Cat Tooth Resorption Types 1, 2, and 3: AVDC Classification Explained

Last updated: May 23, 2026

Why the Three Types Matter

Feline tooth resorption (TR) — historically called FORL — is not a single disease. The American Veterinary Dental College (AVDC, avdc.org) classifies resorption into three radiographic types, and the type drives the recommended treatment. Type 1, Type 2, and Type 3 are not “stages” or progressive grades; they are distinct radiographic patterns that can occur independently in different teeth of the same cat at the same time.

This article explains each type in plain language, what it looks like on dental radiographs, and what the AVDC-aligned treatment is. None of this can be determined from a visual oral exam alone — type classification requires dental radiographs under anesthesia. See our overview of cat dental cleaning anesthesia protocols for what that procedure involves.

How Veterinary Dentists Determine the Type

Once the cat is under general anesthesia, full-mouth intraoral dental radiographs are taken. The veterinarian or AVDC diplomate evaluates each affected tooth for two features: periodontal ligament space (the dark line on radiographs between the tooth root and the surrounding alveolar bone) and root structure integrity (whether the root looks normal, partially intact with patchy resorption, or essentially replaced by bone).

Those two features sort each lesion into Type 1, Type 2, or Type 3. The type matters because the surgical approach differs substantially — for some types, complete extraction is mandatory; for others, a less invasive procedure is acceptable.

Type 1: Inflammatory Resorption

Type 1 lesions are characterized by intact, clearly visible roots on dental radiographs and a clearly preserved periodontal ligament space. The resorption is happening on the tooth surface, often at the cervical (neck) region, and is typically associated with concurrent periodontal disease — inflammation, plaque, calculus, gingivitis around that tooth.

Because the root remains intact, Type 1 lesions require full extraction with complete root removal. Leaving any root fragment behind risks ongoing pain and infection. The surgical approach is conventional: flap creation, sectioning of multi-rooted teeth, careful elevation, and removal of all root tissue with verification by post-extraction radiograph.

Type 1 lesions often suggest that broader periodontal disease is part of the picture. See our overview of periodontal disease staging in cats for the AVDC PD0-PD4 staging framework.

Type 2: Replacement Resorption

Type 2 is the resorption pattern that has reshaped feline dental treatment over the past two decades. In Type 2 lesions, the tooth root is being replaced by bone-like material. On dental radiographs, the root appears indistinct — the periodontal ligament space is lost, and the boundary between root and surrounding bone is blurred or absent. The crown remains clinically visible but the root is essentially fusing with the jaw.

For Type 2 lesions, full extraction of the root would be both extremely difficult and unnecessarily traumatic — the surgeon would essentially be removing jawbone. The AVDC accepts crown amputation with intentional root retention as a legitimate treatment for Type 2 lesions. The crown is removed surgically; the resorbing root remnant is left in place to continue its biologic replacement by bone.

Crown amputation is not appropriate in every case. Pre-conditions include: confirmed Type 2 radiographic appearance, no clinical periodontal disease at that tooth, no endodontic involvement, and no overlying soft-tissue infection. If any of those conditions are not met, full extraction is preferred.

Type 3: Mixed Type 1 and Type 2 Features

Type 3 lesions have features of both Type 1 and Type 2 in the same tooth — typically with the buccal (cheek-side) root showing Type 2 replacement resorption while the lingual (tongue-side) root retains a more normal radiographic appearance, or vice versa.

Treatment depends on the radiographic appearance. Roots that look like Type 1 (intact, clearly visible) should be fully extracted. Roots that look like Type 2 (replaced by bone) can be managed with crown amputation. In practice, this often means a mixed approach to a single multi-rooted tooth.

Stage Versus Type: Two Different Classifications

The AVDC also uses a stage classification (Stage 1 through Stage 5) that describes how far the resorption has progressed in the structure of an individual tooth — early enamel involvement, dentin involvement, pulp exposure, severe crown destruction, and tooth lost with only gingival covering remaining. Stage and Type are independent. A tooth can be Stage 4 Type 1 (advanced inflammatory resorption with crown destruction but intact roots), or Stage 3 Type 2 (moderate replacement resorption), or any combination.

