Cysteine challenge testing: a powerful tool for examining oral malodour processes and treatments in vivo.

Gram-negative oral bacteria rapidly produce the odorant hydrogen sulphide from cysteine. It provides a major part of the oral malodour bouquet while causing a corresponding decrease in the oxidation-reduction potential (Eh). A low Eh favours oral putrefaction and malodour occurrence. Challenge testing with cysteine (5ml of 6mM for 30 seconds) enabled evaluation of: the contribution of tongue and teeth bacteria to overall oral malodour; the effectiveness of tongue and tooth brushing, tooth scraping, gum chewing and mouthrinsing with different agents in reducing oral malodour. Successive cysteine challenge tests for 20 minute periods at selected times in a seven hour experiment were effective for assessing the magnitude and duration of an agent's effectiveness. Brushing the teeth reduced malodour modestly. So did tongue scraping and gum chewing. In contrast, brushing the tongue dorsum, especially the posterior half was remarkably effective, which confirmed it as a major site of oral malodour contribution. Rinses containing various actives showed wide variation in effectiveness. The experiments demonstrated that cysteine challenge testing is potentially a aluable tool for assessing the ability of the oral bacteria to produce malodour and for assessing agents designed to inhibit such production.

Role of saliva in oral dryness, oral feel and oral malodour.

Patients who believe they have oral malodour often have a dry mouth condition instead. Here we have examined its relation to oral malodour, real or perceived. A direct relationship between the thickness of the film of residual saliva on mucosal surfaces throughout the mouth and perception of a dry mouth was observed. On the hard palate, the thickness of this film proved to be diagnostic for a dry mouth and corresponded to lower resting saliva flow and pH levels (P< 0.001). Intra-muscular administration of the anti-sialogogue, Robinul, accurately produced the dry mouth condition. Using a sulphide monitor, loss of volatile sulphur compounds into mouth air progressively occurred as the mouth became drier. Mouth pH and Eh on the dorsum of the tongue correspondingly fell. Mouth breathing led to tongue and palate moisture loss thus enabling escape of malodour volatiles into mouth air. Measurement of oral dryness should make it possible to differentiate genuine malodour from dry mouth related pseudo-malodour subjects, and in turn, the latter from patients that are halitophobic. This should facilitate identification of such patients and avoid error in their clinical management.