Objectives The primary objective was to determine the erosive effect of expectorated saliva, following chewing acidic gum, on enamel and dentine samples, using a non-acidic gum as a negative control. Secondary objectives were to determine the effect of brushing enamel and dentine samples and the effect of individual saliva pH and buffering. Design A single-centre, single-blind, placebo-controlled, two-way crossover study. Setting A clinical trial, involving healthy participants, undertaken at Bristol Dental School and Hospital. Methods Eight healthy participants expectorated saliva onto prepared enamel and dentine samples while chewing gum (strawberry flavoured acidic gum [active] or peppermint flavoured non-acidic gum [control]). Half of the enamel and dentine samples were brushed before measurement by contact profilometry. Main outcome measures Mean enamel and dentine erosion, with and without brushing and the relationship to salivary buffering. Results At 10 days, mean depth of surface loss from dentine samples (95% CI), following chewing of acid-containing gum and subsequent brushing, was -11.34 mu m (2.22 mu m) and from un-brushed dentine samples was -11.02 mu m (1.71 mu m). No significant erosion was noted for other groups. Conclusions Frequent chewers of acid-containing gums are susceptible to dentine erosion even in the presence of good salivary buffering. Enamel erosion was insignificant within the time constraints of the present study but warrants further investigation.