Enamel hardness after exposure to acidic drinks and brushing

This study tested the hypothesis that short-term exposure to acidic drinks can reduce enamel surface hardness, and that subsequent brushing with toothpaste can cause detectable loss of enamel. Enamel specimens (three groups per storage medium) were immersed in one of four acidic drinks for five seconds, one minute, or 10 minutes. The pH values of all four drinks were measured. Six microhardness indentations were made on each specimen before immersion (baseline), after immersion, and after brushing with toothpaste. Changes in surface microhardness were expressed as the ratio of hardness values after each treatment to the baseline value of each specimen. Two-way ANOVA showed that both storage medium and duration of immersion influenced the ratio significantly. One-way ANOVA showed that the ratio was reduced significantly with increased time of immersion in drinks with a pH =2.8, but the ratio reduction was not significant in drinks with a pH =3.3. Subsequent brushing removed the softened layer and exposed intact surface underneath. Although short-term exposure (~5 seconds) did not significantly affect the surface hardness values, it left a lightly etched enamel surface among specimens immersed in acidic drinks with a low pH. Subsequent brushing could still cause detectable loss of enamel surface after multiple exposures.