Oral Malodour

The basic causes of oral malodour are now fairly well understood. There are different degrees of oral malodour, and some situations are part of normal physiology.

1. Morning breath

When oral malodour is common on awakening (so called morning breath), this is usually a consequence of low salivary flow and stagnation during sleep. This complaint can be higher in mouth breathers and may be exacerbated by other oral causes of malodour. If this is the case, oral malodour may be readily rectified by eating, tongue brushing, tooth brushing and rinsing the mouth with fresh water. Hydrogen peroxide rinses will also eliminate this odour.

2. Exogenous malodour

Various foods such as garlic, onion, durian, cabbage, Brussel sprouts, cauliflower or raddish, spices such as in curries, as well as habits such as tobacco or alcohol can cause bad breath. Avoidance of these foods and habits is the best mean of prevention.

3. True oral malodour (endogenous malodour)

When oral malodour is not associated with the factors already described, it is most often a consequence of oral bacterial activity, typically from anaerobes. There are many reasons for this bacterial activity, first of all poor oral hygiene.

However, some bad breath seems to be associated with local pathological causes, such as gingivitis (especially ANUG), periodontal disease, infected extraction sockets, or other types of oral sepsis.

In some cases, other possibilities that favour oral malodour are the presence of residual blood post-operatively, debris under bridges or appliances, ulcers, dry mouth and putrefaction of postnasal mucus drip stagnating on the tongue.

The large surface of the tongue and its papillary structure retain a consistent number of food debris and are often the location of the micro-organisms implicated which are predominantly Gram-negative anaerobes, and include Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum, Bacteroides forsythus and Treponema denticola.

In many instances, these bacteria release chemicals that produce malodour, which include volatile sulphur compounds (VSC) such as hydrogen sulphide and methyl mercaptan, but also diamines like cadaverine and putrescine and short chain fatty acids (butyric, valeric and propionic).

Recently, Gram-positive bacteria have also been implicated since they can denude the available glycoproteins of their sugar chains, enabling the anaerobic Gram-negative proteolytic bacteria to break down the denuded proteins, resulting in the chemicals described above. On the other hand, the evidence for the implication of other micro-organisms, such as Helicobacter pylori, is scant.

Smoking may increase the production of some of these odiferous compounds and smoke itself contains thousands of volatiles.

In the absence of oral causes, systemic conditions may be responsible for oral malodour, including starvation, drugs causing dry mouth, drugs like cytotoxic agents, dimethyl sulphoxide, disulfiram, nitrites/nitrates and solvent abuse.

A part from local causes, the most common source of bad breath is the nose and its passages. Respiratory diseases that should be ruled out include nasal sepsis or foreign bodies, paranasal sinus infection, tonsillar infection, lower respiratory tract infection and infected tumours in the respiratory tract.

Other systemic causes of halitosis are less common and they include diseases such as diabetes mellitus and gastrointestinal diseases. Gastroesophageal reflux disease (GERD) may occasionally underlie halitosis, as well as hepatic failure and renal failure.

One interesting but rare situation is trimethylaminuria (TMAU; fish malodour syndrome). Trimethylamine (TMA) is present in the diet or can derive from the intestinal bacterial degradation of foods such as fish, eggs and some legumes rich in choline and/or carnitine. TMA is normally oxidized by the liver to the odourless trimethylamine-N-oxide (TMAO) which is then excreted in the urine. Inherited mutations of the gene for a liver drug-metabolizing enzyme (the flavin-containing monooxygenase 3 - FMO3)) accounts for a severe recessive form of trimethylaminuria in which there is impaired oxidation of TMA. The unoxidized TMA is excreted in urine, sweat, vaginal secretions, saliva and breath. Rarely a similar problem can arise due to congenital liver disorder with portal-systemic shunting due to an unusual intrahepatic vascular connection.

Halitophobia is a psychogenic condition. In these patients, no evidence of halitosis can be detected even with objective testing, and the condition may be attributable to a form of delusion of monosymptomatic hypochondrias.