This single-center, randomized, double-blind, three-period crossover in situ study evaluated the enamel remineralization potential and fluoride bioavailability of three dentifrices-one fluoride-free negative control, one positive control with 0.243% sodium fluoride, and one investigational dentifrice containing 0.243% sodium fluoride and 20% sodium bicarbonate. Healthy adult subjects wore a palatal acrylic appliance containing demineralized enamel specimens for three 9-day treatment periods, during which in vivo brushing/slurry exposure and ex vivo sucrose challenges were performed. Outcomes included percent surface microhardness recovery (%SMHR) and post-treatment enamel fluoride concentration.