in one loop.
The loop starts at the upper right third molar, runs across the top, drops to the lower left and comes back along the bottom.
The same tooth has a different number in each system. These are some that turn up on prescriptions every week.
| Tooth | FDI | Universal |
|---|---|---|
| Upper right first molar | 16 | 3 |
| Upper right canine | 13 | 6 |
| Upper right central incisor | 11 | 8 |
| Upper left central incisor | 21 | 9 |
| Upper left canine | 23 | 11 |
| Upper left first molar | 26 | 14 |
| Lower left first molar | 36 | 19 |
| Lower left canine | 33 | 22 |
| Lower right canine | 43 | 27 |
| Lower right first molar | 46 | 30 |
Look at the number 11 in that table. It is an upper right central incisor in FDI and an upper left canine in Universal.
Eighteen numbers exist in both systems, including 11 to 18 and 21 to 28, and each means a different tooth. That overlap is where a crown gets made for the wrong tooth.
Where mix-ups happen
A numbering error is rarely a lapse of knowledge. It comes from two systems meeting without anyone noticing.
- Scanner and design software. Many products can show either system. A default set for the United States will show Universal numbers.
- A lab in another country. A US lab may read your 21 as a lower left premolar unless the Rx says FDI.
- New team members. Someone trained elsewhere may write the system they learned.
- Old paper forms. A printed lab slip with a tooth chart may be numbered in a system nobody chose.
- Left and right. A note written from the dentist’s point of view flips the quadrant.
Each one is easy to rule out once. Check your scanner’s setting, and ask every lab you use which system its forms and software show.
A short check for every Rx
Four habits make a tooth number hard to misread.
- Write “tooth” before every number
- State the system once on the form, as FDI
- Check that the number on the Rx matches the tooth prepared in the scan
- For a bridge or implant, name every site and its role
The third item catches an error that is costly to fix. A lab that sees a preparation on one tooth and a different number on the Rx will stop and ask.
Our dental lab prescription checklist covers the rest of what a complete Rx needs.
Why it matters between a practice and a lab
A tooth number is the one field on an Rx with no room for interpretation. Shade can be discussed, and a number is either right or wrong.
A wrong one costs a remake and a second appointment. The fix is one word on the form.
Tusko keeps the Rx, the scans and every message on one case that the practice and the lab both open, so a question about a tooth is asked beside the scan.
See how it looks for practices and for labs. For other Canadian rules that touch a lab case, start with CDCP and lab fees.
Is tooth 11 the same tooth in FDI and Universal numbering?
No. In FDI notation, tooth 11 is the upper right central incisor. In the Universal system used in the United States, 11 is the upper left canine. That is why an Rx should say which system it uses.
How do you say an FDI tooth number out loud?
Say the digits one at a time. Tooth 36 is “three six”, because the first digit is the quadrant and the second is the position.
How are baby teeth numbered in FDI notation?
Primary teeth use quadrants 5 to 8 in place of 1 to 4, and positions 1 to 5. Tooth 51 is the upper right primary central incisor.
Which numbering system do Canadian dental labs expect?
FDI notation is the one in common use in Canada. If you send work to a lab in the United States, or your scanner software was set up there, confirm which system it shows.
Sources
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