Tooth number 21 is the lower left first premolar, a permanent (adult) tooth. In the FDI (ISO 3950) system it is 34, and in Palmer notation it is ┌4.
Tooth #21 at a glance
| Universal (US) | 21 |
| FDI / ISO 3950 | 34 |
| Palmer | ┌4 |
| Name | Lower left first premolar |
| Type | First premolar (adult tooth) |
| Jaw | Lower (mandible) |
| Side | Patient’s left |
| Comes in | 10-12 yrs |
| Roots | 1 |
| Root canals (usual) | 1 |
| Chewing surface | 2 cusps (one large, one small) |
Where it is and what it does
It sits in the lower jaw on the patient’s left side, fourth from the midline, just behind the canine. Premolars (also called bicuspids) crush and tear food. They sit between the canines and the molars and share the work of both.
Neighbouring and related teeth
- In front of it (toward the midline): Tooth number 22, the lower left canine
- Behind it: Tooth number 20, the lower left second premolar
- Same tooth on the other side: Tooth number 28
- The matching tooth in the upper jaw: Tooth number 12
- Replaces: Baby tooth L, the baby lower left first molar
Common dental work on this tooth
Premolars commonly get fillings. First premolars are also the teeth most often removed to make space for orthodontic treatment (braces).
Questions
What tooth is number 21?
Tooth number 21 is the lower left first premolar. Numbers 1 to 32 are used for adult teeth in the Universal system used in the United States, starting with the upper right wisdom tooth.
What is tooth number 21 in the FDI and Palmer systems?
In FDI it is 34, said digit by digit (“three-four”). The first digit is the quadrant and the second is the position from the midline. In Palmer notation it is ┌4.
When does tooth 21 come in?
Usually at about 10-12 yrs. Timing varies from person to person.
For education only. This is not dental advice; your dentist can tell you what is right for your own teeth.