# Tooth 20: Lower Left Second Premolar

> In the Universal Numbering System, tooth 20 is the lower left second premolar (mandibular left second premolar). Its FDI (ISO 3950) designation is 35 and its Palmer designation is 5 in the lower left quadrant. It is a premolar in the lower arch with typically 1 root.

URL: https://dentovio.com/tools/tooth-numbering-chart/tooth-20

Markdown: https://dentovio.com/tools/tooth-numbering-chart/tooth-20/index.html.md

Last verified: 2026-07-08

Neutral tooth-designation reference only; not clinical, diagnostic, or treatment advice. Root counts describe typical permanent-tooth morphology and vary between individuals.

## Direct answer

- Which tooth is number 20? In the Universal Numbering System, tooth 20 is the lower left second premolar (mandibular left second premolar). Its FDI (ISO 3950) designation is 35 and its Palmer designation is 5 in the lower left quadrant. It is a premolar in the lower arch with typically 1 root.
- Universal number: 20
- FDI / ISO 3950 designation: 35
- Palmer designation: 5 LL
- Plain-language name: Lower Left Second Premolar
- Anatomical name: Mandibular Left Second Premolar
- Quadrant: Lower Left
- Arch and side: lower, left
- Type: premolar
- Typical roots: 1

## Conversion table

| System | Designation |
| --- | --- |
| Universal Numbering System | 20 |
| FDI / ISO 3950 | 35 |
| Palmer notation | 5 LL |
| Tooth name | Lower Left Second Premolar |

## Search terms

- which tooth is number 20?
- tooth 20
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- universal tooth 20
- adult tooth 20
- lower left second premolar
- mandibular left second premolar
- fdi 35
- palmer 5
- lower left tooth 5
- lower left premolar

## Sources

- `TOOTH-1` American Dental Association — Universal Numbering System. <https://www.ada.org/publications/ada-news/2020/november/how-to-count-teeth-numbering-systems>
- `TOOTH-2` ISO 3950:2016 — Dentistry, designation system for teeth and areas of the oral cavity (FDI two-digit). <https://www.iso.org/standard/68292.html>
- `TOOTH-3` FDI World Dental Federation — two-digit notation. <https://www.fdiworlddental.org/>

## Related

- [Full tooth numbering chart](https://dentovio.com/tools/tooth-numbering-chart/index.html.md)
- [FDI to Universal converter](https://dentovio.com/tools/fdi-to-universal-converter/index.html.md)
- [Palmer notation converter](https://dentovio.com/tools/palmer-notation-converter/index.html.md)
- [Previous tooth: Tooth 19: Lower Left First Molar](https://dentovio.com/tools/tooth-numbering-chart/tooth-19/index.html.md)
- [Next tooth: Tooth 21: Lower Left First Premolar](https://dentovio.com/tools/tooth-numbering-chart/tooth-21/index.html.md)