Role of Food in Oral Hygiene

3. Role of Food in Oral Hygiene

Influence of the Food's Composition

When the composition of a food is changed but not its consistency, no significant influence is observed on the development of periodontal disease. Protein deficiency does not appear to have any consequence (Ruben et al., 1962). A protein-lipid (P-L) diet (50 - 50% in dry weight) or the addition of carbohydrates (C) (60% C, 20% P, 20% L) does not lead to an aggravation of periodontal disease (Carlsson & Egelberg, 1965; Egelberg, 1965). Osteopenia of alveolar bone induced by secondary hyperparathyroidism with a nutritional cause (Ca/P = 0.1) does not appear to influence the initiation and advancement of periodontal disease (Svanberg et al., 1973).

The active agents against dental plaque or calculus can be incorporated into a kibble or a chewing bar. They are then released in the oral environment during mastication. Anti-calculus agents such as polyphosphates were studied first (Stookey et al., 1993). These are phosphate polymers (pyrophosphate, polyphosphate, hexametaphosphate), some of which present sequestering properties with bivalent cations like calcium (Figure 9).

The chelation of salivary calcium is responsible for inhibiting the formation of calculus. To facilitate the release and the contact with salivary calcium, the polyphosphates must be incorporated in the kibble coating (Stookey et al., 1993).

Other compounds (polyphenols, essential oils, metallic ion salts, etc.) that have exhibited in vitro or in vivo activity on the formation of dental plaque may also be incorporated. Studies are needed to evaluate their activity in these conditions and to determine the best way of optimizing the release of these substances in the oral cavity (in the external coating or in the kibble proper).

Figure 9. Mechanism of salivary calcium chelation by sodium polyphosphate.

Influence of the Physical Presentation of the Food

While it appears logical that a soft food or food in very small pieces would not help the function of the teeth and manducation in canids, interest in the role played by the food is a relatively recent phenomenon.

Studies conducted by physiologists have shown that gastrectomized dogs fed with a soft food developed more calculus (Ivy et al., 1931). In a study in which one group of dogs were fed with slices of entire beef, the esophagus, the muscles and a mineral and vitamin supplement, and another group was fed with the same food minced, the dogs in the second group presented with greater accumulation of dental plaque than the dogs in the first group (Egelberg, 1965). Many other studies have confirmed this (Krasse & Brill, 1960; Kaplan et al., 1978). In addition to the absence of mechanical action, a soft food can provoke a reduction in the flow of saliva, a reduction in enzyme secretions and functional atrophy (Sreebny, 1972).

It cannot simply be concluded however that a food in kibble form or a hard food is generally more effective than a soft food. In Egelberg's study (1965) the main factor is the fibrous character of the food rather than its hardness. A multicenter study on 1350 dogs in North America has shown that there is no significant difference between dogs fed exclusively with a dry food and other dogs. On the other hand, dogs that have a number of objects to chew present less calculus, fewer cases of gingivitis and less alveolysis than those that have few or no objects to chew (Harvey et al., 1996).

A dry food is potentially beneficial for dental hygiene if the shape and texture of the kibbles are specially designed for a particular size or breed of dog to contribute to passive tooth brushing mechanism. To scrape the surface of the tooth when the dog eats, the dog must chew so that the tooth penetrates the kibble deeply before the kibble breaks. Size and breed are two parameters that influence the pressure exercised on the kibble at the moment of prehension. Devices have been studied to test the kibble penetration threshold before fragmentation. This enables a comparison between various kibbles (Figure 10).

Figure 10. Force needed to break the kibble: comparison between two diffrent types of kibbles for small dogs. (Royal Canin, 2003). An elastic kibble that resists the pressure on it for longer before breaking enables the tooth to penetrate much deeper and so produces a more pronounced "cleaning" effect.

Control of Dental Hygiene with Food

The possibility of controlling dental plaque and the development of periodontal disease by the mechanical action of a chewing bone or specific foods was picked up on in the pet food industry in the early 1990s. Various studies were conducted on dogs with respect to dental plaque, calculus, coloration and gingivitis. Only dental plaque and gingivitis presented a medical interest. Dental coloration, important in humans for aesthetic reasons, is not of interest in dogs.

Royal Canin laboratory texturometer. The texturometer is used to measure the resistance of the kibble to the force of the dog's jaws and teeth. Interchangeable modules mimic the shape and the dimensions of the teeth of dogs of various ages and sizes.

A significant 19% reduction in dental plaque compared with the control group was obtained after one week of feeding with a kibble specifically targeting oral hygiene (Jensen et al., 1995). More recently, significant reductions of 39% in dental plaque and 36% in gingival inflammation were obtained after six months with the same food among dogs weighing 9 - 25 kg (Logan et al., 2002). In another study on the preventive effect of a daily food bone in dogs weighing an average of 23 kg, a significant reduction of dental plaque at 12 and 21 months (but not at 18 months) and gingivitis at 12, 18 and 21 months was observed (Gorrel & Bierer, 1999). Unfortunately, the reduction percentages are not given in this study, but an extrapolation based on the graphs show a maximum reduction of dental plaque and gingivitis of 15 - 20%.

The improvement of oral hygiene by food or dietary complement is accordingly a blossoming field. Besides the action on calculus, dental plaque and gingival inflammation must also be targeted. While the above results are very interesting, they have been obtained on medium-sized dogs, which is not at all the group most seriously affected by periodontal disease. Dogs weighing less than 8 kg are most seriously affected by periodontal disease. Studies must be conducted on specific breeds (Yorkshire Terrier, Poodle, Dachshund, etc) to verify whether the same results can be obtained. The author has conducted a study on 18 small dogs [average 7 kg] belonging to one of two groups depending on their genetic relationship. The test group that was given a dental chewing bar presented significant statistical reductions of 17% in dental plaque and 45% in calculus at the end of four months of study (Hennet, 2004).

The methodology of these studies has been questioned, mainly with respect to the evaluation of the dental plaque (Hennet, 1999; Harvey 2002). An improvement in the methodology could be considered to achieve results that are not only statistically significant but more importantly, biologically significant.

Example of a dental bar for small dogs that helps limit the accumulation of dental plaque and calculus. It is recommended that this type of complement be first given after scaling. The resistant yet elastic texture of this type of bar requires the dog to use its teeth to chew before swallowing.

Conclusion

We're witnessing a new era in veterinary nutrition. After mastering the food at the dietary level, the specific characteristics of the species and the various breeds must be given due consideration. Besides offering a good nutritional balance, the food can also play a role in preventing medical problems. Food with added value in oral hygiene and chewing bars that encourage mastication and have a texture that maximizes the self-cleaning effect contribute to reducing the accumulation of dental deposits and perhaps to preventing gingivitis. While daily brushing remains the best way of preventing periodontal disease, the complementary use of dental foods is recommended.