# Tooth 18: Lower Left Second Molar

> 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.

URL: https://dentovio.com/tools/tooth-numbering-chart/tooth-18

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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 18? 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.
- Universal number: 18
- FDI / ISO 3950 designation: 37
- Palmer designation: 7 LL
- Plain-language name: Lower Left Second Molar
- Anatomical name: Mandibular Left Second Molar
- Quadrant: Lower Left
- Arch and side: lower, left
- Type: molar
- Typical roots: 2

## Conversion table

| System | Designation |
| --- | --- |
| Universal Numbering System | 18 |
| FDI / ISO 3950 | 37 |
| Palmer notation | 7 LL |
| Tooth name | Lower Left Second Molar |

## Search terms

- which tooth is number 18?
- tooth 18
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- lower left second molar
- mandibular left second molar
- fdi 37
- palmer 7
- lower left tooth 7
- lower left molar

## 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 17: Lower Left Third Molar](https://dentovio.com/tools/tooth-numbering-chart/tooth-17/index.html.md)
- [Next tooth: Tooth 19: Lower Left First Molar](https://dentovio.com/tools/tooth-numbering-chart/tooth-19/index.html.md)