The Universal system is the one used in most U.S. offices and on DANB exams. Permanent teeth are numbered 1 to 32, primary teeth are lettered A to T, and both run the same loop around the mouth.
The loop
Start at the patient's upper right third molar (#1). Count across the upper arch to the upper left third molar (#16). Drop down to the lower left third molar (#17) and count across the lower arch to the lower right third molar (#32). It's one continuous loop: clockwise from the dentist's view, which is the patient's right to left on top, then left to right on the bottom.
Primary teeth work the same way with letters: A is the upper right second primary molar, J is the upper left second primary molar, K is the lower left, and T is the lower right.
Landmarks that keep you oriented
- Upper right central incisor is #8, upper left central is #9. The midline on top sits between 8 and 9.
- Lower left central is #24, lower right central is #25. The midline on the bottom sits between 24 and 25.
- Premolars: 4, 5 (upper right), 12, 13 (upper left), 20, 21 (lower left), 28, 29 (lower right).
- Canines (cuspids): 6, 11, 22, 27.
- First molars, the six-year molars: 3, 14, 19, 30.