Periodontal disease

What it is

Periodontal disease is inflammation of the periodontium, the tissues that hold the tooth in place: the gingiva, the periodontal ligament, the root cementum and the alveolar bone. The cause is dental plaque, a bacterial biofilm that forms on the tooth within hours of cleaning. Plaque that mineralises forms calculus (tartar), whose rough surface retains more plaque, but it is the bacteria, not the calculus itself, that cause the inflammation.

• Gingivitis: inflammation limited to the gingiva, with redness, oedema and bleeding. It is reversible if the plaque is removed.
• Periodontitis: when plaque extends below the gumline, the flora shifts towards anaerobic gram-negative bacteria and the animal's own inflammatory response destroys the periodontal ligament and alveolar bone. This causes attachment loss, with periodontal pockets, gingival recession, exposure of the furcation (the area between the roots of multi-rooted teeth), mobility and finally tooth loss. This destruction is irreversible; treatment can only slow it.

Under the American Veterinary Dental College (AVDC) classification, each tooth is staged as PD0 (normal), PD1 (gingivitis only, no attachment loss), PD2 (early periodontitis, with less than 25% attachment loss), PD3 (moderate periodontitis, 25 to 50%) and PD4 (advanced periodontitis, more than 50%); in multi-rooted teeth the degree of furcation exposure also counts.

Who it affects

Most adult dogs to some degree, and its frequency increases with age. Small and toy breeds are the most affected: their teeth are large in proportion to the jaws, with little bone around the roots, and more crowded. Brachycephalic breeds are also predisposed, because of crowding and rotation of the teeth, as are some specific breeds such as the Greyhound. Soft diets, lack of oral hygiene and malocclusion contribute.

Anatomy involved

• Mandible: the lower teeth sit in the alveoli of the incisive part and body of the mandible. Periodontitis resorbs the alveolar bone around the roots, with horizontal or vertical bone loss and furcation involvement. In small-breed dogs the roots of the mandibular first molar occupy almost the full height of the mandibular body; when periodontitis destroys the surrounding bone, the mandible can break with minimal trauma or during an extraction (pathological fracture). Infection can spread to the bone (osteomyelitis).
• Skull: the upper teeth sit in the maxilla and incisive bone. The roots of the upper canine are separated from the nasal cavity by a very thin plate of bone; when it is destroyed on the palatal side an oronasal fistula forms, with chronic rhinitis, sneezing and nasal discharge on the same side. The roots of the upper fourth premolar and molars lie next to the orbit, so their infection can cause facial swelling below the eye, retrobulbar abscesses and other ocular complications.

Clinical signs

Many animals show no obvious signs; oral pain often goes unnoticed by the owner. The most common signs are halitosis, visible plaque and calculus, red gingiva that bleeds easily, gingival recession, mobile or missing teeth, chewing on one side, dropping food, reluctance to play with hard toys, blood in the saliva, facial swelling or draining tracts below the eye and, with an oronasal fistula, sneezing and nasal discharge.

Diagnosis

• Conscious oral examination: detects gingivitis, calculus and obvious cases, but underestimates the disease, because much of the lesion lies below the gumline.
• Examination under general anaesthesia: every surface of every tooth is probed with a periodontal probe to measure pockets and attachment loss, furcation and mobility are assessed and everything is recorded on a dental chart.
• Full-mouth intraoral dental radiography: essential to see alveolar bone loss, furcation involvement, periapical lesions and fractures, and to decide which teeth are kept and which are extracted.

Treatment and prevention

Professional treatment is always performed under general anaesthesia with tracheal intubation, which protects the airway and allows work below the gumline: supragingival and subgingival scaling, root planing, polishing, irrigation and, depending on the stage, periodontal surgery or extraction of teeth that cannot be saved, with analgesia and local anaesthetic blocks. Antibiotics are not routinely needed.

Anaesthesia-free dental cleaning only removes visible calculus from the crown, does not treat the disease below the gumline, prevents examination and radiographs and gives a false sense of a healthy mouth; guidelines do not recommend it. The AAHA guidelines describe all dental treatment under general anaesthesia, and the WSAVA guidelines consider anaesthesia-free cleaning ineffective at best and harmful at worst.

