Tooth Numbering: FDI, Universal and Palmer Systems

The FDI World Dental Federation system was introduced in 1970 and is now the most widely adopted system globally. Its logic is straightforward: each tooth is described by two digits. The first digit names the quadrant; the second names the tooth's position within that quadrant counting from the midline outward.

1. Quadrant codes (first digit)
   Permanent dentition: 1 = upper right, 2 = upper left, 3 = lower left, 4 = lower right. Deciduous dentition: 5 = upper right, 6 = upper left, 7 = lower left, 8 = lower right. The numbering proceeds clockwise when the dentition is viewed from the front.
2. Position codes (second digit)
   1 = central incisor, 2 = lateral incisor, 3 = canine, 4 = first premolar, 5 = second premolar, 6 = first molar, 7 = second molar, 8 = third molar. For deciduous teeth the second digit runs 1-5 (1 = central incisor, 2 = lateral incisor, 3 = canine, 4 = first molar, 5 = second molar).
3. Reading the code
   FDI 36 is lower left first molar. FDI 21 is upper left central incisor. FDI 54 is the upper right first deciduous molar. Spoken aloud, FDI codes are read as two separate digits: 'three-six', not 'thirty-six', to avoid confusion with the Universal system.

The Universal system numbers all 32 permanent teeth in a single uninterrupted sequence that begins at the maxillary right third molar and runs clockwise around the arches back to the mandibular right third molar. The starting point is arbitrary, chosen when the system was adopted by the American Dental Association in 1975, but the sequence is now fixed in North American clinical records and in the software systems used by most US dental practices.

Starting at the maxillary right third molar (tooth 1) the sequence crosses the upper arch from right to left: 1 through 16 covers the entire maxillary arch, ending at the maxillary left third molar. The count then drops to the mandibular arch and continues from left to right: 17 (mandibular left third molar) through 32 (mandibular right third molar). Deciduous teeth use the letters A through T in the same clockwise order, starting at the maxillary right second molar (A) and ending at the mandibular right second molar (T).

Palmer notation, developed by American dentist Corydon Palmer in 1870 and refined by the dental anatomist Zsigmondy, uses a graphical quadrant symbol rather than a numeric code. A horizontal line separates the upper arch from the lower. A vertical line separates the left half from the right. Together they form a cross, and each of the four right-angle bracket symbols that result from this cross marks a different quadrant.

Within each quadrant the tooth is identified by a number from 1 to 8 for permanent teeth (1 = central incisor, 8 = third molar, counting from midline outward) or a letter A to E for deciduous teeth (A = central incisor, E = second molar). The bracket tells you which quadrant; the number tells you which tooth. To write Palmer notation in plain text, the quadrant is indicated by placing the number inside or adjacent to the appropriate bracket character. In print and in electronic records Palmer is often rendered with a superscript or subscript depending on arch, which creates ambiguity when text is copied into a different system.

The safest approach at the start of any cross-border comparison is to write out the full conversion for the key teeth before comparing records. The table below covers the complete permanent maxillary right quadrant as an example. The full 32-tooth conversion follows the same logic.

Notice that the FDI second digit always runs from 1 at the midline to 8 at the back. Universal numbers run in the opposite direction in the upper arch (decreasing toward the midline on the left, increasing on the right). Palmer's position number matches the FDI second digit in every case, which makes Palmer-to-FDI conversion the most mechanical: replace the bracket symbol with the appropriate FDI first digit, keep the position number as the FDI second digit.

The deciduous dentition has its own notation in each system. In FDI, deciduous quadrants are coded 5 through 8 (5 = upper right, 6 = upper left, 7 = lower left, 8 = lower right) with position digits 1 through 5. So FDI 64 is the upper left first deciduous molar. In Universal, deciduous teeth are lettered A through T in the same clockwise order as the permanent numbers, starting at the upper right second deciduous molar (A) and ending at the lower right second deciduous molar (T). In Palmer, letters A through E replace the numbers 1 through 5.

In routine clinical dentistry a notation error causes, at worst, a misunderstanding at the next appointment. In forensic identification it can delay a match, mislead an investigation, or cause an identification to be rejected. The reason is that comparison software and human examiners both treat a tooth number as ground truth. If the ante-mortem record says tooth 30 has a mesial amalgam restoration and the postmortem chart records tooth 46 with the same restoration, the match depends entirely on the examiner knowing that 30 and 46 are the same tooth.

The INTERPOL DVI Standing Committee requires that all dental data entered on DVI forms use FDI notation. This is not a preference. It is a procedural requirement that exists precisely because of the historical record of notation-conversion errors causing delays in mass-casualty identification. When an odontologist receives ante-mortem records from a North American source, the conversion to FDI is the first step of the comparison, done before any tooth-by-tooth comparison begins, and it is documented in the case file.

The practical skill required is not complicated. A conversion table and 10 minutes of systematic work translates any record into the working notation. The skill is recognising that the conversion is necessary, which means knowing that other systems exist and differ, which is exactly what this topic provides.