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# Impression materials: alginate, silicones and polyether

- Dental material

An impression is a mould of the teeth and gums. Alginate is quick and cheap for study models; silicones and polyether are accurate enough for crowns.

Updated Nov 12, 2026

**See it in 3D:** [Maxillae](https://durgical.com/en/anatomy/maxilla/) · [Mandible](https://durgical.com/en/anatomy/mandible/)

## Key points

- Alginate: study models, pour soon.
- Addition silicone: most stable, for crowns; latex can block it.
- Disinfect every impression.

## What it is

An impression records the teeth and surrounding tissues as a negative mould that is poured in gypsum to make a model. Materials are chosen by the accuracy needed. Elastic materials can be pulled past undercuts and spring back; rigid ones cannot. Intraoral scanners now replace many impressions with a digital model.

## Composition and properties

- Alginate (irreversible hydrocolloid): cheap and quick, for study models, opposing models and preliminary denture impressions; it shrinks or swells as it loses or takes up water, so it is poured soon.
- Addition silicone (polyvinyl siloxane): the most dimensionally stable; can be poured later and more than once; used for crowns and bridges.
- Its setting can be blocked by sulphur compounds from some latex gloves.
- Polyether: accurate and naturally wettable, but stiff and harder to remove from undercuts.
- Rigid materials (impression compound, zinc oxide–eugenol paste, plaster) are used mainly for edentulous mouths.

## Uses, limits and safety

- A distorted impression gives a crown that does not fit, however good the laboratory.
- Tray choice, retraction of the gum around the margin and a dry field matter as much as the material.
- Every impression is contaminated with saliva and blood and must be rinsed and disinfected before it goes to the laboratory.

## Next step / Initial management

- Rinse and disinfect each impression with a disinfectant compatible with the material before sending it.
- Pour alginate soon after it is taken; record which material was used for the laboratory.
- Crown or denture that does not fit or rocks: refer back to the dentist; a new impression or scan is often needed.

## Test yourself

Think of the answer, then tap the question to see it.

## Why must an alginate impression be poured soon after it is taken?

It loses or takes up water and changes shape, so the model becomes inaccurate.

## Which impression material is the most dimensionally stable?

Addition silicone (polyvinyl siloxane).

## What can stop addition silicone from setting?

Sulphur compounds from some latex gloves.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/dentistry/impression-materials-alginate-silicones-and-polyether/)

## Connections

## See it in 3D 2

The structures of Durgical's 3D anatomy where it is found.

- [Maxillae](https://durgical.com/en/anatomy/maxilla/)
- [Mandible](https://durgical.com/en/anatomy/mandible/)

## Related 1

- [Gypsum, waxes and dental alloys](https://durgical.com/en/dentistry/gypsum-waxes-and-dental-alloys/)

[← All of dentistry](https://durgical.com/en/dentistry/)

Educational content; it does not replace assessment by a dentist or doctor and is not a clinical instruction. For facial or neck swelling with difficulty swallowing or breathing, a knocked-out tooth or bleeding that will not stop, go to an emergency department at once.

Sources: [Dental Impression Materials](https://www.ncbi.nlm.nih.gov/books/NBK574496/) (StatPearls Publishing (NCBI Bookshelf), 2023); [Dental Alginate Impressions](https://www.ncbi.nlm.nih.gov/books/NBK470480/) (StatPearls Publishing (NCBI Bookshelf), 2023).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/dentistry/impression-materials-alginate-silicones-and-polyether/