Before you begin a laser teeth whitening procedure, you'll need to protect your tongue and gums against the laser. The laser, while very effective, is very hot, and it can damage the tissue in your mouth. It is meant to heat the teeth and the teeth only. So, your provider will, after spreading your lips and cheeks away from the teeth, cover your tongue and gums with Vaseline or some other petroleum jelly product. The laser can dry the mouth, as well, so this jelly will keep your mouth from drying out, and it will prevent the laser from burning the tissue.