Periodontal Disease and Oral Hygiene

2. Periodontal Disease and Oral Hygiene

Unlike in humans, dental caries is very rare in dogs. A study of 435 dogs presented at a practice specialized in veterinary dentistry reported that only 23 dogs (5.3%) presented with caries (Hale, 1998). The most common oral malady in dogs is periodontal disease, and most of this chapter is devoted to it.

Periodontal Disease

Periodontal disease is the result of a fight at tissue level (periodontium = gingiva, alveolar bone, periodontal ligament and cementum) between bacteria that accumulate on the dental crowns (bacterial dental plaque) and the individual's defense system (Figure 5).

Figure 5. Periodontal disease.

Epidemiology

Periodontal disease affects every dog in the course of its life, although prevalence varies depending on the breed and the individual. The accumulation of bacterial dental plaque on the dental crowns along the gingiva leads to an inflammatory reaction in this gingiva known as gingivitis. Traditionally, the external surfaces (vestibular) of the teeth are more severely affected than the internal surfaces (palatines or lingual), and the maxillary teeth are more affected than the mandibular teeth (Isogai et al., 1989; Rosenberg et al., 1966; Harvey et al., 1994) (Figure 6).

Figure 6. Comparison of dental plaque on the teeth of small dogs. (Hennet et al., 2004).

Influence of the Size of the Dog

Small dogs (weighing less than 8 kg) suffer earlier and more severely, particularly on the incisors and the internal surfaces of the teeth (Harvey et al., 1994). The smaller the dog, the greater the volume of the teeth in the jaw. As a result, in the event of periodontitis, the gradual destruction of the alveolar bone along the root may threaten the very solidity of the jaw. It has been shown that the ratio [height of the mandible / height of the first molar] in dogs decreases significantly in conjunction with the size of the dog (Gioso et al., 2001) (Figure 7).

Figure 7. Relationship between the dog’s weight and the ratio "height of the mandible (D) / height of the mandibular carnassial (C)". (Gioso et al., 2001).

The loss of a few millimeters of bone in a Yorkshire Terrier has greater consequences than it has for a large dog. The jaw may become so fragile that fractures occur. In Yorkshire Terriers, oral disease represents the primary reason for veterinarian consultation among all age groups (Veterinary Medical Data Base, 1979-1999).

Influence of the Individual

The transition from gingivitis to periodontitis is a phenomenon specific to each individual. It depends on limiting the development of infection through oral hygiene and/or the individual's local immune system.

Influence of Age

A study has shown that 80% of dogs older than six years of age presented with moderate to severe periodontitis characterized by destruction of bone (Hamp et al., 1984). The supragingival dental plaque is gradually mineralized into calculus by salivary secretions. The calculus may become visible a few weeks after the dental plaque starts to accumulate. In a study of young Beagles, by the age of 26 months, 95% of the dogs presented with a very large accumulation of calculus as well as serious gingival inflammation accompanied by periodontitis (Rosenberg et al., 1966). Periodontal disease is naturally aggravated with age. There is a significant statistical correlation between age and the gingival index (intensity of the inflammation), the calculus index (quantity of calculus), the tooth mobility index and the furcation index (importance of the interradicular bone resorption) (Harvey et al., 1994).

Influence of Sex

No sexual predisposition has been shown in the canine species.

The Causes of the Disease

Bacterial dental plaque is a natural bacterial film (biofilm) that develops on the surface of the teeth (Overman, 2000) (Figure 8).

Gingivitis in dogs. Accumulation of dental plaque with gradual formation of calculus, responsible for inflammation of the gingiva without destruction of deeper-lying tissue. (© Ph. Hennet).

Figure 8. Healthy tooth and gum. The biofilm constituting the dental plaque is made up of numerous bacteria inserted in a glycoprotein matrix that forms a kind of natural glue. The bacteria communicate with each other by chemical signals that trigger the production of proteins and potentially harmful enzymes.

There are more than 350 recorded strains of bacteria in the oral cavity. Periodontal inflammation of the gingiva without destruction of deeper-lying tissue. disease is accordingly not caused by a single strain. These bacteria first accumulate in large numbers on the visible surface of the teeth (supragingival dental plaque), before spreading under the gingiva (subgingival plaque). A milligram of dental plaque contains around 10 million bacteria (Loesche, 1988). In contact with the gingiva, these bacteria naturally provoke an inflammatory reaction, known as gingivitis.

The bacteria that spread under the gingiva may also gradually provoke more deep-lying lesions (destruction of the gingiva, periodontal ligament lesions, lesion of the alveolar bone that supports the tooth). These deep lesions loosen the tooth, which becomes more and more mobile. This characterizes the periodontitis phase. The normal attachment of the periodontium to the tooth is destroyed and migrates to the extremity of the root (= loss of attachment), resulting in the creation of a periodontal pocket. The depth of this pocket depends on the concomitant rate of gingival recession.

