"What are Feline Odontoclastic Resorptive Lesions (FORLs) ?

"What are Feline Odontoclastic Resorptive Lesions (FORLs) ?

Health & Safety

Feline Odontoclastic Resorptive Lesions (for ease called FORLs), are one of the most common reasons for dental pain in the cat. This Pets4Homes article is going to look at their causes and treatment, as studies indicate up to 60% of felines can be affected by this painful condition.

Just what is a FORL?

The lesions are also known by other names including Feline Cavities, Neck Lesions, or Root Resorptions. They are classed to how severe they become and how much they affect the tooth at each stage.

They are a progressive dental problem, meaning the problem will continue unless veterinary interventions take place. The lesions begin attacking the tooth almost next to the gum itself. It means the gum becomes very sore and inflamed. The lesions continue to break down the tooth bit by bit. They are classed in stages as follows:

  • Class 1: The hard-outer enamel of the tooth is broken down.
  • Class 2: The soft dentine of the tooth is attacked.
  • Class 3: The pulp cavity surrounding the nerve is damaged.
  • Class 4: The tooth breaks and leaves the root still in its socket.

These lesions will be uncomfortable for the cat, but from Class 3, the tooth breaking down will cause severe dental pain. The pulp cavity is very sensitive and without protection from dentine and the hard enamel, the nerve is easily exposed.

Why do they happen?

The exact cause is not known, although there has been research into them, it is still inconclusive. The research suggests a link with a larger amount of Vitamin D in the affected cat's diet, but this has still to be properly proved.

Some cats have been found to be a greater risk of FORLs, namely those with a chronic condition such as kidney or liver failure. Other risk factors are those cats who carry infection or viruses.

The best-educated guess, until research is conclusive, is an issue with the cat's immune system. The FORLs may be an abnormal response in the immunity, setting up an excessive inflammatory mechanism in the cells at the gums. The side effects in this response, start breaking down the teeth.

Good dental hygiene does seem to have some effect on the lesions. Regular brushing of the teeth is thought to reduce the bacteria around the gums, lessening the immune system response.

Research has also indicated that cats around 10 are at higher risk of FORLs, and longer cats, under the age of 4 are unlikely to be affected.

What do I look for in my cat?

There is one main symptom with FORLs, and that is the mouth being very uncomfortable when the cat eats. If the lesions are not recognised and treated, the pain becomes worse.

If their eating habits change, (which cat’s often do), looking out for these signs may help:

  • Slow eating - when they used to finish the food quickly.
  • Head tilted when eating - to try and stop the food touching the sore area.
  • Chewing on one side - again to keep the food from the affected gum line.
  • Not wanting to eat or walking away after a few mouthfuls.
  • Aggression, even in the most placid cat - especially when the side of the head is touched.
  • The cat just suddenly rules to chew (usually due to multiple lesions in the mouth).
  • The cat refuses to eat biscuits - even softer biscuits and will only touch wet food.

Unfortunately, you may not see any of these signs until there are multiple lesions, as cats are such stoic creatures and hide the pain.

How are the lesions diagnosed?

Often the way the cat is found to have these lesions is when they stop eating properly and are brought to a veterinary surgery for examination. If a cat is not eating one of the first places the vet will check is the mouth area, first simply giving a visual look at the teeth to see if there is any tartar build up or even bleeding gums.

If there are no apparent issues, the teeth are often pressed gently with a finger. This is when lesions can be apparent as the tooth may simply snap.

The problem with these lesions is that they are below the gum line, so can’t be readily seen.

They may only be clearly visible either during a routine dental - even a simple descale and polish or using x-ray.

Not all veterinary practices have specialised equipment that allows them to take dental x-rays, however, if the facility is used, it can locate any problems before dental surgery. The vet will be able to then avoid further damaging the tooth roots that are affected.

What treatment is there for a cat with FORLs?

The treatment depends on the severity of the lesions. In the early stages of the disease such as Class 1, gentle and careful, but regular brushing may make the condition manageable. Because of the nature of FORLs, it is not possible to stop the progression of the disease, but it can reduce the speed of tooth breakdown.

If the cat is being treated for other infections or diseases, such as renal disease, then the medication and treatment may also slow the progress of the lesions, but not stop them.

After Class 1 lesions the severity increases to the point, that the only usual course of action is tooth extractions. To ensure there is no further pain, the vet removing the toot must also remove the tooth roots. Failure to get the roots out will mean the lesions will continue - even under the gum once it has healed from the tooth being removed. If this happens the cat will still be in pain, when it puts bite pressure on the affected gums.


If your cat shows any difficulty with their eating or any dental problems, please speak to your vet urgently. As discussed, the earlier any problems are picked up and diagnosed, the better chance the vet has of slowing the process. If they have access to dental x-ray equipment, then the diagnosis can definitely be made easier.

Newsletter icon
Get free tips and resources delivered directly to your inbox.


Pets for StudWanted Pets

Accessories & services


Knowledge Hub


Support & Safety Portal
All Pets for Sale