How vets grade dental disease in dogs and cats

Why grading matters

Dental disease is very common. The AAHA 2019 Dental Care Guidelines note that by three years of age, most dogs and cats have some level of periodontal disease, and that it often goes unnoticed by owners. Much of it sits below the gumline, out of sight. Grading turns “his teeth look a bit dirty” into a clear record of which teeth are affected, how badly, and what each one needs. It also lets your vet compare one visit with the next.

How a mouth is assessed

• An awake exam. A first look at the face, gums and visible tooth surfaces. It is good for spotting tartar, red gums, broken teeth and swelling, but it cannot measure what is happening under the gum.
• Probing under anesthesia. With your pet asleep, a thin, blunt probe is slipped gently into the small pocket around each tooth. AAHA recommends checking six sites per tooth. Normal pockets are shallow: about 1–3 mm in dogs and 0.5–1 mm in cats, according to the Merck Veterinary Manual. Deeper pockets suggest the tissues that hold the tooth in place have been lost.
• Dental X-rays. Full-mouth radiographs show the roots and jawbone. Both AAHA and the Merck Veterinary Manual recommend them, and in cats they are needed to diagnose tooth resorption.

Because the full picture only appears after probing and X-rays, the final treatment plan is usually confirmed during the anesthetized procedure. This is also why the AAHA and WSAVA dental guidelines do not support anesthesia-free cleaning: it can make teeth look whiter without treating, or even seeing, disease below the gumline.

Periodontal disease stages: PD0 to PD4

The American Veterinary Dental College (AVDC) stages periodontal disease for each tooth, based on how much of the tooth’s support (its “attachment”) has been lost:

• PD0 – Clinically normal. No visible gum inflammation or periodontitis.
• PD1 – Gingivitis only. The gums are inflamed, but no support has been lost.
• PD2 – Early periodontitis. Less than 25% of the attachment is lost, or there is early bone loss between the roots of a multi-rooted tooth (furcation stage 1).
• PD3 – Moderate periodontitis. 25–50% of the attachment is lost, or furcation stage 2.
• PD4 – Advanced periodontitis. More than 50% of the attachment is lost, or furcation stage 3.

What this means for you: gingivitis (PD1) can usually be reversed with a professional cleaning and good home care. Once support has been lost, the Merck Veterinary Manual notes that periodontitis is not as easily reversible, so the goal becomes stopping it from getting worse. Teeth at the advanced stages are more likely to need oral surgery, which your vet will talk through with you.

Other scores you may see

• Plaque and calculus (tartar) indices. Simple 0–3 scores for how much of the tooth is covered, from none to heavy.
• Gingival index. A 0–3 score for gum inflammation.
• Furcation (F1–F3). How far a probe passes into the space between the roots: less than halfway (F1), more than halfway (F2), or right through (F3).
• Mobility (M0–M3). How loose a tooth is, from normal (M0, up to 0.2 mm of movement) to more than 1 mm, or any movement up and down into the socket (M3).

“Grade 1–4” versus AVDC stages

Some clinics, and many older reports, describe the whole mouth with a single “Grade 1–4” dental disease label, often based on what can be seen. It follows a similar mild-to-severe pattern, but it is a summary rather than the AVDC system. The AVDC uses “stage” for how far a progressive disease has advanced, and assigns it to each tooth after probing and X-rays. One pet can have healthy teeth right next to a PD4 tooth, so a single grade can hide important detail. If your report uses grades, it is always fine to ask which teeth are most affected.

Dogs and cats at a glance

Cats: tooth resorption

Tooth resorption is a condition in which the body breaks down the structure of a tooth. Cornell’s Feline Health Center estimates it affects 20–60% of all cats and close to three-quarters of cats aged five and older, and the cause is still unknown. The AVDC stages it from TR1 (mild loss of the outer layer) through TR4 (extensive damage) to TR5 (only root remnants are left under healed gum). On X-rays it is also typed: T1 (focal), T2 (the root is being replaced by bone-like tissue) or T3 (features of both). Stage and type help your vet decide on treatment. Cornell notes that removing affected teeth is generally the only effective treatment.

Cats: chronic gingivostomatitis

Feline chronic gingivostomatitis is severe, long-lasting inflammation of the gums and the lining of the mouth, often reaching the back of the mouth. Cornell describes it as relatively uncommon but very painful, with the immune system over-reacting to plaque. Treatment can involve medication, extractions, or both, and is tailored to each cat.

Dogs: crowded mouths and broken teeth

The WSAVA guidelines note that small and toy breed dogs are particularly susceptible to periodontal disease, and the Merck Veterinary Manual lists tooth crowding as a risk factor. Dogs also break teeth, often on hard objects such as real bones, antlers, hooves, hard nylon toys, rocks or cages. The AVDC separates an uncomplicated crown fracture (no pulp exposed) from a complicated one, where the pulp (nerve) is exposed. An exposed pulp may look like a red or dark dot on the broken surface; that tooth needs treatment, usually root canal therapy or extraction. Many dogs keep eating as usual despite the pain.

What you can do, and when to book

Brushing daily, or at least every other day, is the most effective home care, according to the Merck Veterinary Manual. Plaque left for more than two days can harden into tartar that brushing cannot remove. Our guide to brushing and at-home dental care has practical tips.

Book a dental check if you notice bad breath, red or bleeding gums, tartar, a broken or loose tooth, facial swelling, drooling, or changes in how your pet eats. It is also worth booking if it has been a year or more since your pet’s last oral exam.

Nomad Pet Dental brings dental care for cats and dogs to your home, including exams, dental X-rays, cleanings under anesthesia and extractions. If you have questions about your pet’s mouth or a past dental chart, book an appointment or call (720) 839-8885.

This article is general information, not a diagnosis. Every pet is different, so please talk to a veterinarian about your own pet’s teeth.

Sources

• American Veterinary Dental College (AVDC), Nomenclature
• AAHA, 2019 AAHA Dental Care Guidelines for Dogs and Cats
• Niemiec B. et al., World Small Animal Veterinary Association Global Dental Guidelines, Journal of Small Animal Practice, 2020
• Merck Veterinary Manual, Periodontal Disease in Small Animals
• Merck Veterinary Manual, Endodontic Disease in Small Animals
• Merck Veterinary Manual, Dental Development of Dogs and Dental Development of Cats
• Cornell Feline Health Center, Tooth Resorption and Gingivostomatitis
• Today’s Veterinary Practice, Algorithm for the Diagnosis and Treatment of Fractured Teeth