The efficacy of mouthwashes on oral microorganisms and gingivitis in patients undergoing orthodontic treatment: a systematic review and meta-analysis

BACKGROUND: Mouthwashes were convenient adjuncts to mechanical cleaning procedures. This review aimed to evaluate the efficacy of mouthwashes on oral microorganisms and gingivitis in orthodontic patients. METHODS: By April 16, 2022, multiple databases and grey literature were searched based on the PICOS strategy. Randomized controlled trials in orthodontic patients evaluating the efficacy of mouthwashes with at least one microbial parameter and/or plaque- and/or gingival inflammation-related index were included. Relevant data were extracted, and the risk of bias was evaluated using Cochrane's tool. Individual mean and standard deviation of the outcomes in mouthwashes and placebos/blank controls were pooled to estimate the weighted mean differences (WMDs) and 95% confidence intervals (95%CIs). Sensitivity analysis, and certainty of evidence were evaluated. RESULTS: Of 1684 articles, 32 studies satisfied the eligibility criteria, and nine were included for meta-analysis. Missing outcome data was the primary source of bias. Compared to blank controls, the short-term application of fluoride mouthwashes significantly reduced the colony counts of Mutans streptococci (MS), while the long-term application may not be effective. Compared to placebos or blank controls, Chlorhexidine mouthwashes significantly reduced the colony counts of multiple microorganisms in the short-term. Compared to placebos or blank controls, herbal mouthwashes showed the inhibitory effect of MS in the short-term, with some results lacking statistical significance. After meta-analysis, significant lower plaque- and gingival inflammation-related indexes were observed in the Chlorhexidine mouthwashes groups [Gingival Index: WMD = -0.45, 95%CI = -0.70 to -0.20 (placebos as control); WMD = -0.54, 95%CI = -0.96 to -0.13 (blank controls); Plaque Index: WMD = -0.70, 95%CI = -1.12 to -0.27 (blank controls)]. Significant lower gingival inflammation-related indexes were observed in the herbal mouthwashes groups [Gingival Index: WMD = -0.20, 95%CI = -0.32 to -0.09 (blank controls)]. CONCLUSIONS: The short-term application of fluoride mouthwashes may reduce the colony counts of cariogenic bacteria, but the long-term effect is not evident. Chlorhexidine may reduce the colony counts of multiple microorganisms in the short-term. Short-term application Chlorhexidine and herbal mouthwashes may effectively reduce plaque- and gingival inflammation-related indexes. However, the risk of bias, inconsistency, and imprecision in the included studies may reduce the certainty of the evidence. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12903-023-02920-4.