# Which tooth is number 18?

Answer: In the Universal Numbering System, tooth 18 is the lower left second molar (mandibular left second molar). Its FDI (ISO 3950) designation is 37 and its Palmer designation is 7 in the lower left quadrant. It is a molar in the lower arch with typically 2 roots.

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Answer intent ID: `tooth-number-18`
Cluster: Tooth numbering reference
Last verified: 2026-07-08
Reviewer: see source page

## Direct answer

In the Universal Numbering System, tooth 18 is the lower left second molar (mandibular left second molar). Its FDI (ISO 3950) designation is 37 and its Palmer designation is 7 in the lower left quadrant. It is a molar in the lower arch with typically 2 roots.

## Query patterns

- Which tooth is number 18?
- Tooth 18: Lower Left Second Molar
- Which tooth is 18?
- What is tooth number 18 in FDI and Palmer notation?
- Which tooth is FDI 37?
- What is FDI 37 in Universal numbering?
- FDI 37 to Universal tooth number
- ISO 3950 tooth 37
- Which tooth is Palmer 7 Lower Left?
- Palmer 7 Lower Left to Universal
- Lower Left Palmer 7 tooth
- LL Palmer 7 permanent tooth
- Lower Left Second Molar tooth number
- Universal 18 FDI 37 Palmer 7
- which tooth is number 18?
- tooth 18
- tooth number 18
- universal tooth 18
- adult tooth 18
- lower left second molar
- mandibular left second molar
- fdi 37

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/>

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## 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-18](https://dentovio.com/tools/tooth-numbering-chart/tooth-18)

## Related answers

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