if you suffer from daily sensitivity especially to cold you may have receeded gumline. this results in exposure of the root area which is normally covered by the gum tissue. the root area has dentin without any enamel covering it. the dentin has tubules that run from the surface directly to the nerve canal or the pulp chamber, and therefore it transmits pain very easily. inorder to get relief these dentinal tubules need to be plugged. over-the-counter products like sensodyne or Act floride rinse have been shown to plug these tubules- like a cork on a wine bottle. you need to allow 2-3 weeks for these products to build up on the root surface. once they do you will notice significant relief from the sensitivity you were experiencing.