Canine Oral Malodor

Introduction

Oral malodor can cause otherwise loving owners to push their pets away. It is a common condition in companion animals and a significant concern among owners.¹ Also known as halitosis or simply “doggy breath,” canine oral malodor can be a challenging problem. Significant malodor in the dog is not normal and may indicate a more serious disease process. Clients need to be cognizant of this early warning sign of oral disease.

The purposes of this paper are to review the common causes of canine oral malodor and present effective treatments for reducing the condition.

Origins

Oral malodor may or may not be oral in origin. Gastrointestinal disorders and systemic diseases, such as renal failure and respiratory infections, may account for some forms of oral malodor.^2,3 The most common source of bad breath, however, is the oral cavity itself.^1,2 Odors may originate from the products of microbial metabolism that accumulate on the oral soft tissues or tongue, or odors may arise from saliva and bits of food that are retained in the mouth.^2,3 Pathological conditions of the periodontal soft tissues and teeth can intensify the degree of oral malodor. Bacteria, especially gram-negative strains associated with periodontal disease, produce volatile sulfur compounds such as hydrogen sulfide and methylmercaptan, which contribute to the odor.³

In humans, it has been determined that most cases of offensive breath are of oral origin, and the majority of these cases can be improved with better oral hygiene.¹

Gas chromatography, flame photometric detection systems, portable meters measuring volatile sulfur compounds, and other systems have been used to quantify oral malodor in humans; however, some of these methods are not suitable for the measurement of malodor in dogs.¹

Association with Periodontal Disease

Periodontal disease affects the gingiva, supporting connective tissues, and the alveolar bone that surround and anchor the teeth in the jaws.⁴ Periodontal disease begins when the thin film of salivary proteins, normally present on the tooth surface, and dietary carbohydrates combine with bacteria to form plaque.⁴ If plaque is left undisturbed for ≥ 10 days, minerals in the saliva become incorporated into the plaque film, resulting in calculus or tartar.⁴ As bacteria and their by-products contact the gingiva, soft-tissue inflammation and destruction begin. The gram-positive bacterial flora yield to the more destructive gram-negative organisms as the infection moves deeper into the tissues.⁴ Compromised oral tissues, proteinaceous substances derived from food debris, exfoliated oral epithelial cells, gingival crevicular fluid, saliva, and blood all contribute to bacterial growth in the mouth.⁴ As a result, the number of epithelial cells and pathological bacteria increase in the mouths of dogs with periodontal disease.^2–4 It is these gram-negative bacteria that have been implicated in the production of volatile sulfur compounds, such as methyl mercaptans and hydrogen sulfide.² The production of volatile sulfur compounds correlates well with the activity of oral bacteria, which makes the measurement of these products useful in assessing periodontal disease.³

In a previous study, it was demonstrated that manipulation of the ingredients and texture in foods resulted in decreased levels of oral malodors in dogs, as determined by a panel of judges trained in sensory evaluation.¹ It was hypothesized that the reduction in malodor was directly related to improved oral hygiene, although a direct link was not determined.¹ In another study, daily toothbrushing resulted in a statistically significant reduction in oral malodor as measured by a sulfide monitor.⁵ Additionally, researchers found that oral malodor remained at a low level in a group of dogs that received a daily dental chew designed for reducing plaque and tartar buildup.^5,6 The results of these studies lend credence to the theory that general oral health is at least one factor affecting the degree of oral malodor.

Methods of Detection and Measurement

In dogs, the two most common methods for the detection of oral malodor are the use of a portable monitor (i.e., halimeter [see Figure]) that measures volatile sulfur compounds, and sensory evaluation. In human subjects, gas chromatography and photometric detection systems provide a quantitative measurement of offending compounds in the breath, but such equipment is somewhat difficult to adapt to dogs.^1,3,7 In many studies, humans are asked to breathe only through their noses for a period of time prior to each measurement, and then measurements are made with the subject exhaling air into a tube. Portable meters that measure sulfides in the oral cavity are somewhat easier to use in the dog but are generally less reliable than sophisticated analytical equipment.¹ Such meters primarily detect hydrogen sulfide and, to a lesser extent, other compounds such as methylmercaptan and dimethyl sulfide.³ Recently, a chemical sensor system, called an “electronic nose,” has been used in human subjects with promising results.⁸ Such devices were developed for quantitative measurement of odors and have been used in at least one human trial to objectively link oral malodor strength and oral health status.⁸

Sensory evaluation (i.e., direct sniffing and scoring of mouth air) has been the standard tool for evaluating the effects of a number of products, but it is somewhat subjective, and variations exist among judges in their perceptions and scoring of malodors.^1,9 Some of these variations can be minimized with proper training and instruction, so that the results are more reproducible and there is better correlation with objective measurements.^1,9

Fluctuations

In an attempt to explain variations in data from humans, one group of researchers precisely collected oral gases and utilized gas chromatographic analysis to evaluate the oral gas samples.¹⁰ Their findings supported the conclusion that the variability of concentrations of volatile sulfur compounds in the samples reflected actual biological events in the mouth.¹⁰ Frequent, periodic releases of gases by structures in the oral cavity were the apparent cause of these variations rather than simple laboratory error.¹⁰

In addition to possible fluctuations within the mouth, other natural phenomena may contribute to the degree of malodor detectable at any one time. For instance, as a dog ages, saliva production may decrease, which increases the likelihood of oral malodor. Halitosis is also often worse in the morning because of decreased flow of saliva during the night.³ Areas within the mouth that trap food and hair, such as exposed furcations, may contribute to an increase in offensive odors as bacteria putrefy within the warm, moist environment of the mouth.^2,11

Treatment and Prevention

A number of studies have supported the beneficial effects of improved oral hygiene in reducing canine oral malodor. Professional periodontal therapy has been shown to reduce malodor for up to 3 months in the dog.^2,7 Both daily toothbrushing and the use of a chlorhexidine rinse to reduce oral bacteria have been efficacious in preventing malodor.² Additionally, the act of chewing and the subsequent release of saliva can have a cleansing action on oral surfaces, resulting in less production of volatile sulfur compounds. Certain dental diets and chews may potentiate this effect.^2,5–7

Home-care products designed to reduce tartar and plaque buildup (and therefore malodor) are intended as an adjunct to professional dental care.⁵ Clients should be educated in the value of lifelong, proper professional oral prophylaxis and appropriate periodontal therapies so that the benefits of home-care products can be maximized. Steps to correct any underlying disease processes are absolutely essential, as home-care products are not designed to correct these problems but are intended to slow the progression of disease after the mouth has been professionally treated.

Conclusion

Canine oral malodor is a very common complaint. Owners are often unaware that treatment options exist for the condition, and they may neglect oral care until a significant amount of oral disease is present. Home-care products are designed to be adjunctive treatments and are not primary solutions for the rapidly progressive process of periodontal disease. Professional dental care administered by trained personnel remains the first line of defense in protecting dogs from the negative effects of oral disease.