OBJECTIVES: Fixed orthodontic appliances are associated with higher levels of plaque and saliva bacteria, which contribute to dental caries. The effects of combining xylitol and fluoride, both used in caries prevention, are uncertain. Thus, this study assessed the combined impact of fluoride and xylitol varnish on bacteria in saliva and biofilms around orthodontic brackets. MATERIALS AND METHODS: A single-center, four-arm, parallel-group, triple-blind, randomized clinical trial was conducted. A total of 120 patients who required fixed orthodontic treatment were included. Patients were sorted into one of the following groups at random: fluoride, xylitol, combined fluoride and xylitol, and control. Biofilm and saliva sampling was performed at two intervals: T0 (first session of bracket bonding, before application of the varnish) and T1 (6 weeks after application of the varnish). The number of Streptococcus mutans and Lactobacillus was counted using the CFU method. RESULTS: The relative number of S. mutans and lactobacilli in saliva and biofilm significantly decreased following the application of fluoride and combined fluoride/xylitol varnish (p <
0.05) and were more effective than xylitol varnish. There was no significant difference between fluoride and combined fluoride/xylitol varnishes regarding changes in S. mutans and Lactobacillus colonies in saliva and dental biofilms. Additionally, there was no significant difference between xylitol and the two other active varnishes regarding reduction in biofilm S. mutans and Lactobacillus. CONCLUSION: There was no significant difference between fluoride and combined fluoride/xylitol varnishes regarding changes in the studied bacteria in saliva and dental biofilms, and they were more effective than xylitol varnish. TRIAL REGISTRATION: The Iranian Registry of Clinical Trial identifier: IRCT20181121041713N4
https://fa.irct.ir/trial/58543.