There is a dental disease that affects somewhere between a fifth and two-thirds of all cats, causes pain that vets describe as excruciating, and almost never announces itself. It has no smell, no obvious swelling, and in its early stages nothing you could spot by lifting a lip. Most of the destruction happens below the gumline, on the root, where you cannot look. By the time an owner notices anything, the visible part of the problem is often the last part of it to appear.

The condition is tooth resorption. You may have heard the older names — feline odontoclastic resorptive lesion, or FORL, and cervical line lesion. They describe the same process, and the process is strange enough to be worth understanding: the cat's own cells dismantle the cat's own tooth.

What Tooth Resorption Actually Is

Inside every tooth is a chamber containing blood vessels, lymphatics, and nerves, surrounded by dentin, the hard substance that makes up the bulk of the tooth. In tooth resorption, that mineralized tissue — enamel, dentin, and the cementum covering the root — is progressively destroyed and eventually lost.

The demolition crew is a population of cells called odontoclasts, which are all but identical to the osteoclasts that remodel bone throughout the body. Under normal conditions this machinery is useful; it is how kittens shed their baby teeth. In tooth resorption it switches on where it should not, and does not stop. The process typically begins with a breakdown of the normal periodontal ligament architecture and focal damage to the cementum on the root surface. Small areas of root resorption often quietly repair themselves. When repair fails, the resorption advances into the dentin and travels upward toward the crown, undermining the enamel from beneath until a visible defect finally appears at the neck of the tooth. Frequently, bone or cementum grows in to replace what was lost — the tooth is not just eroded but substituted.

This is not a cavity. Cats do not get cavities in the human sense. It is not a bacterial hole drilled inward from the surface; it is a resorption front moving outward from the root.

How Common It Is

Estimates vary with the population studied and how carefully investigators looked, but the numbers are consistently high. The Cornell Feline Health Center puts it at 20 to 60 percent of all cats, and close to three-quarters of cats aged five and older. The Merck Veterinary Manual reports that more than 60 percent of cats will show evidence of tooth resorption at some point in their lives, with incidence rising in older cats and in purebreds.

The mandibular third premolar — the first cheek tooth on the lower jaw — is often the first affected, and the left and right mandibular third premolars are the teeth involved most often overall. Lower premolars and molars carry the bulk of the disease.

The Cause Is Still Unknown

This is the frustrating part. Despite decades of investigation, there is no identified cause for the idiopathic form that affects multiple teeth in otherwise healthy cats. Inflammation from periodontitis is known to drive resorption in areas of periodontal disease, so gum disease explains some cases — but not the widespread, multi-tooth pattern that shows up in cats with clean-looking mouths.

Excess dietary vitamin D has been the leading hypothesis for years, and it remains unresolved. As Dr. Jennifer Rawlinson, formerly chief of dentistry and oral surgery at Cornell, put it: some researchers theorize that an excess of vitamin D in commercial cat food might be to blame, others disagree, and for now there is no answer. Confusingly, low serum vitamin D has also been linked to a higher prevalence of multiple lesions, so both deficiency and excess may matter in ways nobody has untangled.

Other threads under investigation include cytokine-mediated odontoclast activation, matrix metalloproteinase-9 expression, shifts in the oral microbiome, and craniofacial anatomy. A study published in Animals in January 2026, reviewing 166 radiographically confirmed cases, found that brachycephalic cats — flat-faced breeds like Persians — were significantly younger than non-brachycephalic cats at diagnosis yet already had more advanced Stage 4 lesions. It also found that chronic gingivostomatitis, while more common in non-brachycephalic cats, was not associated with resorption severity. These are associations in a single retrospective sample, not proven causes, but they point toward skull conformation as a factor worth watching.

One genuinely humbling data point: archaeological evidence shows tooth resorption in cats as far back as the 13th and 14th centuries. Whatever drives it, it is not new and it is not simply a product of modern kibble.