Calculus is formed by the gradual mineralization of the dental plaque caused by mineral salts (especially calcium) provided by the saliva for supragingival plaque, or by the gingival fluid in which the gingival crevice is immersed, for subgingival plaque. Calculus is not responsible for periodontal disease, but on a rough surface it is an ideal medium for bacterial dental plaque. In the event of chronic periodontal disease the calculus is indivisible from the bacterial dental plaque. It must be eliminated to enable the eradication of plaque. Limiting the formation of calculus while curbing the formation of bacterial dental plaque is one of the objectives of oral hygiene.

Certain factors (reduced masticatory activity, dental malocclusion, persistence of deciduous teeth, absence of oral hygiene) can advance the accumulation of dental plaque. Other factors that affect the individual's capacity to develop a normal defense reaction include: systemic diseases (diabetes mellitus, kidney failure, liver failure) and innate or acquired immunodeficiency. The individual's capacity to develop an appropriate defense reaction is an innate factor. In general, the dog presents increased dental plaque and calculus accumulation and more serious gingivitis when it is nourished with soft, sticky food compared with firm, fibrous food (Egelberg, 1965; Kaplan et al., 1978).

This apparent advantage in favor of firm, fibrous food applies only when the food is given in the form of large pieces, which encourages the use of the teeth.

Oral Hygiene

While not every individual that presents gingivitis automatically develops periodontitis, gingivitis is the essential preliminary stage in the development of periodontitis. The very principle of oral hygiene is therefore based on the control of supragingival dental plaque. A study of Beagles suffering from light to moderate periodontitis has shown that professional periodontal treatment (scaling, subgingival debridement and polishing), followed by daily brushing, helps reduce the initial loss of attachment and maintains this gain over a three-year period. Additional periodontal treatment every six months over this period does not improve the periodontal condition: neither does this same treatment every six months in the absence of daily brushing which helps prevent the deepening of the pockets and the loss of attachment (Morrison et al., 1979).

Periodontitis in the dog. Destruction of the tissue that attaches to the tooth. In the absence of treatment, this will ultimately result in tooth loss (©Ph. Hennet).

Oral hygiene can be split into primary hygiene (preventive measures on healthy gingivae before periodontal disease develops) and secondary hygiene (prevention of recurrence, after professional periodontal treatment of a pre-existing periodontal disease). In all cases, primary prevention is always desirable, because it occurs earlier and thefore is more effective. The puppy must be educated from a very early age. While oral hygiene applies to all dogs and all breeds, the main targets are small and miniature dogs.

Aspect of the teeth of the same dog from the right (A) and the left (B). At right all teeth are presented and the deposits of dental plaque and calculus are very low. At right, the maxillary carnassial is absent, which means that there is no mechanical effect with the mandibular carnassial, resulting in major accumulation of dental plaque and calculus. (© P. Hennet).

Brushing

Tooth brushing is the gold standard in terms of controlling supragingival dental plaque.

In humans, an efficacy of the order of 70% inhibition of dental plaque can be asserted, at least for the most accessible vestibular surfaces (Mankodi et al., 1998; Van der Weijden et al., 1998). Studies of Beagles have shown that brushing at least three times a week helps maintain healthy gingivae, while brushing once a week does not (Tromp et al., 1986a). In the presence of gingivitis, only daily brushing will re-establish healthy gingivae (Tromp et al., 1986b). The only clinical study published on tooth brushing in dogs shows that, during a 13-month period, 49 of 51 owners (96%) recall having received brushing instructions and 34 of 51 owners (67%) recall having been shown how to brush teeth; 15 of 51 owners (2%) always brush the dog's teeth several times a week and 12 of 51 owners (24%) do so every day or every second day (Miller & Harvey, 1994).

While being a reference in oral hygiene, brushing is not an easy task for owners to presented and the deposits of dental plaque and accomplish. Brushing can be complemented with the use of active chemical substances, of which chlorhexidine is still the most effective. In a study of Beagles in which the dogs' teeth and gums were massaged every day with a dental gel containing chlorhexidine and other ingredients, dental plaque on the vestibular surfaces was reduced by 42 - 49% (Hennet, 2002). Whether these products are applied through brushing or massage, they do necessitate the intervention of the owner and the cooperation of the animal. These limitations have naturally led to the development of other oral hygiene means that do not require the owner's direct intervention. These indirect means comprise collagen-based chewing bones that can or cannot be eaten and specific dental foods.