Ask candidates what tripped them up on the NDHCE and one answer comes up again and again: tooth numbering. Not because it’s hard — because most widely-available study material is American, and the US uses a completely different system from the one Canada tests. Read a question about “tooth 30” with a Canadian brain, or “tooth 46” with an American one, and you’ll answer confidently and wrongly.
Here’s how to read the Canadian system fluently so it never costs you a mark.
Canada uses FDI (the two-digit system)
The NDHCE uses FDI World Dental Federation notation — also standardized internationally as ISO 3950. Every tooth gets a two-digit number, and each digit means something specific.
First digit = the quadrant. Imagine the mouth split into four quadrants, viewed as if you’re facing the patient:
| First digit | Quadrant (permanent teeth) |
|---|---|
| 1 | Upper right |
| 2 | Upper left |
| 3 | Lower left |
| 4 | Lower right |
For primary (baby) teeth, the same clockwise logic continues with digits 5 (upper right), 6 (upper left), 7 (lower left), 8 (lower right).
Second digit = the tooth’s position from the midline, counting outward:
| Second digit | Tooth |
|---|---|
| 1 | Central incisor |
| 2 | Lateral incisor |
| 3 | Canine |
| 4 | First premolar |
| 5 | Second premolar |
| 6 | First molar |
| 7 | Second molar |
| 8 | Third molar (wisdom tooth) |
So the permanent teeth run 11–18 (upper right), 21–28 (upper left), 31–38 (lower left) and 41–48 (lower right). Primary teeth run 51–55, 61–65, 71–75 and 81–85.
Read it digit by digit. Tooth “46” is spoken “four-six” — quadrant 4 (lower right), tooth 6 (first molar). It is not “forty-six.” Getting comfortable with this rhythm is half the battle.
The US Universal system (what most study material uses)
The American Universal Numbering System ignores quadrants and just counts the permanent teeth 1 through 32 in one continuous sweep:
- Start at the upper right third molar = 1
- Move across the upper arch to the upper left third molar = 16
- Drop down to the lower left third molar = 17
- Sweep across to the lower right third molar = 32
Primary teeth use letters A through T. This is the system baked into most NBDHE question banks, US textbooks and flashcards — which is why borrowed material can quietly mislead you.
Quick conversion for the teeth that matter most
You don’t need to memorize all 32 conversions, but the molars and central incisors come up constantly:
| Tooth | FDI (Canada) | Universal (US) |
|---|---|---|
| Upper right central incisor | 11 | 8 |
| Upper left central incisor | 21 | 9 |
| Upper right first molar | 16 | 3 |
| Upper left first molar | 26 | 14 |
| Lower left first molar | 36 | 19 |
| Lower right first molar | 46 | 30 |
| Lower right third molar | 48 | 32 |
| Upper right third molar | 18 | 1 |
Notice how a single tooth — the lower right first molar — is 46 in Canada but 30 in the US. That one difference has ended more than one otherwise-strong exam performance.
How to make FDI automatic
- Drill the quadrant map first. Once “1 = upper right, clockwise” is reflex, the first digit is free.
- Practise with Canadian resources. The FDHRC’s official preparatory tests use FDI, as does any Canada-specific question bank. If you use US material, mentally convert every tooth as you read it.
- Say it out loud, digit by digit. “Three-six,” not “thirty-six.” This small habit prevents the classic slip.
- Watch case-based questions especially. Perio and radiography cases lean heavily on tooth identification — see the format and blueprint for where these appear.
Tooth numbering is the easiest “hard” topic on the exam: pure convention, zero clinical judgment, fully learnable in an afternoon. Lock in FDI early and you remove one of the most common — and most avoidable — sources of lost marks. For the bigger picture on borrowing US material safely, see NDHCE vs NBDHE, and build it into a full plan with how to prepare for the NDHCE.
Sources: FDI World Dental Federation two-digit notation (ISO 3950); American Dental Association Universal Numbering System. General dental-anatomy references; verify exam specifics at fdhrc.ca.