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# Internal and external root resorption

- Oral pathology

Resorption is the tooth being eaten away by the body's own cells, from inside the canal or from the root surface. It is often silent and found on a radiograph.

Updated Nov 12, 2026

## Key points

- Internal: balloon in the canal; root canal treatment.
- External inflammatory: necrotic pulp after trauma; root canal treatment.
- Ankylosis: metallic percussion, sinking tooth.

## What it is

Root resorption happens when clast cells reach the root, usually after the protective layer of cementum or predentine is damaged and something keeps them active: infection, pressure or inflammation. Internal resorption starts in an inflamed pulp; external resorption starts on the root surface and has several types with different causes and treatments. Most cases have no symptoms until late.

## How to recognise it

- Internal: a round, balloon-like widening of the canal outline on the radiograph; driven by inflamed pulp; treated with root canal treatment.
- External inflammatory: after trauma with a necrotic infected pulp; stopped by root canal treatment.
- Replacement resorption (ankylosis): bone replaces the root after severe damage to the ligament, often after avulsion; a high, metallic percussion sound and, in children, a tooth that sinks below its neighbours.
- External cervical (invasive) resorption: starts near the gum line; linked to trauma, orthodontics and internal bleaching; may show a pink spot.
- Pressure resorption: from an impacted canine, a tumour or orthodontic force.

## Differential and risks

- Changing the radiograph angle helps: an internal lesion stays with the canal; an external one moves.
- CBCT shows the size and position of resorption and whether it can be repaired.
- Replacement resorption in a growing child can leave a sunken tooth and a bone defect; timing of removal matters.

## Next step / Initial management

- Look for resorption on radiographs after dental trauma and during orthodontic treatment.
- Any resorption found: refer to the dentist or endodontist; the type decides between root canal treatment, repair, monitoring or extraction.
- Avulsed and replanted teeth: follow up with radiographs for at least several years.

## Test yourself

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

## How does internal resorption look on a radiograph?

A round, balloon-like widening continuous with the canal outline.

## Which type of resorption follows severe ligament damage after avulsion?

Replacement resorption (ankylosis), in which bone replaces the root.

## What is one risk factor for external cervical resorption?

Any of: dental trauma, orthodontic treatment, internal bleaching.

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## Connections

## Related 3

- [Knocked-out tooth: replant within minutes](https://durgical.com/en/dentistry/knocked-out-tooth-replant-within-minutes/)
- [Tooth discoloration and whitening](https://durgical.com/en/dentistry/tooth-discoloration-and-whitening/)
- [Dental imaging: bitewing, periapical, panoramic and CBCT](https://durgical.com/en/dentistry/dental-imaging-bitewing-periapical-panoramic-and-cbct/)

[← 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: [Tooth root resorption: A review](https://pmc.ncbi.nlm.nih.gov/articles/PMC10358711/) (Science Progress (PMC open access), 2022); [Tooth Resorption, Part 1: The evolvement, rationales and controversies of tooth resorption](https://pmc.ncbi.nlm.nih.gov/articles/PMC9546147/) (Dental Traumatology (PMC open access), 2022); [External cervical resorption: Radiological diagnosis and literature (Review)](https://pmc.ncbi.nlm.nih.gov/articles/PMC8353645/) (Experimental and Therapeutic Medicine (PMC open access), 2021).

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Representative model, for educational purposes only.

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