Sensodyne Rapid Action contains strontium which acts to create a mineral-like seal over the surface of the dentine and within the microscopic channels. This prevents stimulus from reaching the nerve. Twice daily brushing provides long lasting protection from sensitivity. Also the fluoride helps to protect and strengthen teeth.Sensodyne fast action provides relief from tooth pain sensitivity within 60 seconds with twice daily brushing. When used in accordance with the guidelines / directives individual results may vary