The pathophysiology of periodontal disease
By Kathy Istace, RVT, VTS (Dentistry)
Periodontal disease is the most common infectious disease in both humans and pets. It is the most commonly seen oral problem, suggesting that our current preventive measures are either not widely practiced, or are not widely successful. Periodontal disease can be briefly described as inflammation leading to recession of the periodontium(tissues surrounding the teeth), however, the process that causes this disease is complex.
Development of periodontal disease
After a meal, naturally-occurring microorganisms in the mouth mix with salivary glycoproteins, polysaccharides from ingested food, sloughed epithelial cells, and white blood cells. This mixture forms plaque, a soft, sticky biofilm that adheres to the tooth’s surface. This soft plaque is initially confined to the tooth’s crown, and contains predominantly Gram-positive, non-motile, aerobic cocci. When these cocci contact the gingiva, they stimulate an inflammatory response. Neutrophils engulf the bacteria, and burst when full, releasing toxins and enzymes that irritate the patient’s periodontal tissues, causing inflammation of the gingival margin. This inflammation causes the attached gingiva to loosen from the tooth, creating a space between the tooth and the gingiva known as a periodontal pocket. The bacteria also secrete substances that improve the biofilm’s adhesion to the tooth and protect the bacteria from antimicrobial agents – making the bacteria within this biofilm up to 1500 times more resistant to antiseptics and antibiotics than the same bacteria would be by itself. Oxygen is no longer able to reach the deepest layers of this thick matrix, so the bacterial population begins to shift, with Gram-negative, anaerobic, mobile rods and filamentous organisms taking over. These anaerobes are more virulent than the surface-dwelling aerobes, producing endotoxins, which, along with the patient’s own defense mechanisms, lead to soft tissue loss (or sometimes, overgrowth of the gingival tissue called gingival hyperplasia), progressing to bone loss, and eventually, tooth loss. This loss of periodontal support is known as attachment loss.
If plaque is not brushed off, within 2-3 days calcium from food and saliva begin to mineralize it into a hard substance called calculus or tartar. Calculus doesn’t cause periodontal disease, but it has a rough, porous surface that makes a great home for disease-causing bacteria.
The stages of periodontal disease
Periodontal Disease Index is scored by the amount of attachment loss. It is primarily determined by measuring periodontal pocket depths and radiographic assessment of bone loss. There may be (and usually are) teeth with different periodontal indices within the same mouth.
PD0: Normal
- Attachment loss is 0%
- No inflammation of the gingiva, it is pink, smooth, and lies flat against the teeth
- No treatment required, dental homecare should be initiated to maintain oral health
PD1: Gingivitis
- Attachment loss is 0%
- Gingivitis only
- May be a slight increase in sulcus depth because of gingival swelling (pseudopocket) though no attachment loss has yet occurred
- Bacteria are Gram-positive, aerobic, non-motile cocci
- This is the only stage of periodontal disease that is reversible!
- Treatment: dental COHAT (Comprehensive Oral Health Assessment and Treatment) including teeth cleaning under general anesthesia to remove all biofilm and reverse inflammation, homecare
PD2: Early periodontitis
- Attachment loss is < 25%
- Bacteria in subgingival regions are Gram-negative, anaerobic, motile rods
- Pocket depth increases due to attachment loss
- Crestal bone (bone at the level of the cemento-enamel junction) starts to deteriorate
- Treatment: dental COHAT and closed root planing. Perioceutics (antibiotic gels) can be placed within the periodontal pockets to kill bacteria and relieve inflammation. Homecare
PD3: Moderate periodontitis
- Attachment loss is 25-50%
- Bacterial population is almost entirely anaerobic
- Alveolar bone starts to deteriorate, leading to vertical bone loss and horizontal bone loss
- Tooth roots may be exposed, possible furcation exposure
- Alveolitis (inflammation of the tooth socket) or osteomyelitis (bone infection) may be present
- Treatment: frequent dental COHATs and periodontal therapyincluding open root planing. Homecare
PD4: Severe periodontitis
- Attachment loss is > 50%
- Bacterial population similar to PD3
- Tooth roots and root furcations are exposed
- Teeth may be mobile, some only held in position by calculus or granulation tissue
- Teeth with more than 50% attachment loss may not be able to be salvaged
- Treatment: assess whether each tooth can or should be saved
Without intervention, periodontal disease will progress until the teeth exfoliate. At this point, since there is no longer any tooth surface for bacteria to cling to, the periodontal tissues can heal. Until such time, the patient suffers with chronic infection and oral pain. Bacterial infection in the mouth can cause disease elsewhere in the body, such as endocarditis. Each time an animal with periodontal disease chews, tiny abrasions occur in the fragile, infected periodontal tissues. Capillaries in these abrasions rupture, allowing bacteria to enter the bloodstream and settle in the heart valves, kidneys, or liver. This is especially dangerous in patients whose health is already comprised, such as diabetics, the immunosuppressed, or those in poor body condition.
Contributors to periodontal disease
There are several factors that can predispose a pet to periodontal disease, or worsen existing periodontal disease.
- Crowded teeth
- Retained deciduous (baby) teeth
- Malocclusions
- Supernumerary teeth
- Enamel hypocalcification
- Diet: feeding solely soft diets has been correlated with a higher incidence of periodontal disease vs. feeding mixed soft and dry diets, or strictly dry kibble
- Malnutrition, physical or psychological Stress
- Genetics
- Other factors: chewing habits, mouth architecture, saliva flow, general health status
Clinical signs of periodontal disease
- Halitosis(the most common reason pet owners present their animals for oral examination)
- Red, inflamed gingiva (common, less often noted by owners)
- Increased drooling, or blood in the saliva (uncommon)
- Pawing at mouth (rare)
- Difficulty eating (rare, though some animals will prefer soft food)
