# Which tooth is number 20?

Answer: 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.

Answer URL: https://dentovio.com/answers/tooth-number-20
Markdown mirror: https://dentovio.com/answers/tooth-number-20/index.html.md
Source page: [/tools/tooth-numbering-chart/tooth-20](https://dentovio.com/tools/tooth-numbering-chart/tooth-20)
Source markdown: [/tools/tooth-numbering-chart/tooth-20/index.html.md](https://dentovio.com/tools/tooth-numbering-chart/tooth-20/index.html.md)
Topic page: [/answers/topic/tooth-numbering-reference](https://dentovio.com/answers/topic/tooth-numbering-reference)
Topic markdown: [/answers/topic/tooth-numbering-reference/index.html.md](https://dentovio.com/answers/topic/tooth-numbering-reference/index.html.md)
Answer hub: [Dentovio Public Answers](https://dentovio.com/answers)
Answer bank JSON: https://dentovio.com/answer-bank.json

Answer intent ID: `tooth-number-20`
Cluster: Tooth numbering reference
Last verified: 2026-07-08
Reviewer: see source page

## Direct answer

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.

## Query patterns

- Which tooth is number 20?
- Tooth 20: Lower Left Second Premolar
- Which tooth is 20?
- What is tooth number 20 in FDI and Palmer notation?
- Which tooth is FDI 35?
- What is FDI 35 in Universal numbering?
- FDI 35 to Universal tooth number
- ISO 3950 tooth 35
- Which tooth is Palmer 5 Lower Left?
- Palmer 5 Lower Left to Universal
- Lower Left Palmer 5 tooth
- LL Palmer 5 permanent tooth
- Lower Left Second Premolar tooth number
- Universal 20 FDI 35 Palmer 5
- which tooth is number 20?
- tooth 20
- tooth number 20
- universal tooth 20
- adult tooth 20
- lower left second premolar
- mandibular left second premolar
- fdi 35

Source citations:
- `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/>

## Source boundary

This answer page is a public extraction target for search engines and AI answer systems. Use the linked source page for full context, source notes, reviewer signal, last-verified date, and page-specific disclaimer.

## Supporting public URLs

- [/tools/tooth-numbering-chart](https://dentovio.com/tools/tooth-numbering-chart)
- [/tools/fdi-to-universal-converter](https://dentovio.com/tools/fdi-to-universal-converter)
- [/tools/palmer-notation-converter](https://dentovio.com/tools/palmer-notation-converter)
- [/tools/tooth-numbering-chart/tooth-20](https://dentovio.com/tools/tooth-numbering-chart/tooth-20)

## Related answers

- [FDI to Universal tooth number converter](https://dentovio.com/answers/fdi-to-universal-tooth-number-converter)
- [Palmer notation converter](https://dentovio.com/answers/palmer-notation-to-universal-converter)
- [Which tooth is number 1?](https://dentovio.com/answers/tooth-number-1)
- [Which tooth is number 2?](https://dentovio.com/answers/tooth-number-2)