Canine periodontal disease staging, diagnosis and treatment

What periodontal disease is and which dogs get it

Merck describes periodontal disease as infection and inflammation of the periodontium, the tissues that surround and support the teeth [1]. It begins with plaque, a bacterial biofilm on the tooth surface, and the host's inflammatory response to it. Untreated gingivitis can progress to periodontitis, which involves the deeper structures [1]. The AVDC defines periodontitis as inflammation of the periodontal ligament and alveolar bone [2]. Merck notes that as plaque thickens and oxygen is depleted, the bacterial population shifts toward gram-negative anaerobic rods. It also notes that periodontitis is driven by the host's response to plaque below the gumline [1].

Calculus (tartar) is mineralized plaque. Merck states that its contribution to periodontal disease is "minor," even though it makes teeth look unhealthy [1]. Niemiec, writing in Today's Veterinary Practice, calls calculus "essentially nonpathogenic" on its own [4].

On frequency, Merck cites an older textbook figure that up to 80% of dogs have some level of periodontal disease by age 2 [1]. Merck lists the following risk factors [1]:

• toy breeds
• immunosuppression, such as diabetes mellitus or hyperadrenocorticism
• poor nutrition
• malocclusion

The 2021 JSAP cohort study by O'Neill and colleagues used VetCompass records from 784 UK clinics [3]. Compared with crossbreds, these breeds had the highest adjusted odds [3]:

• Toy Poodles (aOR 3.97)
• King Charles Spaniels (2.63)
• Greyhounds (2.58)
• Cavalier King Charles Spaniels (2.39)

The study also reported these associations [3]:

• Dogs under 10 kg had 3.07 times the adjusted odds of dogs weighing 30 to under 40 kg.
• Brachycephalic types had 1.25 times the odds of mesocephalic types.
• Odds rose steadily with age.
• German Shepherd Dogs, French Bulldogs, Staffordshire Bull Terriers, and Labrador Retrievers had reduced odds.

The authors note several limitations [3]. Cases were classified only as yes or no, without severity. Records often did not distinguish gingivitis from periodontitis. The authors also say true cases were likely missed in primary care, so prevalence may be underestimated.

Clinical signs

Merck lists the following signs [1]:

• halitosis
• plaque and calculus
• red, swollen, and bleeding gums
• gingival recession
• periodontal pocketing
• bone loss
• furcation exposure
• mobile teeth
• eventual tooth loss

Niemiec writes that increased bleeding on probing or brushing appears before gingival color change. He also says color change is unreliable in dogs with dark pigmented gingiva [4]. Merck notes systemic associations, including an increased risk of chronic azotemic kidney disease. Two of the references Merck cites for this are studies in cats [1]. The JSAP authors cite reported associations with kidney, heart, and liver disease [3].

Staging and classification

The AVDC uses "stage" for the extent of lesions in a disease likely to progress, and periodontal disease is its example [2]. The table below follows the AVDC and Merck definitions [1][2].

Stage	AVDC/Merck criteria
PD0	Clinically normal; no evident gingivitis or periodontitis
PD1	Gingivitis only, no attachment loss, normal alveolar margin
PD2	Early periodontitis; under 25% attachment loss, or at most stage 1 furcation involvement
PD3	Moderate periodontitis; 25% to 50% attachment loss, or stage 2 furcation involvement
PD4	Advanced periodontitis; over 50% attachment loss, or stage 3 furcation involvement

Attachment loss is measured in one of two ways [2]. The first is probing. The second is radiographic: the distance from the cementoenamel junction to the alveolar margin, relative to root length.

Furcation is the area where the roots of a multirooted tooth meet. The AVDC grades furcation involvement as follows [2]:

• F1: the probe extends "less than half way under the crown."
• F2: the probe extends more than halfway but not through.
• F3: the probe passes "through and through."

Merck's wording for F2 is "approximately halfway" [1].

The AVDC mobility index has four stages [2]:

• M0: physiologic movement up to 0.2 mm.
• M1: over 0.2 mm up to 0.5 mm.
• M2: over 0.5 mm up to 1.0 mm.
• M3: over 1.0 mm, or any axial movement.

Merck separately describes whole-mouth calculus and gingivitis indices graded 0 to 3. On the gingivitis index, grade 2 includes bleeding on probing and grade 3 includes spontaneous bleeding [1].

