Fluoride Absorption by Enamel from Toothpaste in Lowered pH Environment

Objectives: Calcium, vitamin D and fluoride may help patients with osteoporosis. A previous study has shown improved fluoride absorption from a fluoridated mouthrinse in a lowered pH environment. Effects of toothpaste fluoride absorption in a lowered pH salivary environment have not been established. The purpose of this investigation was to assess the fluoride absorption into enamel from a fluoridated toothpaste in an acidic salivary environment. Methods: Roots of 50 freshly extracted human teeth were masked and the crowns then immersed into experimental solutions. The solutions consisted of equal parts of synthetic saliva (Roxane Lab), with: a) distilled water, b) slurry mixture of Crest (Procter and Gamble), c) slurry mixture of Crest with amino acid lysine (calcium absorption facilitator), d) slurry mixture of Crest with citric acid pH 2, e) slurry mixture of Crest with citric pH 4, and f) slurry mixture of Crest with lysine pH 4. After crown immersion for periods of 1 and 5 min, the teeth were removed and the solutions subjected to fluoride concentration analysis using a fluoride ion activity electrode technique. The amount of fluoride absorbed by the crowns was determined by subtracting the amount of fluoride in solution prior to and following crown immersion. The data was subjected to ANOVA and t tests. Results: Lowered pH in a salivary environment significantly enhanced fluoride absorption from the toothpaste compared to a neutral pH environment (p < 0.05). There was no fluoride absorption differences observed between pH levels or immersion times. Some increase of fluoride uptake was noted with groups containing lysine. Conclusions: This study indicates that lowered pH in a salivary environment increases fluoride activity for significantly greater fluoride absorption from toothpaste containing fluoride into enamel, with psssible benefits to osteoporosis patients. Further, lysine causes some increase in fluoride absorption into enamel.