Tooth Numbering: the FDI System Compared with Universal and Palmer

In short: The FDI system (ISO 3950) numbers each tooth with two digits: the quadrant (1 to 4 permanent, 5 to 8 primary), then the tooth's position from the central incisor to the wisdom tooth. So 16 is the upper right first molar, read "one six". Right and left are the patient's, not the dentist's.

Prepared by the Synora team, based on the ISO 3950:2016 standard. Last updated: 30 September 2026.

What is the FDI system and why is it used?

FDI is a tooth designation system that gives each tooth just two digits. The archived page of the FDI World Dental Federation describes it as a system the Federation created in 1971, also known as “ISO 3950 notation”. The ISO 3950 standard published in 2016 (the fourth edition, which ISO reviewed and confirmed in 2022) describes a two-digit system for designating teeth or areas of the oral cavity.

Its practical value is that anyone who reads the file, whether a dentist, an assistant, a lab or a colleague receiving a referral, understands which tooth is meant without explanation. We do not reproduce the text of the standard here, as ISO sells it; we explain the rule and point you to the source.

How do I read a tooth number in the FDI system?

The number has two digits: the first digit is the quadrant, and the second digit is the tooth’s position within the quadrant, starting from the central incisor at the midline (number 1) and ending with the wisdom tooth (number 8).

The right and left rule: they are the patient’s right and left, not those of the dentist facing them, as in the rest of medicine. The quadrants are numbered clockwise, starting from the patient’s upper right quadrant.

Quadrant	Location	Permanent teeth	Primary teeth
1	Upper right	11 to 18	51 to 55
2	Upper left	21 to 28	61 to 65
3	Lower left	31 to 38	71 to 75
4	Lower right	41 to 48	81 to 85

Position number	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 (wisdom tooth)

Example: 26 is quadrant 2 (upper left) and position 6, so the upper left first molar. And 48 is the lower right wisdom tooth.

How are primary teeth numbered?

There are twenty primary teeth, and they use quadrants 5 to 8 in the same direction: 5 upper right, 6 upper left, 7 lower left, 8 lower right. Each quadrant has five teeth numbered 1 to 5: two incisors, a canine, then two primary molars. So 75 is the lower left second primary molar, and 51 is the upper right primary central incisor.

In the mixed dentition stage both kinds are in the same mouth, so you will find numbers from 1 to 4 and others from 5 to 8 in the same file, and that is normal.

What is the Universal system?

The Universal system numbers permanent teeth in sequence from 1 to 32, and primary teeth with the letters A to T. Counting starts at the upper right wisdom tooth (number 1) and moves across the upper arch to the upper left wisdom tooth (16), then goes down to the lower left wisdom tooth (17) and continues to the lower right wisdom tooth (32). This system is widely used in the United States.

Its practical drawback is that the number alone does not reveal the quadrant or the type of tooth, so you have to memorise the sequence or check the table.

What is the Palmer system?

The Palmer system uses a symbol for the quadrant together with the position number from 1 to 8 for permanent teeth, and a letter from A to E for primary teeth. The symbol is usually drawn as an angle around the number: ┘ for upper right, └ for upper left, ┐ for lower left, and ┌ for lower right. Writing it needs special symbols, so the symbol is easily lost when copied into email or messages, leaving a number with no quadrant. In the table below we use a simplified text form of it.

What is the conversion table between FDI, Universal and Palmer?

