Sensitivity is a very common side effect of any teeth whitening treatment. Although sensitivity will naturally resolve upon completion of the treatment, the symptoms of sensitivity can be improved by using Desensitising Gel. The gel, which contains a super-high concentration of Potassium Nitrate (the active ingredient in Sensodyne toothpaste), is applied to your teeth whitening trays before, and after whitening (as needed) and worn for between 1 and 4 hours or until sensitivity subsides. Each order contains 1 x syringe of 3ml Desensitising Gel.