A study on changes in caries risk and microbial flora with the placement of edgewise appliance

The aim of this study was to evaluate the changes of caries risk and oral microbial flora in the patients having edgewise appliance. Forty-two patients treated at the Orthodontic Clinic of Niigata University Hospital participated. Using a caries risk examination kit by Bio Medical Laboratory (BML, Tokyo), stimulated saliva test was performed to investigate the salivary flow rate, pH of saliva, buffer capacity, and the levels of lactobacilli. Modified Mitis–Salivarius–Bacitracin (MSB) agar plates were used to detect and count Streptococcus mutans and S. sobrinus. Furthermore, the members of commensal bacteria and transient bacteria in aerobic culture medium were examined in salivary level to investigate the alterations in oral microbial flora. The number of mutans streptococci and lactobacilli decreased after 1 month of treatment, and then increased to reach the initial level at 3 months. While the amount of plaque increased and saliva pH deteriorated after the onset of treatment, the salivary flow rate improved. The number of transient bacteria showed a tendency toward an increase. These results demonstrate that both caries risk and oral microbial flora balance possibly change with the placement of appliances. Therefore, caries risk test should be performed before and during orthodontic treatment to monitor alterations in intraoral environment of the orthodontic patients not to cause an iatrogenic caries.