Introduction: Traumatic oral lesions are common in the beginning of the orthodontic treatment, and pathogenic oral bacteria might be involved. We tested whether the probiotic Lactobacillus brevis CD2 (L brevis) is benefic in this condition. Methods: In a double-blind clinical trial, 20 patients were randomized to 21 days course of lozenges containing L brevis CD2 (4 billion colony-forming units after breakfast, lunch and dinner) or placebo, starting on the day of installation of the fixed orthodontic appliance. Main outcomes were days without oral lesions and oral pain score [ranging between 0 (no pain) and 10 (maximum)]. Oral health related quality of life was measured by OHIP-14 before and after treatments.

Study protocol After signing the informed consent form, the patients underwent an oral examination and answered about clinical information, oral pain scale, and the OHIP-14 questionnaire. The pain scale was graded between 0 (no pain) and 10 (maximum), Likert standard. There was also a drawing for the distribution of coded treatments, through a number taken by the patient from a manila envelope. After the orthodontic appliance installation session, each patient was instructed to use the coded treatment for the next 21 days, two gums after breakfast, after lunch and after dinner, totalizing 12 billion UFC of L brevis or placebo per day. The patient was provided with a diary to note the daily appearance of lesions and their evolution during the 21-day period, as well as the occurrence of any new symptoms (potential adverse effect), in addition to proof of the commitment assumed by the use of the tablets. After 21 days, each patient was reexamined by the author of the study, who collected the diaries and obtained information regarding the oral examination, oral pain scale, data on adherence to treatment and self-completion of the OHIP-14.

Statistical analysis Quantitative data are described with mean and standard deviation (or standard error of the mean) or median and range, while qualitative data are displayed with absolute and relative frequencies. Student's t-test was used for comparison of quantitative data between groups, Wilcoxon-Mann-Whitney (WMW) test being employed when the assumptions for that test were not met. Exact chi-square and Fisher´s exact test (FET) were used for categorical data. Treatment effect on OHIP-14 was analyzed using a Generalize Estimating Equations (GEE) model with Poisson distribution and log link, the predictors being treatment, time (beginning and end of treatment) and interaction treatment*time. The analyses were performed with softwares GraphPrism version 4.0 and SPSS® (IBM SPSS statistics v18). Sample size was estimated using WinPEPI v11.65. The P value indicative of significance was < 0.05. Because the final outcome was prevention or mitigation (not maintenance or augmentation) of undesirable symptoms, one-tailed tests were used for comparisons between groups respect to days without oral lesions, oral pain and OHIP-14 scores.

Inclusion Criteria:

• need for orthodontic treatment with fixed appliance

Exclusion Criteria:

• Oral lesions
• Uncompensated systemic diseases
• Regular use of corticoids, antibiotics, immuno regulators and antidepressive agents

Patients were treated with identical lozenges containing probiotic or placebo. The treatments were revealed only after statistical analysis.