Tooth groups and anatomical formulas
Normally, humans have two types of occlusion/dentition: temporary and permanent. They differ in the number of elements and group affiliation.
Temporary teeth (dentes decidui) include 20 elements. Each half of the jaw contains two incisors, one canine, and two molars. An important feature is that children completely lack premolars and third molars. The anatomical formula is written as I 2 — C 1 — M 2.
Permanent dentition consists of 28–32 teeth (third molars do not erupt in everyone). Here, one quarter of the jaw accounts for eight teeth: two incisors, one canine, two premolars, and three molars. The group anatomical formula is 2.1.2.3 (or I 2 — C 1 — P 2 — M 3).
Clinical formula (Zsigmondy–Palmer system)
In this system, dental arches are divided into four quadrants using horizontal and median (vertical) planes. Numbering is always conducted from the central line (from the incisors) to the periphery (to the molars).
- For permanent teeth, Arabic numerals from 1 to 8 are used.
- For primary teeth, Roman numerals from I to V are used.
To indicate a specific tooth in an isolated record, a special "bracket" is used, which graphically shows the quadrant. For example, the symbol 6| (angle at bottom right) denotes the upper right first molar, and |7 (angle at top left) denotes the lower left second molar. The order of recording in the chart always corresponds to how the physician sees the patient sitting opposite them.
FDI International System (WHO)
The two-digit FDI system, proposed in 1971, is the international standard. It is most convenient for maintaining medical records and describing radiographs. Each tooth is coded with two Arabic numerals:
- The first digit indicates the quadrant. For permanent dentition, these are 1 (upper right jaw — dextra), 2 (upper left jaw — sinistra), 3 (lower left jaw), and 4 (lower right jaw). For primary dentition, digits from 5 to 8 are used respectively.
- The second digit indicates the position of the tooth in the quadrant (from 1 to 8 for permanent, from 1 to 5 for primary).
Reading rule: the digits are pronounced strictly separately. The record 4.4 is read as "four-four" (lower right first premolar), and 2.1 as "two-one" (upper left central incisor).
Universal (American) system
Adopted in 1975, but not widely used in the Russian Federation. Its essence is continuous numbering of all permanent teeth from 1 to 32.
Counting starts from the upper right third molar (tooth #1), proceeds along the upper jaw to the left, descends to the lower jaw, and returns to the lower right third molar (tooth #32). For example, the sixth upper right tooth is designated by the digit 3, and the lower right sixth by the digit 30.
Chronology of permanent tooth eruption
The process of replacing temporary teeth with permanent ones starts at the age of 5–6 years. The first to appear in the permanent dentition are not the incisors, but the first molars.
Further sequence of eruption:
- Central incisors: 6–8 years;
- Lateral incisors: 8–9 years;
- First premolars: 9–10 years;
- Canines: 10–11 years;
- Second premolars: 11–12 years;
- Second molars: 12–13 years;
- Third molars: 20–25 years.
To easily remember the order of quadrants in the FDI and Universal systems, use the "clock hand" rule. Counting always starts from the patient's upper right jaw (to the doctor, this is on the left) and goes in a circle: upper-right, upper-left, lower-left, lower-right.
Class and exam questions
How to distinguish primary from permanent dentition in a dental formula?
There are only 20 teeth in the primary dentition, with a complete absence of premolars and third molars. Clinically they are designated by Roman numerals (I–V), and in the international FDI system by quadrants 5 to 8.
Which tooth erupts first during dental transition?
The first permanent tooth to appear is the first molar. This process begins at the age of 5–6 years.
How to correctly pronounce tooth numbers according to the WHO (FDI) system?
The two digits are always named separately. For example, tooth 26 is pronounced as "two-six" (upper left first molar), rather than "twenty-six".
What else to study on this topic
- Graphical display of quadrants in the Zsigmondy–Palmer system
- Features of dental formula recording in radiological reports
- Morphological differences between primary and permanent teeth
- Anomalies in tooth eruption timing
- Detailed analysis of the Universal American numbering system
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