Last updated October 20, 2026
Vets grade periodontal disease in dogs tooth by tooth, from PD0 (healthy) to PD4, by how much of the tooth's support has gone. Stage 1 is gingivitis, inflamed gum with no damage underneath, and it's the only stage that fully reverses. Stages 2 to 4 are periodontitis, where the ligament and bone holding the tooth are being lost. A stage 2 tooth has lost under a quarter of its support, stage 3 a quarter to a half, and stage 4 more than half.
From stage 2 on, most of the damage sits under the gum, so the stage can only be set with a probe and dental X-rays while your dog is under anesthesia. Home care matters at every stage, but its job changes. Our overview of dental disease in dogs covers the other problems a dog's mouth can have.
The stages at a glance
| Stage | What has happened | What you might see | What only the probe and X-rays show | What home care can do |
|---|---|---|---|---|
| PD0 | Healthy | Pink or pigmented gum lying flat on the tooth | A gum pocket no deeper than 2 to 3 mm in a mid-sized dog | Keep it that way |
| PD1 | Gingivitis, nothing lost yet | A red line at the gum edge, puffy gum, bleeding when brushed, bad breath | That the bone is still at its normal height | Reverse it, after a vet cleaning if there's tartar |
| PD2 | Under 25% of the support lost | Often much like stage 1 | Early pockets and bone loss | Stop a treated tooth getting worse |
| PD3 | 25 to 50% lost | Sometimes a receding gum or a root showing | Deeper pockets, and on back teeth a probe sliding more than halfway under the crown | Decide whether the tooth can be saved |
| PD4 | Over 50% lost | Sometimes a loose tooth or pus, sometimes nothing | Bone gone past half the root, and on back teeth a probe that may pass right between the roots | Protect the teeth left after extractions |
Each tooth gets its own stage, so one mouth can hold a healthy canine, a stage 2 incisor and a stage 4 molar. The American Veterinary Dental College (AVDC) also scores two things on their own. Furcation is the fork where a back tooth's roots split, and how far a probe slides into it shows how much bone has gone from between the roots. Mobility is how far a tooth moves. Up to 0.2 mm is normal, and a tooth that moves more than 1 mm, or moves up and down in its socket, gets the top grade.
Why the gums alone don't tell you the stage
Lifting your dog's lip shows you the gum and the crown. It doesn't show the root, and in dogs the roots are longer than the crowns (AAHA dental guidelines, 2019).
Bauer and colleagues (PLOS ONE, 2018) tested how far a look gets you. The researchers staged 89 dogs by looking in their mouths while awake, then the full exam under anesthesia, with probing and X-rays, gave the real stage. The awake look matched it in about 4 dogs in 10. Among the stages with bone loss it did worst at stage 2, where that loss begins, getting it right in under a third of dogs. Four of the 16 stage 2 dogs looked like stage 0 or 1.
It was a small study in dogs already booked for dental work, funded by two pet industry trade bodies. Queck and colleagues (2018) also found, in 114 dogs, that the awake exam underestimated how many had active gum disease and how bad it was. And the AAHA guidelines say probing for pockets should never be done on an awake dog. Your vet can only give a firm stage, and a firm estimate, once the X-rays have been read.
The stage decides the treatment, and so most of the bill. Every stage starts from the same base of anesthesia, X-rays and scaling, and our guide to dental cleaning costs shows what each stage adds on top.
Stage 1, gingivitis
Stage 1 is inflammation of the gum edge only. The bone is at its normal height and no attachment has been lost. AAHA lists the treatment as scaling, polishing and home dental care afterward. Once the plaque stays off, the gum heals.
In 52 miniature schnauzers whose tooth care had stopped, 51 had at least one tooth move on to periodontitis within 60 weeks (Marshall and colleagues, 2014). What gingivitis looks like, and how fast gums respond to brushing, is in our guide to gingivitis in dogs.
Stage 2, early periodontitis
At stage 2 the inflammation has reached the ligament and bone, and under a quarter of the tooth's support has gone. On a back tooth the probe may just start to slip into the fork between the roots. From the outside it can look like stage 1, or worse than it is, which is why the awake look so often missed it.
It can come early in small dogs. In a research colony of 50 Yorkshire terriers checked under anesthesia every 8 weeks, 98% already had at least one tooth at stage 2 at about eight and a half months old. The share of teeth affected rose from about a quarter to about half over the next ten months (Wallis and colleagues, BMC Veterinary Research, 2019). The study was run by a pet food company and covers one breed prone to gum disease.
Treatment is the stage 1 cleaning plus cleaning under the gum. If a pocket is still deeper than 5 mm once it's clean, your vet may place an antimicrobial in it (AAHA, 2019). Attachment that has gone doesn't grow back on its own, but a treated stage 2 tooth can be kept stable as long as plaque is kept off it. Our article on what happens at a dog dental cleaning walks through each step.
Stage 3, moderate periodontitis
Stage 3 means a quarter to a half of the support has gone. The pockets are deeper, and on teeth with more than one root the probe may pass more than halfway under the crown. You might see the gum pulled back with part of a root showing, often with tartar. Some stage 3 teeth look ordinary from the outside.
The AAHA guidelines say treatment to save a stage 3 tooth, such as root planing, antimicrobials in the pockets or gum surgery, will only work if the owner commits to home care every day. If that can't happen, extraction is the recommended choice. Plaque starts sticking to a cleaned tooth again within 24 hours (Gawor and colleagues, 2025), and no home method reaches under the gum line, so a saved tooth depends on the gum above it staying clean.
