In-vitro Evaluation of Mechanism and Performance of Antisensitivity Dentifrices

Objectives: This in vitro study was designed to improve understanding of the relative performance and mechanism of action of two common OTC antisensitivity therapies, i.e. KNO₃- and bioavailable SnF₂-based dentifrice.
Methods: Sections of etched coronal human dentin were mounted in a Pashley-type liquid cell with a novel open-faced design to permit brushing of the dentin surface. Reduction in hydrodynamic flow through coronal human dentin was observed following 60 s “slurry-in-place” applications of a bioavailable stannous fluoride antisensitivity dentifrice (BSFD), a cavity protection (CCP) control dentifrice, and a potassium nitrate-containing dentifrice (KNO3). In addition, potassium flux through dentin was measured as a function of hydrodynamic flow.
Results: All dentifrices significantly reduced hydrodynamic flow in etched dentin. Rank order of mean flow reductions (± standard deviation) following 12 successive applications were 67.8% (±10.2%), 53.0% (±13.5%), and 42.9% (±5.5%) for BSFD, KNO3, and CCP dentifrices, respectively. For the final flow measurement, mean differences were statistically-significant for only control and BSFD products with a 2-tailed p-value of <0.05. However, least-squares regression of the plateau region in application vs. flow data (cycles 7+) demonstrated that all intercepts were statistically different. Although partial occlusion enhanced potassium permeation, the cumulative flux did not appear sufficient to significantly raise pulpal potassium concentration above background levels.
Conclusions: Flow reduction, commonly associated with sensitivity relief, was significant and different for all dentifrices tested, including those not labeled for sensitivity relief. While more studies are needed, this work suggests that occlusion is at least partially responsible for the modest clinical benefits observed with KNO₃-based dentifrice. This hypothesis appears to be more consistent with the timeframe reported for onset of clinical relief with KNO₃-based dentifrice than that of potassium diffusion. Not surprisingly, application of the bioavailable SnF₂ dentifrice, which is designed and intended to occlude, produced significantly greater in vitro flow reduction.