OBJECTIVE The objective of this 16-week, double-blind, randomized, switch-over design study was to compare the efficacy in reducing dentin hypersensitivity of a dentifrice containing 8.0% arginine, calcium carbonate, and 1450 ppm fluoride as sodium monofluorophosphate (Colgate Sensitive Pro-Relief [also marketed as elmex Sensitive Professional]) to a desensitizing dentifrice containing 8% strontium acetate and 1040 ppm fluoride as sodium fluoride (Sensodyne Rapid Relief) under relevant consumer usage conditions. METHODS Qualifying subjects from the San Francisco, CA, USA area, who presented two hypersensitive teeth with a tactile hypersensitivity score (Yeaple Probe) between 10 and 50 grams of force and an air blast hypersensitivity score of 2 or 3 (Schiff Cold Air Sensitivity Scale), participated in this two-phase double-blind study. Subjects were randomly assigned to one of two test groups. The first phase of the study consisted of twice-daily at-home brushing with the first assigned dentifrice for eight weeks. The second phase of the study consisted of switching product use to the second assigned dentifrice for a second eight-week period. Dentin hypersensitivity examinations, which comprised tactile and air blast hypersensitivity measures, as well as examinations of oral hard and soft tissues, were conducted at baseline, at the completion of the first study phase, and at two weeks and eight weeks of the second phase. RESULTS One-hundred and twenty-one subjects complied with the study protocol and completed the study. Study Phase I: Subjects who brushed twice daily for eight weeks with the arginine/calcium carbonate dentifrice experienced statistically significant improvements in mean tactile and air blast hypersensitivity scores (51.3% and 39.4%, respectively) relative to that experienced by subjects who brushed with the strontium acetate dentifrice. Study Phase II: Subjects who brushed with the arginine/calcium carbonate dentifrice for the first eight weeks of the study and then switched to brush with the strontium acetate dentifrice for the second eight weeks of the study, did not exhibit further improvements in mean tactile or mean air blast hypersensitivity scores after two and eight weeks of switch-over product use. However, subjects who brushed with the strontium acetate dentifrice for the first eight weeks of the study and then switched to brush with the arginine/calcium carbonate dentifrice exhibited statistically significant improvements in mean tactile and air blast hypersensitivity scores two weeks (35.2% and 29.9%, respectively) and eight weeks (40.3% and 35.3%, respectively) after product switch-over. Relative to the subjects who switched from twice-daily brushing with the arginine/calcium carbonate dentifrice to brush with the strontium acetate dentifrice, those who switched from brushing with the strontium acetate dentifrice to brush with the arginine/calcium carbonate dentifrice exhibited statistically significant improvements in mean tactile hypersensitivity scores (10.3%) and in mean air blast hypersensitivity scores (16.3%) eight weeks after product switch-over. CONCLUSIONS Eight weeks of brushing with Colgate Sensitive Pro-Relief(elmex Sensitive Professional) provides significant reductions in mean dentin hypersensitivity relative to the identical use of Sensodyne Rapid Relief. Additionally, the dentin hypersensitivity reductions achieved by twice-daily brushing with Sensodyne Rapid Relief are significantly improved by switching to twice-daily brushing with Colgate Sensitive Pro-Relief (elmex Sensitive Professional) for two and eight weeks. Further, the dentin hypersensitivity reductions achieved by twice-daily brushing with Colgate Sensitive Pro-Relief (elmex Sensitive Professional) are not improved by switching to twice-daily brushing with Sensodyne Rapid Relief for two or eight weeks. Eight weeks' use of Colgate Sensitive Pro-Relief (elmex Sensitive Professional), after having used Sensodyne Rapid Relief for an initial eight-week time period, provides statistically significant improvements in dentin hypersensitivity relative to eight weeks' use of the Sensodyne Rapid Relief.