For an adopter, the practical takeaway is that your veterinarian will use both stage and type to plan the procedure. You do not need to memorize every combination — but knowing the type system exists helps you ask informed questions.

Why You Cannot Type a Lesion From a Photograph or Awake Exam

A cat dentistry social media post or an awake oral exam can identify that a lesion is present — but cannot reliably identify which type it is. The differentiation between Type 1 and Type 2 lives in the radiographic appearance of the root, and the root is hidden beneath the gum line. Anesthesia-free dental claims cannot deliver radiographs, which is one of several reasons the AVDC opposes them.

If a clinic identifies tooth resorption but cannot take dental radiographs, referral to an AVDC-credentialed practice or a primary-care clinic with imaging is the appropriate next step.

What This Means for Treatment Planning

The practical treatment-planning sequence at an AVDC-aligned clinic looks like:

1. Pre-anesthetic blood work and exam by your primary veterinarian.
2. General anesthesia with ACVAA-aligned monitoring.
3. Full-mouth intraoral dental radiographs.
4. Lesion-by-lesion type classification.
5. Treatment per lesion: full extraction for Type 1, crown amputation for Type 2 (when criteria met), mixed approach for Type 3.
6. Post-extraction radiographs verifying complete treatment.
7. Local nerve blocks, post-op pain medication, recovery plan.

This sequence is what defines modern feline dental care.

Recovery Looks Similar Regardless of Type

Whether your cat had a Type 1 full extraction or a Type 2 crown amputation, the recovery experience is generally similar: soft food for several days, oral pain medication, gentle monitoring for unusual drooling or pawing at the mouth, and a recheck appointment. See cat tooth extraction recovery for the typical timeline. Most cats are eating well within a week and many show notable behavior improvements once chronic dental pain is gone.

What You Can Do at Home

None of the home-care tools — brushing, dental chews, water additives — prevents tooth resorption (the cause is idiopathic; see our FORL overview). But all of them help with periodontal disease, which sometimes co-exists with Type 1 resorption. Daily brushing remains the home-care gold standard for periodontal disease.

Working With AVDC and Your Primary Veterinarian

For most cats, your primary AAFP-aligned or Cat Friendly Practice veterinarian (catvets.com, catfriendly.com) is well-equipped to diagnose and treat tooth resorption. For complex multi-tooth cases or cases with concurrent stomatitis, refer to an AVDC diplomate. The AVDC directory is at avdc.org. Severe cases with extensive disease may benefit from advanced imaging — see our cat tooth resorption overview.

If your vet does not perform full-mouth dental radiographs as a standard part of cat dental procedures, that is a reasonable conversation to have. The AVDC position is clear: tooth resorption cannot be diagnosed or properly typed without radiographs. Some practices charge separately for dental radiographs and may skip them when bundled cleanings are quoted on the cheaper end. Asking “will full-mouth radiographs be taken under anesthesia, and how will results affect the treatment plan?” is a fair and welcome question. A practice that responds well to this question is a practice that takes feline dental medicine seriously.

Frequently Asked Questions

Are Type 2 lesions really safe to leave roots behind?

Yes — when the radiographic criteria are met (clear Type 2 appearance, no periodontal disease, no endodontic involvement, no infection). AVDC has endorsed crown amputation with intentional root retention as legitimate treatment for confirmed Type 2 lesions for many years.

Can my cat have Type 1 and Type 2 lesions at the same time?

Yes. Different teeth in the same mouth often have different resorption patterns. This is exactly why full-mouth radiographs matter — your veterinarian needs to type each lesion individually.

Does the type predict how aggressive the resorption will be?

Not reliably. Both Type 1 and Type 2 can be slowly progressive or rapidly progressive depending on the tooth and the cat. Following with periodic dental radiographs is how the disease course is tracked.

Will more teeth become affected over time?

Often yes — many cats develop new resorptive lesions over years. This is one reason annual or biennial dental exams (with radiographs when appropriate) are recommended in adult and senior cats by AAFP / Cat Friendly Practice clinics.

Can my primary veterinarian do crown amputation, or do I need a specialist?

Many primary veterinarians are well-trained in crown amputation. For complex cases or when type classification is ambiguous, referral to an AVDC diplomate is appropriate.