Patients using placebo dentifrices in clinical trials usually show a significant decrease in dentin sensitivity over a 2- to 4-week period. If their sensitivity were due to hydrodynamic fluid movement, then the results suggest that there was a decrease in their dentin permeability. This hypothesis was tested in vitro by measuring the ease with which fluid could flow (i.e., hydraulic conductance) across dentin discs before and after brushing the discs with a variety of dentifrices, including most of the marketed densensitizing dentifrices. All dentifrices decreased the hydraulic conductance of dentin. An experimental dentifrice containing oxalate as the active ingredient was far more effective than any of the marketed dentifrices. The results tend to support the hypothesis that, at least part of the reduction in clinical sensitivity in patients with hypersensitive dentin is due to the abrasive action of the dentifrice.
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