Feline odontoclastic resorptive lesions (FORLs) have been known by many names over the years. These include neck lesions, cervical lesions, cervical line lesions, feline caries, dental resorptive lesions, external odontoclastic resorptions, cervical root resorptions, feline odontolysis and most likely many more.


This variation in name creates difficulties for literature reviews, as location of valuable references may not be found. A recently “discovered” journal article indicates that the disease entity was known to exist in the 1920’s. A.M. Reiter reviewed this article by Prof. Arthur Hopewell-Smith recently in the Journal of Veterinary Dentistry.


Not only did Hopewell-Smith know of the lesions in cats, he described the stages of the disease histopathologically (with photomicrographs to prove his theories).

What are FORLs?

Basically, the name explains the condition well. Odontoclasts are cells whose normal function in life is to remove the roots of the deciduous teeth as the permanents erupt. Once the permanent dentition is fully erupted, odontoclasts have no further normal function.



For some reason, in some cats, the stem cells in the periodontal ligament differentiate into odontoclasts (no one has yet ascertained what the stimulus is) and these begin to attack the dental structures. These are not carious lesions. Odontoclasts are normal cells, which just happen to be in the wrong place at the wrong time! The odontoclasts basically eat their way into the tooth exposing the dentinal tubules.


Dentine exposure is extremely painful and, inexplicably, tertiary dentine is not produced to seal the exposed tubules as would occur with attrition. Eventually the lesion invades the pulp of the tooth. The process will continue and the root and crown become separated with, finally, loss of the crown.

FORL in a Cat


Clinical signs

  1. Pain, pain, pain = cranky cat (especially when oral examinations are attempted if the premolars are affected). These are the most painful conditions a cat can have – probing under GA usually makes the cat “jump”.
  2. “Chattering” especially after eating or drinking – acute dental pain.
  3. Gingival hyperplasia in a cat (this will be granulation tissue growing up over the lesions in an attempt to protect the sensitive tooth).
  4. In advanced lesions, a pinkish discolouration to the tooth – granulation tissue within the tooth structure.
  5. Heavy calculus burden on ONE side of the mouth only – the cat is avoiding pain by not using the affected teeth (usually only evident if lesions on 1 side)



In Australia, Stephen Coles reported in his 1990 survey that the overall prevalence of FORLs in 64 cats examined was 52%. If the cats were assessed according to age, 74% of cats over 6 years of age had lesions compared to 16% of cats less than 6 years of age. Overseas studies have found similar prevalences. The lesions have been found in captive and wild large cats (lions etc.).


All authors report that the prevalence of the disease has increased in the last 10 to 20 years. I doubt that this is true if looked at realistically.


These authors have not considered two important points. The first is that wild and feral cats rarely live beyond 5 years of age (as shown by the recent study in Kakadu). One would only expect the prevalence in these cats to be low. Even domestic cats had relatively short life spans up to 20 years ago. The improvements in nutrition and disease control have altered this.


The second point for consideration is our ability to recognise and diagnose FORLs. How many veterinarians would have (in years past) attempted to probe under areas of gingival hyperplasia (if they recognised that) to check for lesions? How many would have radiographed those slight “bumps” in the gum where teeth are missing (and found tooth roots)?


I have no doubt that the actual prevalence is increasing but that it is not due to something in the diet etc., just our ability to keep cats alive long enough for them to get some FORLs combined with our new found diagnostic skills which allows us to find them!




There is currently only one effective treatment for FORLs once diagnosed – extraction.


This extraction is difficult and time consuming. Teeth with FORLs are very brittle and fracture easily if excessive force is used. If there is NO evidence of periodontal disease associated with the tooth, crown amputation can be used successfully. The root will continue to resorb as the process has already started. This must not be done if any infection is present as the root can act as a nidus for further problems.


Many veterinarians have attempted to restore these FORLs with glass ionomers etc. similar to caries. The lesion is progressive in spite of this and, if these cats are followed up, the FORL will continue under the restoration and the tooth eventually lost.


- Dr Gary Wilson © 2000


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