Prevention relies on home oral hygiene: daily toothbrushing with a pet toothbrush and toothpaste is the most effective method. Diets, chews or water additives carrying the Veterinary Oral Health Council (VOHC) seal, which indicates that the product has been shown in trials to slow plaque or calculus accumulation, can be used as adjuncts. Oral check-ups are recommended at least once a year, more often in predisposed breeds.

Several large cohort studies associate severe periodontal disease with a higher risk of chronic kidney disease. These are observational studies: they show an association, they do not prove that periodontal disease causes kidney disease or that treating it prevents it.

In the cat

Periodontal disease is also very common in cats and, as in dogs, increases with age. The mechanism is the same, but there are particular features:

• Gingival recession and horizontal bone loss are common, and the canines may show alveolar bone expansion on the buccal side that makes them look longer.
• The gingiva and the bone supporting it are thin, so furcation involvement and mobility appear early, especially in the premolars and molars of the mandible and maxilla. Advanced disease of the upper canines can also open an oronasal fistula.
• It often coexists with tooth resorption, which has its own entry in the atlas ("Feline tooth resorption"), and must be distinguished from feline chronic gingivostomatitis, a much more extensive inflammation of the oral mucosa.
• Cats hide oral pain very well: advanced disease can be present in a cat that is still eating.

Diagnosis and treatment are the same as in dogs, under general anaesthesia and with full-mouth radiographs; extraction is often the most reasonable option for teeth with advanced disease. Daily brushing is effective, but many cats tolerate it less well than dogs, and there are diets and products with the VOHC seal for cats.

Key studies

• WSAVA dental guidelines (Niemiec et al., 2026): global consensus that defines gold-standard treatment and minimum standards of care in veterinary dentistry, including anaesthesia, pain management and home oral care. It considers untreated oral disease a significant animal welfare problem and describes anaesthesia-free dentistry as ineffective at best and harmful at worst.
• O'Neill et al. (2021), cohort study of a random sample of 22,333 dogs under primary veterinary care in the UK (VetCompass). The one-year period prevalence of diagnosed periodontal disease was 12.52%. The breeds at highest risk compared with crossbreds were the Toy Poodle (odds ratio 3.97), King Charles Spaniel (2.63), Greyhound (2.58) and Cavalier King Charles Spaniel (2.39); brachycephalic breeds had 1.25 times the odds of mesocephalic breeds, and risk decreased as adult body weight increased. It is based on diagnoses recorded in practice, so it probably underestimates the true prevalence.
• Harvey et al. (2015), randomised, controlled, blinded trial in laboratory beagles comparing daily, every-other-day, weekly and every-other-week brushing with no brushing over 28 days. The more frequent the brushing, the less plaque and calculus accumulated and the more gingivitis improved; brushing daily or every other day was significantly better than weekly or every other week. It is a short study, in laboratory dogs, and the abstract does not give the number of animals.
• Glickman et al. (2011), retrospective cohort of 164,706 dogs with periodontal disease and age-matched dogs without it, from a national primary-care practice in the United States. The risk of azotaemic chronic kidney disease increased with the severity of periodontal disease: hazard ratio 1.8 in stage 1, 2.0 in stage 2 and 2.7 in stages 3–4, after adjustment for age, sex, breed, weight and other factors. It is an observational study based on medical records; it does not prove causation.
• O'Neill et al. (2023), study of a random sample of 18,249 cats under primary veterinary care in the UK (VetCompass). The one-year period prevalence of diagnosed periodontal disease was 15.2%, the highest of any specific diagnosis. The median age of affected cats was 9.47 years versus 4.94 in unaffected cats, and age was the strongest risk factor. Cats with periodontal disease had 1.79 times the odds of having at least one other disorder, an association that does not prove causation.
• Trevejo et al. (2018), retrospective cohort of 169,242 cats seen at 829 hospitals in the United States: 56,414 with periodontal disease and 112,828 without, matched by age. Periodontal disease was associated with a higher risk of azotaemic chronic kidney disease, highest in stages 3 and 4. It is an observational study based on medical records; the association may be partly due to unmeasured factors.