Here is the short version: there is a common dental disease in cats where the body's own cells slowly eat away the tooth, often starting in a place you cannot see. It is painful, most cats hide it and keep eating, and by old age the majority of cats have it. The hard truth is that nobody has worked out what causes it or how to prevent it. The useful truth is that it can be found and treated, and finding it early spares a cat a lot of quiet suffering. This guide explains what it is, why it stays hidden, and what actually helps.
Most older cats have it
Tooth resorption, once called feline odontoclastic resorptive lesions or "neck lesions," is one of the most common dental problems in cats. Cornell's feline center estimates it affects roughly 20 to 60 percent of all cats, and close to three-quarters of cats aged five and older.1 The Merck veterinary reference puts it simply: more than 60 percent of cats will show evidence of tooth resorption in their lifetime.2
Cornell Feline Health Center, 2024
The wide range in those numbers is itself a clue. How many cats are counted as affected depends heavily on their age, their breeding, and crucially on whether anyone took dental X-rays, because a lot of the disease lives below the gumline where the eye cannot reach. One colony study of 109 cats found resorption in 70 percent of purebred cats versus 38 percent of mixed-breed cats, and that most of the lesions were of the deeper, root-replacing type.4
What "resorption" actually means
In a healthy mouth, specialized cells remodel teeth and bone in a slow, controlled way. In tooth resorption that process goes wrong on a specific tooth, and cells begin to destroy the hard tissue of the tooth itself, eroding the enamel, the dentin underneath, and sometimes the root. The tooth is literally being dissolved and, in late stages, replaced by bone. It is progressive, and once it has started on a tooth it does not heal or reverse on its own.2
This is why it matters so much that the damage often begins out of sight. Early lesions can sit at or below the gumline, where a glance into the mouth, even by an attentive owner or a vet during an awake exam, will miss them entirely.
Why it hurts so much, and why you would never know
Resorption exposes the sensitive inner tooth, and it is genuinely painful. Cornell describes cats that flinch in clear pain when an affected tooth is touched.1 Yet the same source notes that the condition usually has to reach an extreme level before a cat will actually stop eating.1 Cats are built to conceal weakness, so they swallow food whole, chew on the other side, or favor soft food, and most owners read none of that as a dental emergency.
The two types, and why the difference matters
Veterinary dentists sort tooth resorption into types based on what an X-ray shows, because the type changes the right treatment.3 In Type 1, the root still looks normal and distinct on the film, with the thin ligament space around it intact. In Type 2, that ligament space is fading and the root is being resorbed and fused into the surrounding bone, so the root starts to look like a faint ghost on the X-ray. Some teeth show features of both.
That distinction is not academic. A Type 1 tooth has a real root that must be fully removed. A Type 2 tooth, where the root is already dissolving into bone, is sometimes treated with a different technique called crown amputation, but only when an X-ray confirms it is genuinely Type 2 and there is no gum infection, root-canal disease, or stomatitis.2 You cannot tell these apart by looking. You can only tell with a radiograph.
Nobody knows what causes it
This is the honest and slightly unsatisfying center of the topic. Despite decades of study and many theories, the cause of feline tooth resorption is not known. Merck states it plainly: there is no identified cause for the idiopathic form that affects multiple teeth in cats.2 Cornell agrees that the trigger is simply unknown.1 We are not going to pretend otherwise, because guessing would be the opposite of what this site is for.
That unknown cause has a direct, practical consequence, and it is the most important sentence in this article: because we do not know what starts it, we cannot prevent it. Brushing, which genuinely helps prevent gum disease, has not been shown to stop tooth resorption.
Why your vet needs X-rays and anesthesia
Since the disease hides below the gumline, the only reliable way to find and grade it is with full-mouth intraoral dental X-rays, taken under anesthesia.1 Anesthesia is not an upsell here. It is the only way to position X-ray sensors correctly, probe each tooth, and clean below the gumline in an animal that will not hold still for any of it. The 2025 feline dental care guidelines treat an anesthetized oral exam with full-mouth radiographs as the standard of care precisely because so much disease lives where you cannot see.7
What treatment looks like
There is no filling, bonding, or medicine that saves a resorbing tooth. The process cannot be reversed, so the accepted treatment is surgical extraction of the affected tooth, which removes the source of the pain.2 In the specific Type 2 cases described above, a veterinary dentist may instead amputate the crown and leave the already-dissolving root, but that is a careful, X-ray-guided decision, not a shortcut. The good news in all of this is concrete: once the sore tooth is gone, the pain goes with it, and cats very often perk up in ways their owners did not expect.
The rest of the feline mouth: gum disease and stomatitis
Tooth resorption shares the mouth with two other common problems worth knowing. The first is periodontal (gum) disease, which is widespread in cats just as it is in dogs. A large UK primary-care study found periodontal disease to be the single most commonly diagnosed disorder in cats, and unlike resorption, this one does respond to the prevention you would expect.5 The same daily-care logic from our dog dental disease guide applies: brushing and products carrying the VOHC seal help control the plaque that drives gum disease.
The second is feline chronic gingivostomatitis, a severe, immune-mediated inflammation of the mouth that is far less common, found in under 1 percent of cats in first-opinion practice, but miserable for the cats who have it.6 It often needs full-mouth or near-full-mouth extractions to bring relief, which surprises owners but frequently works when medication alone has failed.
What to do this week
- Watch how your cat eats. Chewing on one side, swallowing kibble whole, dropping food, drooling, or a new preference for soft food are all worth mentioning to your vet.
- If your cat is middle-aged or older and has never had dental X-rays, ask your vet about a full dental assessment under anesthesia, which is the only way to find resorption.
- Do not be talked out of the X-rays or the anesthesia. For this disease, an awake look in the mouth is not enough.
- For everyday dental health, start gentle toothbrushing or a VOHC-accepted product to fight the gum disease you can prevent, even though it will not stop resorption.
Tooth resorption is a frustrating disease to write about honestly, because the usual reassuring line, "here is how to prevent it," does not exist yet. What does exist is a cat who is quietly hurting and a clear way to find and fix it. For an animal that will never tell you its tooth aches, a dental X-ray is how you hear it.