Lost bone doesn't grow back on its own. In a few selected teeth a veterinary dentist can try regenerative surgery, which AAHA lists at this stage, and it needs the same daily home care.
Stage 4, advanced periodontitis
At stage 4 more than half of the tooth's support has gone. On a back tooth a probe may pass right through between the roots, and the tooth may move when touched. You might notice a loose tooth, pus at the gum or chewing on one side. Sometimes there's nothing to see, because dogs keep eating through mouth pain.
When pockets or gum loss pass half the root, the AAHA guidelines say extraction is indicated. The alternative is surgery to reshape or rebuild the bone, followed by daily home care, and AAHA calls the outlook at this stage guarded.
For the other reasons a vet takes a tooth out, from a broken crown to a baby tooth that never let go, see our guide to dog tooth extraction.
What home care can do at each stage
Brushing removes plaque, not tartar, and the AAHA guidelines say it has to be daily to help.
- At stage 0 and 1, daily brushing with a dog toothpaste keeps plaque from hardening and lets inflamed gum settle. If there's tartar already, the gum won't settle until a vet has cleaned it off.
- At stage 2, home care keeps a cleaned tooth from losing more support. It can't reach the bottom of a pocket, so the checks under anesthesia still matter.
- At stage 3, daily home care is the condition for keeping the tooth at all.
- At stage 4, it protects the teeth that are left after extractions.
Don't start brushing a mouth that's already sore. AAHA notes that brushing inflamed gums hurts and puts dogs off the brush, so get the mouth treated first. After extractions or gum surgery, wait until your vet says the gum has healed. AAHA recommends a recheck 10 to 14 days after any dental, which is a good time to ask.
Some human toothpastes contain xylitol, which is poisonous to dogs, so keep to a dog toothpaste. For a dog that won't take a brush, the Veterinary Oral Health Council (VOHC) seal means the maker's trials showed slower plaque or tartar build-up, and our guide to cleaning your dog's teeth at home ranks the methods by evidence. None of them changes the stage of a tooth that has already lost bone.
When to see a vet
- The same day for a swollen face, bleeding from the mouth that won't stop, or a dog that has stopped eating
- Within a few days for a loose tooth, pus at the gum line, or chewing on one side and dropping food
- Within a week or two for red or receding gums, a root showing, or bad breath that doesn't clear
- At every routine check, even if your dog seems fine, because the look of the gums often gets the stage wrong. AAHA suggests an awake mouth check every 6 months
Questions owners ask
How long can a dog live with stage 4 periodontal disease?
No study gives a life expectancy for dogs with stage 4 teeth. Stage 4 teeth are painful, and treatment makes your dog's years more comfortable.
Can stage 3 periodontal disease be reversed?
Not fully. Bone and ligament that have gone don't come back by themselves. Treatment can stop the tooth getting worse, and in selected teeth regenerative surgery can win back some attachment. Both depend on daily home care afterward.
How fast does periodontal disease progress in dogs?
It varies by dog, breed and tooth, so nobody can give you a timetable. In the Yorkshire terrier colony above, the share of teeth with periodontitis rose from about a quarter to about half in ten months, though nearly all stayed at stage 2.
Is my dog in pain with periodontal disease?
Inflamed gums are tender, and teeth with deep pockets, infection or movement hurt more. Dogs rarely show it by crying or skipping meals. Watch for chewing on one side, dropping food, pawing at the mouth, or a dog that has gone off its hard chews.
References
- American Veterinary Dental College. Nomenclature (periodontal disease stages, furcation, mobility), avdc.org/avdc-nomenclature.
- Bauer AE, Stella J, Lemmons M, Croney CC. Evaluating the validity and reliability of a visual dental scale for detection of periodontal disease (PD) in non-anesthetized dogs (Canis familiaris). PLoS One. 2018;13(9), e0203930. doi:10.1371/journal.pone.0203930.
- Bellows J, Berg ML, Dennis S, et al. 2019 AAHA dental care guidelines for dogs and cats. J Am Anim Hosp Assoc. 2019;55(2), 49-69. doi:10.5326/JAAHA-MS-6933.
- Gawor J, Jank M, Harvey CE, Nicolas CS. Effectiveness of dental homecare protocols in unscaled dogs. J Vet Dent. 2025;42(3), 176-181. doi:10.1177/08987564241292769.
- Marshall MD, Wallis CV, Milella L, Colyer A, Tweedie AD, Harris S. A longitudinal assessment of periodontal disease in 52 miniature schnauzers. BMC Vet Res. 2014;10, 166. doi:10.1186/1746-6148-10-166.
- Merck Veterinary Manual. Xylitol toxicosis in dogs. Updated June 2025. merckvetmanual.com.
- Queck KE, Chapman A, Herzog LJ, et al. Oral-fluid thiol-detection test identifies underlying active periodontal disease not detected by the visual awake examination. J Am Anim Hosp Assoc. 2018;54(3), 132-137. doi:10.5326/JAAHA-MS-6607.
- Wallis C, Pesci I, Colyer A, et al. A longitudinal assessment of periodontal disease in Yorkshire terriers. BMC Vet Res. 2019;15, 207. doi:10.1186/s12917-019-1923-8.
- Veterinary Oral Health Council. vohc.org.