Tooth surfaces
A tooth surface code says which face of a tooth is being described. Seven letters cover them all, and charting entries combine them — MOD is three of these letters, not a word.
Every tooth has a mesial surface facing the midline, a distal surface facing away from it, a lingual surface facing the tongue, an outer surface, and a biting surface. The last two are named differently front to back: posterior teeth have a buccal face and an occlusal table, anterior teeth have a facial surface and an incisal edge.
The seven surface codes
| Code | Surface | Standard definition | Applies to |
|---|---|---|---|
| M | Mesial | The surface of a tooth which faces toward an invisible line drawn vertically through the centre of the face. | All teeth |
| D | Distal | The surface of the tooth facing away from an invisible line drawn vertically through the centre of the face. | All teeth |
| O | Occlusal | The surfaces of the posterior (back) teeth which provide the chewing function. | Posterior only |
| I | Incisal | The cutting edges of the anterior teeth. | Anterior only |
| B | Buccal | The surface of the tooth which is closest to the cheek. | Posterior only |
| F | Facial | The surface of a tooth that is directed towards the face. | All teeth |
| L | Lingual | The surface of the tooth that is directed towards the tongue. | All teeth |
Definitions are quoted from the tooth surface code list published by the US Centers for Medicare & Medicaid Services through ResDAC. Combination strings such as MOD are a reporting convention built from these seven codes; they are not themselves separately defined codes.
Which surfaces a tooth actually has
The surface set is not the same for every tooth. This is the most common source of notation errors: an O on an incisor or an I on a molar describes a surface that does not exist.
Posterior — premolars and molars
- M Mesial
- D Distal
- B Buccal — the cheek side
- L Lingual — the tongue side, palatal on upper teeth
- O Occlusal — the chewing table
No incisal edge. Universal 1–5, 12–21, 28–32.
Anterior — incisors and canines
- M Mesial
- D Distal
- F Facial — the lip side, also called labial
- L Lingual — the tongue side, palatal on upper teeth
- I Incisal — the biting edge
No occlusal table. Universal 6–11 and 22–27.
Reading combinations
Codes are written together when more than one surface is involved. The order follows the anatomy rather than the alphabet, which is why both MO and DO exist.
| Written | Surfaces | Reads as |
|---|---|---|
| MO | Mesial + Occlusal | Mesio-occlusal |
| DO | Distal + Occlusal | Disto-occlusal |
| MOD | Mesial + Occlusal + Distal | Mesio-occluso-distal |
| MI | Mesial + Incisal | Mesio-incisal, anterior teeth |
| DI | Distal + Incisal | Disto-incisal, anterior teeth |
| MODB | Mesial + Occlusal + Distal + Buccal | Four surfaces of a posterior tooth |
There is no single authority fixing the letter order for every combination, so spellings vary a little between practices and software. The decoder accepts any order and reports the surfaces themselves. More on MOD specifically.
Common questions
- What are the five surfaces of a tooth?
- Every tooth has a mesial surface, a distal surface, a tongue-side lingual surface, an outer surface facing the cheek or lip, and a fifth surface used for biting. On premolars and molars that fifth surface is the occlusal table and the outer surface is called buccal. On incisors and canines it is the incisal edge and the outer surface is called facial or labial.
- What is the difference between mesial and distal?
- Mesial faces toward the midline of the face — the imaginary vertical line between the two central incisors. Distal faces away from it, toward the back of the mouth. Which physical side that is depends on which quadrant the tooth is in.
- What is the difference between buccal and lingual?
- Buccal faces the cheek; lingual faces the tongue. They are opposite surfaces of the same tooth. On upper teeth the lingual surface is often called palatal because it faces the palate.
- Do all teeth have an occlusal surface?
- No. Only posterior teeth — premolars and molars — have an occlusal surface. Incisors and canines have an incisal edge instead, coded I. Writing O on an incisor is a notation error.