Development and applications of models of oral maladour

Halitosis (oral malodour) while not a classic disease is prevalent and can be socially disabling; thus studying the origins and control of malodour are socially and commercially important. Volatile sulfur compounds (VSCs) are important contributors to halitosis, and can be combated by adding zinc to oral care products. The aims of the thesis were to develop a model system to grow mixed culture, tongue-derived microbial biofilms in vitro. This model was used to investigate the efficacy of zinc as a VSC-reducing and antimicrobial agent, as well as visualising the distribution and retention of zinc within the biofilms. A perfusion biofilm model (PBM) was established with sorbarod filters as a microcosm representing the tongue. Treatments with zinc toothpaste, placebo toothpaste, zinc sulfate solution (ZnSO4) and deionised water were assessed using a portable gas chromatograph (OralChromaT'V'), microbiological assays, confocal microscopy and inductively coupled plasma-mass spectrometry (lCP- MS). Zinc significantly reduced hydrogen sulfide concentrations but had a moderate effect on methanethiol. The zinc and placebo toothpaste exhibited bacteriostatic effects, confirmed by plate counting and confocal live-dead images. Zinc was retained and visible to a greater extent in the zinc toothpaste treated biofilm compared to ZnSO4 solution; distribution varied markedly between biofilm layers and replicates. lCP-MS confirmed presence of zinc. PBM was shown to be a suitable model for studying sources of oral malodour. Zinc reduced VSCs, probably by binding sulfur compounds forming insoluble zinc sulfides; zinc had a bacteriostatic effect, potentially due to metabolic inhibition, which was increased by other toothpaste ingredients. The varied distribution of zinc reflected the heterogeneity and complexity in the architecture of mature biofilms. In conclusion, zinc had multifactorial effects on VSCs, including antimicrobial and VSC reducing. Retention of zinc was visible, however with variations in distribution within the biofilms. Further work is needed; including conducting human microbe identification microarrays.