The Signs Cats Actually Show

Cats are exceptional at concealing oral pain, and the classic image of a pet with a toothache — off its food, drooling, pawing at its face — is misleading here. Chronic, obvious toothache behavior is not among the most reliable signs. What owners tend to notice instead is subtler and easy to dismiss:

An affected tooth can produce a dramatic reaction when touched — a cat may flinch, jaw-chatter, or cry out when a vet's probe finds the lesion, even under light sedation. Appetite loss usually only arrives at the extreme end, or abruptly if a weakened crown fractures off, in which case a cat may stop eating for 24 to 72 hours. Notably, lesions confined to the root, with nothing exposed to the mouth, are thought to be relatively painless. Pain arrives when the defect breaks through into the oral cavity and exposes dentin and nerve.

Diagnosis: Why Radiographs Are Not Optional

A conscious lip-lift exam catches some lesions and misses many. Two tools do the real work.

The first is the dental explorer, the sharp-tipped end of a periodontal probe, run carefully along the cementoenamel junction of each tooth. Early lesions confined to enamel or cementum are invisible on radiographs — they have not removed enough tissue to show up — so they are found by feel, sometimes with the help of surgical loupes. Lesions hidden just under the free gingival margin are found the same way.

The second is full-mouth intraoral dental radiographs, which is why proper dentistry requires general anesthesia. Radiographs are the only way to determine how far the disease has gone below the gumline and what kind of resorption it is — and both of those answers change the treatment. Cone-beam CT is more accurate still where it is available.

Stages and Types, and Why the Difference Matters

The American Veterinary Dental College classifies lesions two ways at once. Stage (1 through 5) describes how much tooth has been lost: Stage 1 involves only cementum or cementum and enamel; Stage 2 reaches dentin but not the pulp; Stage 3 reaches the pulp cavity while the tooth largely holds together; Stage 4 means substantial crown or root destruction with loss of structural integrity; Stage 5 is little more than irregular fragments of hard tissue under fully healed-over gum.

Type (1 through 3) describes what the periodontal ligament space looks like radiographically. Type 1 shows a focal radiolucency with an otherwise normal-density tooth and a normal ligament space — inflammatory resorption. Type 2 shows the ligament space narrowed or gone entirely, with the root fading into "moth-eaten" or ghost-like radiolucency as it fuses with surrounding bone. Type 3 has features of both in the same tooth.

The distinction is surgical. A Type 1 tooth still has an intact ligament and a real root, so it must be extracted completely. A Type 2 root has already been partly replaced by bone and may be impossible to remove intact — attempting it can mean substantial trauma to the jaw. For radiographically confirmed Type 2 lesions, in the absence of periodontitis, endodontic disease, or stomatitis, vets may perform crown amputation with intentional root retention, removing the painful crown and leaving the already-resorbing root to finish being absorbed. Done for the right tooth, this is good medicine. Done for a Type 1 tooth, it leaves a live root behind and the cat still in pain. That is the entire argument for radiographs.

Treatment, and What Cannot Be Done

Teeth affected by resorption and exposed to the oral environment are extracted. There is no filling, no sealant, no drug that halts the process; fillings placed over resorptive lesions fail because the resorption underneath continues. Treatment is aimed squarely at removing the source of pain.

Where inflammation from marginal periodontitis is driving the resorption, good oral hygiene can slow the destruction — which is a real argument for brushing, dental checks, and professional cleanings. But idiopathic tooth resorption cannot currently be prevented, because nobody knows what to prevent.

Owners are often surprised by how well cats do after extractions, including multiple ones. Cats that had been quietly guarding a mouth for months frequently become more active, more affectionate, and better eaters within a couple of weeks, and most manage dry food perfectly well with fewer teeth. The most common comment vets hear afterward is that the cat seems younger.

What to Do Now

Have your cat's mouth examined by a vet at least once a year, and ask specifically about the cementoenamel junction and resorptive lesions rather than accepting a general "teeth look okay." If a lesion is suspected, dental radiographs under anesthesia are the appropriate next step, not a wait-and-see. And once a cat has confirmed tooth resorption anywhere in its mouth, annual anesthetized exams with full-mouth radiographs become the standard of care — the disease is progressive, other teeth are usually next, and catching the next lesion early is far kinder than catching it at Stage 4.

If your cat has started swallowing kibble whole, drifted toward wet food, or begun chewing on one side, that is not fussiness. It is worth a phone call.