Feline Odontic Resorptive Lesions (Cavities) in Cats

Last Updated on March 8, 2021 by Julia Wilson

Also known as tooth resorptive lesions or cervical line lesions, feline odontoclastic resorptive lesions (FORL) is a common dental disorder in which odontoclasts (specialist cells responsible for reabsorbing the roots of deciduous or baby teeth) are reactivated and reabsorb the adult roots of the tooth.  FORL occurs in between 20-75% of cats, the cause is unknown.

Lesions fall into three categories:

  • Internal resorptive lesions – Lesions begin in the inner structures of the tooth and don’t become apparent until they work their way to the outside.
  • External ondoclastic resorption – These lesions begin at the cementoenamel junction (neck of the tooth).
  • Cervical line erosions – Occurring along or just above the gum line on the teeth.

Your veterinarian will stage the FORL to determine the amount of destruction to the tooth.

Stage 1 – There is an erosion of the enamel. The root and periodontal ligament are normal. Mild pain may be present.

Stage 2 – Erosion of the enamel and dentin (bony tissue underneath the enamel).

Stage 3 – Dental tissue deep within the tooth is lost (enamel, cementum, dentin extending into the pulp cavity). The tooth is still structurally stable.

Stage 4 – Dental tissue deep inside the tooth is lost and the tooth is no longer structurally stable.

Stage 5 – The tooth is almost entirely resorbed, with gingival tissue covering the area.


  • Pain when eating, or reluctance to eat, especially hard food
  • Drooling
  • Bleeding from the mouth
  • Granulation tissue is a visible hole or gum tissue growing over the tooth

Obviously, internal resorptive lesions may be harder to identify unless the lesion has made its way to the outside. This is why it is important to see your veterinarian if you notice any symptoms such as reluctance to eat or drooling as these can be a sign of an underlying problem.


Your veterinarian will perform a close examination of your cat’s mouth, carefully checking the teeth and gums.

Dental X-rays are necessary as resorption can develop from the inside out and may not be visible.


Treatment will depend on the severity of FORL. 

Stage 1 – Application of fluoride varnish or sealant over the tooth.

Crown amputation – Remove the tooth to the level of the gum, leaving the root fragments intact, gum tissue covers the underlying area.

Moderate to Severe FORL – Surgical removal of the entire tooth, which will be performed under general anesthesia.

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