Tooth sensitivity occurs when the dentine underneath tooth enamel becomes exposed. When exposed dentine comes into contact with hot or cold, sweet, sour or even your toothbrush, it can trigger the nerve, causing a short sharp pain. Sensodyne Repair & Protect Extra Fresh contains Novamin is different from other toothpastes. It has a unique, clinically proven concentrated calcium formula that helps repair vulnerable areas with the natural building blocks of your teeth, whilst its Extra Fresh flavour leaves your mouth feeling fresh and clean. NOVAMIN formula releases the building blocks of teeth: calcium and phosphate. These ions form a protective mineral layer to repair the vulnerable areas of the tooth.