Although the dorsum of the tongue harbors one of the most complex microbiological niches in human ecology, information on the relationship of tongue flora with health and disease is very limited. Similarly, the nature of the tongue coating and the factors that influence its development and composition are almost unknown. Recently, the agents that cause oral malodour have been identified. These agents include volatile sulfur compounds, propionic acid, butyric acid, cadaverine, putrescine, indole, skatole, etc., and especially, hydrogen sulfide and methyl mercaptan. Furthermore, these substances had a significantly positive correlation with tongue biofilms. Tongue coating can be successfully managed by combining mechanical cleaning(brushing, tongue brushing, tongue scraping) and various chemical solutions. This combination can effectively reduce bad breath. The purpose of this review is to evaluate the present knowledge in tongue niche and tongue coating by focusing on the microbiology of the tongue biofilm. Special emphasis will be given on the evaluation of the evidence linking tongue biofilm with oral halitosis.
