This study examined the effects of applying a 40% chlorhexidine varnish on dental plaque. 40 volunteers participated in a clinical trial where their plaque levels, gingival bleeding, and bacterial colony counts were measured after applying the varnish or not applying anything. The results showed that applying the chlorhexidine varnish significantly decreased plaque levels and gingival bleeding in volunteers with poor oral hygiene. It also reduced the frequency of high bacterial colony counts. The varnish was most effective at reducing plaque for patients with high baseline plaque levels. Regular application of chlorhexidine varnish can be an effective way to reduce caries risk for patients with poor oral hygiene.