With the at-home system, you will be provided with plastic trays moulded to the shape of your teeth. A small amount of whitening gel is placed in the trays and the trays are then placed in your mouth for up to an hour a day. The at-home system usually takes between two and three weeks to achieve a good result.
You can always purchase more gel for 'topping up' the procedure in the future as you feel necessary.
Sensitivity can occur during whitening, but can usually be managed by stopping use of the gel for a day or two, or by using a desensitising paste.