Ultrasonic Enhancement of Fluoride Uptake into Hydroxyapatite

Objective: Enhancing the acid resistance of enamel lesions promoted by fluoride treatments is important for the prevention of dental caries as well as for maintaining good oral health. The acceleration of chemical reactions using ultrasound is expected for improving the effects of medicines. The purpose of this study is to enhance a fluoride uptake effect for the prevention of dental caries under ultrasound irradiation. Methods: Fluoride uptake into hydroxyapatite was experimentally measured for four kinds of NaF aqueous solutions (1,000, 2,500, 5,000 and 9,000 ppm F) under the conditions with and without ultrasound irradiation. A PZT-family piezoelectric ceramic plate with a rectangular shape of 7.0 x 20.5 mm² (Fuji Ceramic Co.) was used for generating a longitudinal wave beam in NaF aqueous solution contained in a plastic capsule via a water tank. Hydroxyapatite samples (Pentax, Apaceman APP-100) were classified into two groups for the F uptake testing for 3 minutes of immersion with and without ultrasound. The data were statistically analyzed by ANOVA. Results: The fluoride uptake in 9,000 ppm F aqueous solution under 2.25 MHz ultrasound was significantly higher than those in other groups (p<0.01), which was improved by 74 % compared with the result of no ultrasound. The amount of fluoride uptake in 5,000 ppm F aqueous solution with ultrasound was as high as that in the 9,000 ppm F aqueous solution without ultrasound. Conclusion: The present ultrasonic method is promising for increasing fluoride uptake for promoting the acid resistance of enamel lesions and has the merit of safety in the human aural cavity under a low voltage supply to an ultrasonic transducer and has a potential use for in vivo dental caries prevention.