Feline Odontoclastic Resorptive Lesions

Feline Odontoclastic Resorptive Lesions

Common Dental Issue Often Goes Undiagnosed

Jennifer Hawkins, DVM

You might think a veterinarian always knows when something abnormal is going on in their pets. It’s true;We’re able to examine our pets from home, but I admit that I don't do this on a regular basis. When I'm home, my pets expect me to serve them, and I expect them to supply me with entertainment and heaping amounts of love in return.

It occurred to me during a recent head-rubbing marathon that my pets were due for their annual examinations. While I had my cat Mottley on her back, I pushed back her checks and took a look at her teeth. And there it was: a resorptive lesion in her mouth. Darnit, I thought, why didn't she tell me? Why hadn’t I, of all people, scheduled her annual dental exam on time?

What is a Resorptive Lesion?

A resorptive lesion is a dental abnormality technically referred to as feline odontoclastic resorptive lesion (FORL), or more recently as tooth resorptions (TRs). These lesions develop at the cat’s neck or at the base of a tooth and are similar to cavities. While occasionally seen in dogs, they occur very frequently in cats.

Tooth resorptions involve the activation of cells called odontoclasts which eat away normal bone cells of the teeth. The result is a hole in the tooth that looks like a red dot at the base. Typically these lesions are challenging to see as the gum tissue usually grows over the lesion as an attempt to protect the area.

According to , Brook A. Niemiec, DVM, a boarded specialist in veterinary dentistry, there are three types of TRs: Type 1, 2 and 3.

- Type 1 lesions have resorption of the root; the root canal and periodontal ligaments are normal.

- Type 2 lesions have replacement resorption, when there is resorption of the root canal and periodontal ligament. In advanced type 2 lesions, the cat's tooth will basically end up with nothing left as it has been taken over by bone.

- Type 3 lesions are essentially, explains Niemiec, a combination of Types 1 and 2.

What Causes Tooth Resorptions?

While there are several theories being investigated about the cause of TRs, there are no clear answers at this time. What we do know is that inflammation caused by dental disease is often a factor. Tooth resorptions are the most common dental problem in cats and purebred cats seem to be at a greater risk for developing them.

Are Tooth Resorptions Painful?

Yes, TRs do cause pain. In fact, when a dental probe is gently placed on the lesion, cats typically "chatter" or vibrate their jaws which is an obvious sign of pain. Some cats may show decreased appetite, pawing at the mouth, drooling, or weight loss.

However, as was the case with my cat Mottley, there are usually no outward signs that a TR is present. Surprisingly, most animals continue to eat quite normally even when severe dental disease is present.

How are Tooth Resorptions Diagnosed?

Most often, TRs can be noted on routine physical exam; however, sometimes they aren't apparent unless the cat is already anesthetized for a dental exam and cleaning.

How Are Tooth Resorptions Treated?


The average cost of treating feline odontoclastic disease, as revealed by policyholder claims filed in 2013, 

is $382. Treatment for most Type 1 and Type 2 TRs at this time is extraction of any affected teeth. If not extracted, the tooth will continue to erode and be a constant source of pain for the cat. In some cases, restorative procedures can be performed to save a tooth that is in an early stage of the disease.

Advanced Type 2 TRs and Type 3 TRs can be treated with a newer procedure called crown amputation. During a crown amputation, the tooth is cut at the crown, after which the remaining bone is smoothed and then closed over with a gum flap. According to Niemiec, a crown amputation is "much less traumatic than digging after a root that no longer exists." Healing time is also faster for the cat.

Niemiec, who teaches other veterinarians how to perform crown amputations, lists the mandatory requirements that must be met prior to the procedure:

  • Confirm Type 2 lesion through a radiograph;
  • See no evidence of a root canal on radiographs;
  • See no evidence of a periodontal ligament on the radiograph;
  • The cat shows no evidence of periodontal disease;
  • The cat shows have no evidence of endodontic disease; and
  • The cat is not being treated for caudal stomatis (inflammation of the oral cavity).

My cat Mottley eventually had many teeth extracted over the years due to TRs. It may sound drastic, but it's the only effective way to remove the source of pain and infection. It may surprise you that animals with little or no teeth usually eat their food quite normally. However, if teeth have recently been extracted, I recommend temporarily feeding soft food or moistening kibble for a few days if your pet is used to eating a dry diet.

If you notice any symptoms that your cat’s teeth may be causing him pain, don’t wait—please schedule an appointment with your veterinarian for a thorough oral exam.