The oral cavity as a bioreactor in halitosis

Halitosis is a prevalent yet often underestimated clinical condition with multifactorial etiology, predominantly arising from intra-oral sources such as periodontal disease, tongue coating and xerostomia. Central to its pathogenesis is the microbial degradation of sulfur-containing substrates, which lead to the production of volatile sulfur compounds and other volatile organic compounds responsible for the characteristic odor. These metabolites are produced by proteolytic anaerobes inhabiting the tongue dorsum, periodontal pockets as well as the dental plaque and predominantly exist as structured biofilms. This review examines halitosis through a systems-based lens, conceptualizing the oral cavity as a dynamic bioreactor governed by microbial consortia and their metabolic pathways, mass transport, enzymatic kinetics, as well as growth conditions attributed to microenvironmental factors. Modeling approaches are required to elucidate the intricate dynamics within oral biofilms, including the heterogeneous structural organization and the fundamental transport and metabolic processes occurring at the biofilm-bulk fluid interface and within the biofilm matrix. These interfacial processes, in turn, regulate the flux of volatile compounds into the oral air. Furthermore, associations between halitosis and dental pathologies, including gingivitis, periodontitis, and periodontal abscesses, are explored through microbial dysbiosis. The review also addresses contemporary management strategies including mechanical debridement, antimicrobial agents and probiotics. Understanding the biochemical, microbial and reactor-like behavior of the oral cavity is critical for the effective diagnosis, monitoring and treatment of halitosis in clinical and research settings.