Oral malodor
Volatile sulfur compounds
The key components of oral malodor are reported to be VSCs produced by bacteria in the mouth. [Awano et al, 2002] It has been calculated that there are around 500 species of bacteria present in dental plaque and 600 on the surface of the tongue. [Paster et al., 2001; Kazor et al., 2003]
VSC production is commonly associated with bacterial metabolism, particularly the digestion of proteins by gram-negative bacteria. These proteins are derived from food, shedding mucosa, saliva and gingival crevicular fluid.
VSCs considered to be the main components of oral malodor are hydrogen sulfide, methyl mercaptan and dimethyl disulfide. However, several other compounds have been reported to contribute to oral malodor and include putrescine, cadaverine, indole, skatole and butyric and propionic acids, although these are not readily quantifiable. [Moss, 1998]
The role of bacterial metabolism in oral malodor
VSCs in the oral cavity
For around 90% of patients, oral malodor originates in the mouth. [Rosenberg et al, 2002; Delanghe, 1997] The most common sites associated with harboring VSC-producing bacteria are the tongue, interproximal areas and below the gum line (in dental plaque). [Rosenberg, 1996; Lee et al., 2003; Figueiredo et al., 2002]
The rear portion of the tongue is a particular harbor for anaerobic bacteria, with its large surface area and crevices. Studies analyzing scrapings from the tongue surface have demonstrated a significant relationship between oral malodor and the levels of bacteria on the tongue. In particular, the levels of those anaerobic bacteria associated with the breakdown of proteins in the diet are known to correlate with the level of oral malodor. [De Boever et al., 1995; Lee et al., 2003]
Factors that influence oral malodor
Levels of VSCs in the breath vary greatly between individuals and also at different times during the day. This is because bacteria responsible for oral malodor are influenced by eating, drinking, oral hygiene and sleep.
The natural flow of saliva within the mouth facilitates the clearing away of bacteria. During sleep, when there is a reduced flow of saliva in the mouth, bacteria build up leading to oral malodor first thing in the morning. [Rosenberg, 1996] Alcohol and cigarettes dry out the mouth, reducing saliva flow and exacerbating the problem. [Scully, 1994]
Oral malodor may also be linked to the development of gum disease, as poor oral hygiene may lead to tooth cavities, gum disease and oxygen-deprived pockets within the mouth that provide spaces for anaerobic bacteria to live in. [Moss, 1998; Ratcliff et al., 1999; Lee et al., 2003]
Other causes of malodor
In addition to oral malodor produced by bacteria within the mouth, other causes of oral malodor have been identified. Transient oral malodor may be caused by strong-smelling foods like curry, garlic and onions which are broken down into unpleasant-smelling compounds that are exhaled for up to 24 hours after consumption. [Scully et al., 1994] Medical conditions such as respiratory, liver and kidney diseases may also be linked with oral malodor. [ADA, 2003] A small number of the population suffer with ‘halitophobia’, where the subject complains of halitosis, but this is not detected by others. In these cases psychiatric referral may be required.
