Abstract: We included eight RCTs that evaluated the effects of chlorhexidine varnishes (1%, 10% or 40% concentration) and chlorhexidine gel (0.12%) on the primary or permanent teeth, or both, of children from birth to 15 years of age at the start of the study. The studies randomised a total of 2876 participants, of whom 2276 (79%) were evaluated. We assessed six studies as being at high risk of bias overall and two studies as being at unclear risk of bias overall. Follow-up assessment ranged from 6 to 36 months. Six trials compared chlorhexidine varnish with placebo or no treatment. It was possible to pool the data from two trials in the permanent dentition (one study using 10% chlorhexidine and the other, 40%). This led to an increase in the DMFS increment in the varnish group of 0.53 (95% confidence interval (CI) -0.47 to 1.53; two trials, 690 participants; very low quality evidence). Only one trial (10% concentration chlorhexidine varnish) provided usable data for elevated mutans streptococci levels > 4 with RR 0.93 (95% CI 0.80 to 1.07, 496 participants; very low quality evidence). One trial measured adverse effects (for example, ulcers or tooth staining) and reported that there were none; another trial reported that no side effects of the treatment were noted. No trials reported on pain, quality of life, patient satisfaction or costs. Two trials compared chlorhexidine gel (0.12% concentration) with no treatment in the primary dentition. The presence of new caries gave rise to a 95% confidence interval that was compatible with either an increase or a decrease in caries incidence (RR 1.00, 95% CI 0.36 to 2.77; 487 participants; very low quality evidence). Similarly, data for the effects of chlorhexidine gel on the prevalence of mutans streptococci were inconclusive (RR 1.26, 95% CI 0.95 to 1.66; two trials, 490 participants; very low quality evidence). Both trials measured adverse effects and did not observe any. Neither of these trials reported on the other secondary outcomes such as measures of pain, quality of life, patient satisfaction or direct and indirect costs of interventions. We found little evidence from the eight trials on varnishes and gels included in this review to either support or refute the assertion that chlorhexidine is more effective than placebo or no treatment in the prevention of caries or the reduction of mutans streptococci levels in children and adolescents. There were no trials on other products containing chlorhexidine such as sprays, toothpastes, chewing gums or mouthrinses. Further high quality research is required, in particular evaluating the effects on both the primary and permanent dentition and using other chlorhexidine-containing oral products.

Plain-language summary: The evidence in this review, carried out through the Cochrane Oral Health Group, is up-to-date at 25 February 2015. We found eight studies that were suitable to include in this review. The studies involved a total of 2876 children from birth to 15 years of age who were at moderate to high risk of tooth decay. Six of the studies looked at the effects of dental professionals applying different strengths of chlorhexidine varnishes to the baby teeth, permanent teeth or both types of teeth in children and adolescents. The other two studies looked at the effects of parents placing chlorhexidine gel on their children's baby teeth. There were no studies that examined other products containing chlorhexidine, such as sprays, toothpastes, chewing gums or mouthrinses. The results did not provide evidence that chlorhexidine varnish or gel reduces tooth decay or reduces the bacteria that encourage tooth decay. The studies did not evaluate other outcomes such as pain, quality of life, patient satisfaction or direct and indirect costs of interventions. Four studies measured side effects and found none were observed. Due to the lack of suitable studies and concerns about possible bias in the included studies, the evidence is very low quality. As a result, we are not able to conclude whether or not chlorhexidine is effective in preventing tooth decay in children or adolescents, when compared to placebo (an inactive substitute for chlorhexidine) or no treatment. Future research on the use of chlorhexidine to prevent tooth decay is needed and should consider both primary and permanent teeth and should assess other chlorhexidine-containing products that can be used at home, such as toothpastes or mouthrinses.