Fluoride Dose-response of a Modified In situ caries Model

Objectives: Evaluate the fluoride (F) dose-response of 0/250/500/1100 ppm F of our standard in situ model (SM) involving human enamel specimens with a modified model (MM) involving bovine enamel specimens.
Methods: In this single-center, randomized, double-blind, four-way-crossover-design in situ study, healthy subjects (n=27) wore intra-oral partial denture appliances containing four gauze-covered partially-demineralized enamel specimens: two 4×4 mm human enamel specimens placed in the subject’s partial denture buccal flange area (SM); two 4 mm round bovine enamel specimens placed in a denture tooth location on the same side of the partial denture (MM). Subjects applied their assigned dentifrice by brushing for 1 min 2 x day: NaF/silica/toothpaste with either 0 ppm F, 250 ppm F (dose-response control), 500 ppm F (dose-response control), or 1100 ppm F (positive control). Enamel specimens were removed after 14-day intra-oral exposure. Outcome measures assessed were: % surface microhardness recovery (%SMHR), net acid resistance (NAR), comparative acid resistance (CAR), enamel fluoride uptake (EFU), transverse microradiography (TMR Delta Z; TMR L).
Results: Nothing was statistically significant for the MM vs SM comparisons. Models were equivalent for TMR L (any F level), TMR Delta Z at 250 ppm F, %SMHR, NAR and CAR (0 and 250 ppm F). MM performed in a similar manner to SM for the key outcome measures (%SMHR and EFU) and in general appears to have greater sensitivity to distinguish the effects of F for all outcome measures.
Conclusions: The modified model with bovine enamel placed in denture teeth performed in a similar manner to the standard model with human teeth placed in the buccal flange, and thus is suitable for future in situ studies comparing dentifrice product treatments.