Vancouver Feline Hospital - Cat Veterinary Clinic

Feline Odontoclastic Resorptive Lesions (FORLs)

These are the major reason for spontaneous and dentist-assisted tooth loss in the cat. Basically what happens is that the tooth develops a cavity at the gum-line, this gets bigger and the crown of the tooth is lost. The roots of the tooth get resorbed (become like bone). We think that this is painful because the pulp cavity is exposed, and affected cats react unpleasantly if the affected tooth is touched.

The lesion begins to form within the tooth and breaks out at the neck. Which tooth is affected is due to a normal anatomical difference in the cementum of that tooth that seems to make the site susceptible to expressing the lesion. A cat may have this anatomical variation in one or many teeth and therefore will develop one or multiple lesions while a littermate may have another, also normal, arrangement of its cementum at the neck and therefore has healthy teeth. The rough cemental surface in the neck area then accumulates plaque and bacteria and the gingivitis is secondary. So cat genetics has a role to play.

Genetics combined with subtle vitamin and mineral deficiencies may be the real reason. Mummified cats in Egypt show these cavities; they were documented in the literature in the 1930's, and isolated feral cat colonies (natural diet) have these cavities; so it is hard to blame our modern diets. Suspicion is now falling on vitamin D excess - hypervitaminosis D causes similar lesions in laboratory animals. We know that humans, dogs, chinchilla, guinea pigs and marmosets also get these lesions. We know that cats do not synthesise vitamin D3, they depend on diet to supply this essential need. Twenty out of 49 canned diets were found to contain in excess of 30 times the vitamin D3 requirements. Just about everything, including canned food, water, and conspiracy theories have been blamed for this problem! Cats fed only dry food also develop these lesions.

We see this problem in mainly older cats - early teens (late teens they often have advanced periodontal disease) - with or without signs of early kidney insufficiency. It is worth testing for early kidney insufficiency (a microalbuminuria test) in these cats. The kidneys play a major role in calcium metabolism (the delicate balance between calcium, phosphorous and vitamin D).

The first sign of a FORL is a spot of redder, thicker gum on a tooth. Then the gum tries to fill the forming cavity, and then we can clearly see the cavity eating away at the crown.

Dental cleaning, extraction and antibiotics are ESSENTIAL if there are signs of infection present (bad breath, whitish discharge or discoloured plague) on basic examination.

If the dentist can find the lesion it is already too big to treat. Restoration is mostly unsuccessful - this is an interior problem and plugging it doesn't help. Extraction is strongly recommended, in most cases. The dentist needs dental x-rays to properly evaluate these teeth. X-rays will show one of two things:

1. There is no radiographic evidence of infection, inflammation and the roots are "resorbing" (becoming part of the jawbone) - these roots do not come out easily, and to avoid unnecessary trauma and bone loss, the dentist will remove only the crown of the tooth.
2. But if x-rays indicate any infection or problem, the whole tooth including the roots must be extracted. Those roots will not resorb.
3. If the gums are already closed over the tooth, and no infection or protruding spicule of tooth is present, the dentist will also prefer not to remove the roots and leave well alone.

Sadly, early disease processes may not be visible on x-rays at the time, so the dentist will want to check the healing process about 1 week and also within six months of the surgery. Follow-up radiographs about 6 months post surgery are necessary to finish the evaluation of the extracted teeth, to know for certain no infection is present at the roots that remain.

It is important that you are aware if roots have been left in; and we suggest you request a copy of your cat's dental record and dental x-rays to keep with your copy of your cat's medical history.

Experimental work is under way using biphosphonate compounds to decrease the progression of this resorptive process. It seems some feline lesions actually repair under treatment. These drugs are not cleared for animal use (they are prescribed for osteoporosis).