The purpose of the investigation was to determine the effect of drinking a natural mineral dietary supplement (NMDS) on gingival health and dentinal hypersensitivity. The NMDS product was from a geothermal source and contained 3.6 mg l−1 of fluoride and other minerals. Sample selection included subjects with gingival inflammation and sensitivity as well as screening for exclusion factors. A double-blind randomized parallel approach was used. The investigation was a quasi-experimental pre/post-test design. The experimental group ingested and swished twice a day with the NMDS (1 l) and the control group followed the same regimen with a placebo containing de-ionized water (DIW). Clinical measurements of gingival inflammation and dentinal sensitivity were taken at baseline, 4 and 8 weeks. Gingival inflammation was measured using the Gingival Index. Dentinal hypersensitivity was measured using a tactile stimulus and an evaporative stimulus. After each stimulus was applied, the subjects rated the amount of discomfort on a visual analogue scale from 0 to 10. Each set of data was analysed using ANOVA and a post hoc probing technique to determine within- and between-group differences (P = 0.05). The experimental and control groups (n = 70) experienced a statistically significant decrease in tactile and evaporative sensitivity scores over time; however, the between-group differences were not significant. The gingival inflammation data were not statistically significant with regard to the within- and between-group differences. Therefore the NMDS and DIW were equally effective in reducing dentinal hypersensitivity and neither product effectively reduced gingival inflammation.