Abstract: We included 51 studies that analysed a total of 5345 participants. One study was assessed as being at unclear risk of bias, with the remaining 50 being at high risk of bias, however, this did not affect the quality assessments for gingivitis and plaque as we believe that further research is very unlikely to change our confidence in the estimate of effect. Gingivitis After 4 to 6 weeks of use, chlorhexidine mouthrinse reduced gingivitis (Gingival Index (GI) 0 to 3 scale) by 0.21 (95% CI 0.11 to 0.31) compared to placebo, control or no mouthrinse (10 trials, 805 participants with mild gingival inflammation (mean score 1 on the GI scale) analysed, high-quality evidence). A similar effect size was found for reducing gingivitis at 6 months. There were insufficient data to determine the reduction in gingivitis associated with chlorhexidine mouthrinse use in individuals with mean GI scores of 1.1 to 3 (moderate or severe levels of gingival inflammation). Plaque Plaque was measured by different indices and the SMD at 4 to 6 weeks was 1.45 (95% CI 1.00 to 1.90) standard deviations lower in the chlorhexidine group (12 trials, 950 participants analysed, high-quality evidence), indicating a large reduction in plaque. A similar large reduction was found for chlorhexidine mouthrinse use at 6 months. Extrinsic tooth staining There was a large increase in extrinsic tooth staining in participants using chlorhexidine mouthrinse at 4 to 6 weeks. The SMD was 1.07 (95% CI 0.80 to 1.34) standard deviations higher (eight trials, 415 participants analysed, moderate-quality evidence) in the chlorhexidine mouthrinse group. There was also a large increase in extrinsic tooth staining in participants using chlorhexidine mouthrinse at 7 to 12 weeks and 6 months. Calculus Results for the effect of chlorhexidine mouthrinse on calculus formation were inconclusive. Effect of concentration and frequency of rinsing There were insufficient data to determine whether there was a difference in effect for either chlorhexidine concentration or frequency of rinsing. Other adverse effects The adverse effects most commonly reported in the included studies were taste disturbance/alteration (reported in 11 studies), effects on the oral mucosa including soreness, irritation, mild desquamation and mucosal ulceration/erosions (reported in 13 studies) and a general burning sensation or a burning tongue or both (reported in nine studies). There is high-quality evidence from studies that reported the Löe and Silness Gingival Index of a reduction in gingivitis in individuals with mild gingival inflammation on average (mean score of 1 on the 0 to 3 GI scale) that was not considered to be clinically relevant. There is high-quality evidence of a large reduction in dental plaque with chlorhexidine mouthrinse used as an adjunct to mechanical oral hygiene procedures for 4 to 6 weeks and 6 months. There is no evidence that one concentration of chlorhexidine rinse is more effective than another. There is insufficient evidence to determine the reduction in gingivitis associated with chlorhexidine mouthrinse use in individuals with mean GI scores of 1.1 to 3 indicating moderate or severe levels of gingival inflammation. Rinsing with chlorhexidine mouthrinse for 4 weeks or longer causes extrinsic tooth staining. In addition, other adverse effects such as calculus build up, transient taste disturbance and effects on the oral mucosa were reported in the included studies.

Plain-language summary: We included 51 studies that analysed a total of 5345 participants. The evidence in this review is up to date as of 28 September 2016. Generally study participants were children and adults who had gingivitis or periodontitis, were able to use usual tooth cleaning methods and were healthy. We did not exclude studies where some or all participants had medical conditions or special care needs as we considered the use of mouthrinses with chlorhexidine to be particularly relevant to them. The included studies assessed the effects of chlorhexidine mouthrinse used for at least 4 weeks in addition to conventional tooth cleaning on gingivitis in children and adults. There is high-quality evidence that the use of mouthrinses containing chlorhexidine in addition to usual toothbrushing and cleaning for 4 to 6 weeks or 6 months leads to a large reduction in the build-up of plaque. There is also high-quality evidence of a moderate reduction in gingivitis in people with a mild level of it, although because the level of disease was already low this is not considered clinically important. The nature of the available evidence does not allow us to determine the level of reduction of gingivitis in people with moderate to severe levels of it. There was no evidence that one concentration or strength of chlorhexidine rinse was more effective than another. Rinsing for 4 weeks or longer causes tooth staining, which requires scaling and polishing carried out by a dental professional. Other side effects have been reported, including build-up of calculus (tartar), temporary taste disturbance and temporary shedding of/damage to the lining of the mouth. One study was assessed as being at unclear risk of bias, with the remaining 50 being at high risk of bias, however this did not affect the quality assessments for gingivitis and plaque as we believe that further research is very unlikely to change our confidence in the estimate of effect.