This two-phase experiment assessed the effects over time of a solution containing 1.09% sodium fluoride, .40% stannous fluoride, and .14% hydrogen fluoride (.717% fluoride solution, DentinBloc) on pain associated with dentinal hypersensitivity. During phase I, 30 subjects demonstrating dentinal hypersensitivity to a blast of cool air were divided into three double blind experimental groups. After baseline data were collected for all subjects, one group was instructed to apply the .717% fluoride solution twice a day. A second group was instructed to apply a gel containing .04% stannous fluoride (Gel-Kam) twice a day. A third group was instructed to apply distilled water. Each subject was assessed at 2, 4, 8, and 16 weeks utilizing the "method of limits" with a standardized, repeatable cold thermal stimulus. The results of a two factor repeated ANOVA indicated that those subjects who applied the .717% fluoride solution reported significantly less sensitivity at the 2-week period than the other groups (P < .05). In addition, those subjects whose solution contained the 0.4% stannous fluoride reported significantly less sensitivity at the 4- to 8-week periods (P < .05). Phase II of the study assessed the .717% fluoride solution on a more precise time course. These included: immediately, 15 minute, 1 day, 1 week and 2 weeks. A one factor repeated ANOVA revealed that this effect presented 15-minute post application (P < .05) and continued throughout the testing periods. It was concluded that the fully active 0.717% fluoride solution was an effective agent in the control of dentinal hypersensitivity after two 1-minute applications.