Diagnosis and testing pitfalls

Merck describes three steps: a conscious oral exam, an anesthetized oral exam, and intraoral dental radiography [1]. It cautions that conscious findings are limited, because only external tooth surfaces can be seen and the patient has to cooperate [1]. Under anesthesia, each tooth is probed at six sites, and furcation and mobility are assessed and recorded on a dental chart [1]. Merck notes that the 2019 AAHA Dental Care Guidelines "strongly recommends full-mouth intraoral dental radiography in all dental patients" [1].

Niemiec describes several common errors [4]:

• Judging disease by the amount of calculus. He advises using gingival inflammation instead, while noting that even this can underestimate severity.
• Relying on visual exam alone. He describes a 15 mm pocket on a mandibular first molar beneath gingiva that looked relatively normal.
• Using radiographs in place of probing. He writes that bone loss does not show on radiographs until 30% to 50% of mineralization is lost. He adds that F1 furcation exposure is not radiographically evident, and that overlapping structures and angulation errors can hide or distort lesions.
• Probing alone in tight spaces. Calculus ledges and tight contacts can block the probe, so he pairs probing with radiography.

At minimum, Niemiec recommends radiographing any pocket greater than 3 mm in dogs. He also suggests full-mouth radiographs for all dogs under 15 lb [4]. He describes in-room thiol test strips as a way to show periodontal infection in patients without obvious inflammation or calculus [4]. The JSAP authors cite a study in which only 82% of dogs with active disease on anesthetized exam showed inflammation on conscious visual exam [3].

Treatment by severity

Merck states that treatment "depends on the severity of attachment loss" [1].

For gingivitis (PD1), Merck says removing plaque through scaling and polishing under general anesthesia can return the gingiva to a healthy state [1]. If gingivitis persists, Merck advises looking for residual subgingival deposits or predisposing factors. It also advises considering less common causes such as uremic stomatitis or autoimmune disease [1].

For periodontitis (PD2 to PD4), Merck describes root scaling, root planing, and gingival curettage. Shallow pockets are treated closed, without a flap, while pockets over 5 to 6 mm need an open flap procedure [1]. Per Merck, a perioceutic "may be helpful" [1]. This is a local antimicrobial, such as doxycycline, placed into a cleaned pocket. The cited sources give no dose. Bone grafts and barrier membranes for guided tissue regeneration can be used to address lost bone [1].

Niemiec states that teeth with pockets over 6 mm or with stage 2 or 3 furcation exposure cannot be cleaned effectively by closed root planing. These teeth require extraction or referral for flap surgery, even if they are not yet mobile [4]. Merck describes two further indications for extraction [1]:

• Teeth that are mobile from attachment loss should be extracted.
• A palatal pocket on a maxillary canine that has formed an oronasal fistula requires extraction and fistula repair.

Merck adds that periodontitis reaching the root apex or a furcation canal can cause secondary endodontic disease [1].

Merck defines professional dental cleaning as scaling and polishing under general anesthesia. The AVDC's definition includes removal of both supragingival and subgingival plaque and calculus [1][2]. Merck warns that cleaning an awake animal may lead owners to believe the disease has been treated while it continues below the gumline [1]. Niemiec describes dogs that had regular anesthesia-free cleanings and had clean crowns but deep pockets [4].

Prognosis, prevention and client communication

Merck states that periodontitis is "not as easily reversible as gingivitis" and that disease will recur "without drastic changes in home oral hygiene" [1]. It also notes that dogs can function without teeth and may have an improved quality of life after diseased teeth are extracted [1].

For home care, Merck states that daily or at least every other day toothbrushing appears to be the most effective way to improve and maintain periodontal health [1]. It notes that plaque left for more than 2 days mineralizes into calculus that brushing cannot remove [1]. Merck makes three further points on chews and diet [1]:

• Hard chews such as bones and hooves can crack teeth and should be avoided.
• The belief that dry kibble cleans teeth "does not necessarily always hold true."
• The Veterinary Oral Health Council lists products that meet plaque and calculus standards.

Our read for client conversations is that the sources support three points:

• Visible tartar is a poor guide to severity.
• Staging needs anesthesia.
• The treatment plan may change once probing and radiographs are done.

Niemiec recommends discussing possible treatments and costs before the procedure [4].