Dental caries is one of the commonest diseases in the world1 yet is almost completely preventable with a combination of oral hygiene using anticariogenic agents, typically the use of fluoride, and dietary measures. As acidogenic bacteria in dental plaque cause local demineralisation of the tooth that can lead to cavity formation there is the potential for antibacterial agents to contribute to caries reduction.

Chlorhexidine gluconate (a cationic bis-biguanide) has been used for many years as an antiplaque agent and has been shown to suppress Streptococcus mutans, so could be used for caries prevention. A number of chlorhexidine preparations are available, as toothpastes, gels, thymol-containing varnishes, chewing gums and sprays. This Cochrane review aimed to assess the effectiveness of these chlorhexidine-containing oral products on caries prevention in children and adolescents.

Only randomised controlled trials were considered for the review with the exclusion of split mouth RCTs as there is considerable potential for cross contamination. Standard Cochrane protocols for the conduct of the review were planned and followed where sufficient data were available.

The eight included trials were reported in 12 publications. Two of the trials were cluster design with randomisation at the school class level but these trials' authors did not take this clustering into account in their analysis. The review authors re-analysed these studies to take into account the clustering using a range of intraclass correlation coefficients.

A range of chlorhexidine preparations was used in the studies; 1%, 10%, 40% chlorhexidine varnish, each with a different application regimen, and chlorhexidine gel with a concentration of 0.12%. Most of the trials were considered to be at high risk of bias (six out of eight) and none at low risk of bias.

The review authors assessed the overall quality of evidence according to GRADE (Grading of Recommendations Assessment, Development and Evaluation) considering it to be of very low quality.

No studies were found assessing chlorhexidine-based mouthrinses, toothpastes, chewing gums or sprays for the prevention of dental caries in children and adolescents and half of the included studies did not report adverse events. As there is a number of known adverse events that included staining of the teeth and tongue, mucosal soreness and desquamation, temporary taste disturbances, parotid gland swelling and hypersensitivity (including anaphylaxis) this is of concern.

At present there is little evidence that chlorhexidine could provide an alternative approach to caries prevention as there is good evidence for the use of topical fluorides in varnish, toothpastes, gels and mouthrinses2 as well as fissure sealants,3 so these approaches should be prioritised for caries prevention.