Tooth Numbering & Surface Terminology

Three numbering systems side by side

Tooth	Universal (ADA)	FDI (ISO 3950)	Palmer
Maxillary right third molar	1	18	8 in the upper-right bracket
Maxillary right first molar	3	16	6 upper right
Maxillary right central incisor	8	11	1 upper right
Maxillary left central incisor	9	21	1 upper left
Maxillary left third molar	16	28	8 upper left
Mandibular left third molar	17	38	8 lower left
Mandibular left first molar	19	36	6 lower left
Mandibular right canine	27	43	3 lower right
Mandibular right first molar	30	46	6 lower right
Mandibular right third molar	32	48	8 lower right

Universal runs clockwise from the dentist's view: maxillary right to maxillary left (1–16), then mandibular left to mandibular right (17–32).
FDI: first digit is the quadrant (1 UR, 2 UL, 3 LL, 4 LR; primary 5–8), second digit counts from the midline (1 = central incisor, 8 = third molar). Read '11' as 'one-one', not 'eleven'.

Tooth	Universal	FDI
Maxillary right second molar	A	55
Maxillary right central incisor	E	51
Maxillary left central incisor	F	61
Maxillary left second molar	J	65
Mandibular left second molar	K	75
Mandibular right first molar	S	84
Mandibular right second molar	T	85

Primary teeth use letters A–T in the same clockwise order; there are no primary premolars or third molars, so each quadrant has 5 teeth.

Anterior teeth: facial (labial), lingual, mesial, distal and an incisal edge; posterior teeth have an occlusal surface instead.
A line angle joins two surfaces (mesiofacial); a point angle joins three (mesiofacioincisal).
Each anterior tooth has 6 line angles and 4 point angles; each posterior tooth has 8 line angles and 4 point angles. (The incisal 'line angles' are commonly combined, which is why anteriors have fewer.)
Name combined surfaces with the -al ending dropped to -o: mesio-occlusal (MO), mesio-occluso-distal (MOD), disto-lingual (DL).
Crown thirds: viewed from facial or lingual, a crown is divided incisally/occlusally, middle and cervically; viewed proximally, facially, middle and lingually.

Height of contour (crest of curvature): facial surfaces of all teeth and lingual surfaces of anterior teeth sit in the cervical third; lingual surfaces of posterior teeth sit in the middle third.
Proximal contacts move from the incisal third (central incisors) toward the middle third as you go back in the arch, and distal contacts sit more cervically than mesial contacts on most teeth.
Embrasures are the V-shaped spaces around a contact: occlusal/incisal, gingival (filled by the papilla in health), facial and lingual. Incisal embrasures widen from central incisor to canine.

Counting Universal numbers counterclockwise (starting at the mandibular right): #17 is the mandibular LEFT third molar, not the right.
Reading FDI '21' as the 21st tooth. It means quadrant 2 (upper left), tooth 1 (central incisor) = Universal #9.
Giving anterior teeth 8 line angles: they have 6.
Placing the lingual height of contour of a mandibular molar in the cervical third: posterior lingual contours are in the middle third.

Universal: '1 to 16 across the top, right to left as you face the patient; 17 drops straight down to the bottom left.'
FDI quadrants go 1-2-3-4 clockwise from the patient's upper right, like Universal; add 4 for primary (5-6-7-8).

Pick an answer to see right away whether it is correct and why.

What is the Universal number of the mandibular left first molar?
In the FDI system, tooth 46 is:
Primary tooth K is the:
How many line angles does a permanent mandibular first premolar have?
Where is the height of contour on the LINGUAL surface of a maxillary first molar?

0 of 5 answered

Answer key: 1 A · 2 A · 3 B · 4 D · 5 B

Dental School Map · Original study material, written and checked by our team; always confirm clinical decisions against current guidelines.