Background: The purpose of the present investigation was to determine the effect of the absence of tongue hygiene on the microbiota of the dorsum of the tongue.

Methods: Ten volunteers (aged 19 to 22 years) entered the study at baseline and were instructed to abstain from tongue cleaning for 7 days, followed by a period of 3 days without any kind of oral hygiene. Subsequently, a period of 21 days of washout was employed, and this protocol was repeated three times. Microbiological samples were obtained from the dorsum of the tongue at baseline and at the end of the period of coating accumulation and analyzed using the checkerboard DNA-DNA hybridization technique.

Results: The species found in highest mean counts at baseline and day 10 were Prevotella melaninogenica and Veillonella parvula. The mean bacterial total counts enhanced significantly during the study (from 17.1 × 10⁶ to 33.7 × 10⁶). Proportions of red and blue complexes and levels of 18 species also increased after the period of coating accumulation, including several periodontal pathogens, such as Prevotella intermedia, Prevotella nigrescens, Streptococcus constellatus, Tannerella forsythensis, Porphyromonas gingivalis, Treponema denticola, and P. melaninogenica.

Conclusion: The tongue surface could be an important reservoir for periodontal pathogens and may play a role in the recolonization of tooth surfaces and in the etiology of oral halitosis.