Clinical studies that evaluated the effect of chlorhexidine solutions, gels or varnishes on mutans streptococci levels were eligible for inclusion. Studies that lacked data on reduction in mutans streptococci levels over time were excluded, as were those in which the intervention included other preventative methods (such as dental hygiene guidance, use of fluoride and intensive professional prophylaxis) or which involved no prior restorative treatment.
The review included studies of chlorhexidine solution (at concentrations of 0.025% to 0.2%, 4mL to 15mL used as a rinse for 30 to 60 seconds up to four times daily for up to six weeks), gel (at concentrations of 0.2% to 1%, applied daily by toothbrush for seven to 14 days or at 1% to 5% concentration applied by one or two intensive professional treatments) and varnish (at 1% to 40% concentrations, professionally applied two to four times over two to seven days or at intervals of 30 days or more).
Inclusion criteria for study populations varied widely (for example, dental students, mutans streptococci colonisation, presence of orthodontic appliance, eruption of first molars and good oral health). Participant ages ranged from 10 months to 98 years. The included studies reported reduction in decreased salivary or dental biofilm levels of mutans streptococci. Interventions were compared with different doses or formulations of chlorhexidine, placebo (such as saline, flavoured/coloured water) or no treatment.
The authors stated neither how the papers were selected for the review nor how many reviewers performed the selection.