In vitro fluoride dose-response study of sterilized enamel lesions

Currently our intra-oral model uses enamel specimens that have been disinfected by soaking in buffered formalin (pH 6.8). However, because of increasing emphasis on infection control, it is important to identify a way to sterilize these specimens. The aim of this study was to determine if autoclaved, or gas sterilized, lesioned enamel responds to fluoride (F) in the same way alcohol-disinfected enamel lesions do. Seventy-two formalin-disinfected, human enamel specimens (3 mm) were lesioned in demineralizing solution for 96 h and were then divided into three groups. One group was autoclaved; one group was gas sterilized (ethylene oxide), and the remaining 24 specimens were further disinfected in 70% ethanol for 10 min. Specimens in each group were then treated 4 times/day for 4 weeks with 0, 250 or 1,100 ppm F dentifrice slurries in an in vitro cycling, remin/demin model. Following treatment, fluoride uptake was analyzed by microdrill biopsy, and lesion depth and mineral content changes (DeltaM) were determined by transverse microradiography. Data were analyzed by one-way ANOVA analysis. In all three groups of specimens there were significant (p<0.05) differences in fluoride uptake in response to different fluoride treatments. Autoclaved lesions failed to provide dose- response data with regard to changes in lesion mineral content. Because formalin and 70% alcohol are only disinfectants, and autoclaving altered the responsiveness of enamel lesions, results from this study suggest that, of the methods tested, gas sterilization is the preferred method for sterilizing enamel specimens that will be used in intra-oral studies.