The aim of this study was to investigate the effects of Cervitec Plus® on the level of mutans streptococcus (SM) and lactobacillus (LB) colonies and the development of white spot lesions (WSLs) in patients with fixed orthodontic appliances. Informed consent was obtained from 32 volunteers (age 16.5 ± 2.75 years). At baseline, levels of the bacterial colonies were determined in saliva and plaque using a chairside test (CRT Bacteria, Ivoclar-Vivadent, Schaan, Liechtenstein), and the number of WSLs was registered. After placing the fixed appliance, Cervitec Plus® or placebo varnishes (Ivoclar-Vivadent, Schaan, Liechtenstein) were applied monthly around the brackets and tubes, randomly in the right or left (test and placebo) quadrants of the same dental arch. SM and LB colonies in saliva and the SM colonies in plaque were determined on 11-21, 13-23, 15-25, and 16-26 teeth monthly over a 6-month period. At the sixth month, the number of new WSLs was determined. By the end of the study, compared with baseline, the ratio of saliva samples belonging to the low-risk category was significantly higher (p ≤ 0.01) from the 2nd month regarding the SM (76 vs. 52%) and LB (69 vs. 52%); reduction of SM in plaque was significantly greater on the test than placebo sides (6.69 ± 1.71 and 4.45 ± 1.60, respectively; p ≤ 0.01). The mean number of new WSLs was significantly lower in the test (0.06 ± 1.60) than in the placebo quadrants (1.13 ± 1.50, p ≤ 0.01). Monthly use of Cervitec Plus® could result in a significant improvement in oral health of orthodontic patients.