A pH Cycling Model as an Alternate to Animal Testing under the FDA Anticaries Monograph

Objective: Seven pH cycling studies were conducted to establish the fluoride dose response for comparison with dose response data from our animal caries database. Methods: Sterilized, caries-free, human crowns of molars and pre-molars were cleaned and polished with a 5µm alumina slurry. Crowns were painted with nail varnish leaving one small window of enamel exposed. The windows were exposed to test slurries at all times during the treatments and subsequent incubations in de- and remineralizing solutions. The treatments and incubations in de/remineralization solutions (referred to as pH cycling) were repeated daily for a total of 14 days. Specimens were treated with dentifrice slurries for one minute, placed into demineralizing solution for 6 hours, treated with dentifrice slurries for one minute again, and then placed in remineralizing solution for 16 hours. Specimens were evaluated using a cross-sectional microhardness technique and reported as Delta Z (lesion severity, micrometers x vol% mineral). Results: The treatment groups compared were a) 1100ppm F, b) 250ppm F and c) <1ppm F (placebo). The mean Delta Z values (± stdev) for the series were a) 945 ± 302, b) 2238 ± 873 and c) 4291 ±1181, with a>b>c performance (significant @ p=0.05). These results were compared to results observed in three previous animal caries studies where mean caries scores were a) 21 ± 4, b) 30 ± 3 and c) 36 ± 5. Good agreement was observed indicating the two models have similar capability of separating treatments based on concentration of available fluoride and thus similar capability for discriminating against potentially inferior dentifrice products with lower levels of available fluoride. Conclusion: Based on the variances and response to fluoride dose, we conclude that this pH cycling model may provide equivalent accuracy to the animal caries model when evaluating NaF and SnF₂based formulations under the Anticaries Monograph.