Permanent teeth (32 teeth):

FDI	Universal	Palmer	Tooth
11	8	┘1	Upper right central incisor
12	7	┘2	Upper right lateral incisor
13	6	┘3	Upper right canine
14	5	┘4	Upper right first premolar
15	4	┘5	Upper right second premolar
16	3	┘6	Upper right first molar
17	2	┘7	Upper right second molar
18	1	┘8	Upper right third molar
21	9	└1	Upper left central incisor
22	10	└2	Upper left lateral incisor
23	11	└3	Upper left canine
24	12	└4	Upper left first premolar
25	13	└5	Upper left second premolar
26	14	└6	Upper left first molar
27	15	└7	Upper left second molar
28	16	└8	Upper left third molar
31	24	┐1	Lower left central incisor
32	23	┐2	Lower left lateral incisor
33	22	┐3	Lower left canine
34	21	┐4	Lower left first premolar
35	20	┐5	Lower left second premolar
36	19	┐6	Lower left first molar
37	18	┐7	Lower left second molar
38	17	┐8	Lower left third molar
41	25	┌1	Lower right central incisor
42	26	┌2	Lower right lateral incisor
43	27	┌3	Lower right canine
44	28	┌4	Lower right first premolar
45	29	┌5	Lower right second premolar
46	30	┌6	Lower right first molar
47	31	┌7	Lower right second molar
48	32	┌8	Lower right third molar

Primary teeth (20 teeth):

FDI	Universal	Palmer	Tooth
51	E	┘A	Upper right primary central incisor
52	D	┘B	Upper right primary lateral incisor
53	C	┘C	Upper right primary canine
54	B	┘D	Upper right first primary molar
55	A	┘E	Upper right second primary molar
61	F	└A	Upper left primary central incisor
62	G	└B	Upper left primary lateral incisor
63	H	└C	Upper left primary canine
64	I	└D	Upper left first primary molar
65	J	└E	Upper left second primary molar
71	O	┐A	Lower left primary central incisor
72	N	┐B	Lower left primary lateral incisor
73	M	┐C	Lower left primary canine
74	L	┐D	Lower left first primary molar
75	K	┐E	Lower left second primary molar
81	P	┌A	Lower right primary central incisor
82	Q	┌B	Lower right primary lateral incisor
83	R	┌C	Lower right primary canine
84	S	┌D	Lower right first primary molar
85	T	┌E	Lower right second primary molar

What are the names of the tooth surfaces?

When recording caries or a filling, the tooth number is not enough: you also need the surface. Surfaces are named relative to the direction of the dental arch:

Surface	Meaning
Mesial	The side closest to the midline of the face
Distal	The side farthest from the midline
Occlusal	The chewing surface of premolars and molars
Incisal	The edge of incisors and canines
Buccal	The side facing the cheek (called Labial on front teeth)
Lingual	The side facing the tongue (called Palatal in the upper jaw)

How does Synora’s dental chart use the FDI system?

We checked the following in the software’s code and screens:

• Numbers: the 2D dental chart shows the FDI number above each tooth, and the teeth field in lab cases accepts FDI numbers only, from 11 to 48 and from 51 to 85.
• Permanent, primary and mixed teeth: each patient has a permanent, primary or mixed display mode.
• Surfaces: when recording a tooth’s condition you choose: the whole tooth, occlusal, mesial, distal, buccal, lingual or incisal. Front teeth (incisors and canines) get “incisal” instead of “occlusal”, and back teeth (premolars and molars) get “occlusal”. The software does not separate “buccal” from “labial”, or “lingual” from “palatal”.
• Current limits: the screens do not show Universal or Palmer numbering, so use the conversion table above when dealing with someone who uses them.

To learn more about charting and treatment plans, see Synora’s dental chart. The free plan includes the dental chart (up to 50 patients and one account), and the software runs in the browser with nothing to download; details are in Free dental software and the getting started guide.

Note: This content is for general awareness and guidance only and is not legal, tax or medical advice. Check with the Dental Syndicate, the Ministry of Health and your accountant.

Sources

1. ISO 3950:2016, Dentistry: Designation system for teeth and areas of the oral cavity (standard page at ISO, accessed 30 September 2026)
2. FDI World Dental Federation, "FDI Two-Digit Notation" (archived copy from October 2007, accessed 30 September 2026)
3. FDI World Dental Federation, official website (accessed 30 September 2026)