Diurnal variation of salivary anaerobes correlates severe dental caries in children

Background: Salivary secretion has diurnal fluctuations and the saliva amount affects oral bacterial activity. In this study, the time dependence of number of anaerobic bacteria in saliva such as Streptococcus mutans (S. mutans) was investigated and examined its impact on caries severity. Methods: This study was conducted at university hospital in Japan. Twenty subjects (2-10 years old) with the primary dentition were asked to collect whole saliva every 1 hour after the supper while awake at home. Eighteen subjects delivered the collected saliva, which was cultured for S. mutans and total anaerobes in trypticase-yeast extract-cysteine sucrose-bacitracin (TYCSB) medium and the Gifu anaerobic medium (GAM), respectively. The numbers of severe dental caries were also analyzed from medical records. Results: A positive correlation was found between the number of colonies in GAM medium and the saliva collection time of the day. No significant correlation was observed between the number of colonies in TYCSB medium and the collection time. The patients were grouped based on whether or not they had experienced pulp treatment. The number of colonies of S. mutans and anaerobic bacteria were increased in the later hours of only the experienced group. Conclusions: The number of oral anaerobic bacteria of children fluctuated in time-dependent manner after dinner to bedtime, and was higher late in the night. Children with severe dental caries had increased S. mutans as the night progressed, whereas children without them did not.