Before bleaching one’s teeth, they should have a thorough dental examination by their dentist. One would not want to place bleach over cavities. The bleaching process many times will cause the teeth to be sensitive, so placing bleach into a cavity could increase the sensitivity. Bleaching is also not recommended for children under 16 because their pulp chamber in the center of the teeth where the nerves reside are very large which could make for extremely sensitive teeth. The peroxide ion has been shown to give off oxygen free radicals which have been shown to cause tissue damage. That is something I would not want to take a chance with in a growing child. Other issues include the possibility of gum irritation. The bleaching solutions, especially at the higher concentrations, can be somewhat caustic, and can injure the gums. Most of the time, it is just a temporary reddening and discomfort. This can be reduced by cutting the bleaching time or by switching to a weaker concentration of the bleaching solution. Both sensitivity and gum irritation tend to go away when the bleaching is stopped.
Vital teeth bleaching is performed by placing a peroxide based solution on the tooth surface. Even though tooth enamel is extremely hard, it is somewhat porous which allows the bleaching solution to leach into the tooth. The solution can be either hydrogen peroxide or carbamide peroxide. Carbamide peroxide will turn into hydrogen peroxide when it comes in contact with water. Once the peroxide ion has permeated into the body of the enamel and dentin, it will oxidize the stains that are residing inside the tooth structure thus, effectively lightening the tooth color. Studies have not shown any harm done to the enamel. The peroxide ion has been shown to give of oxygen free radicals which has been implicated as being possibly carcinogenic. No study has shown this to be a problem with short term use of the solutions. However, I personally feel that one should use caution when selecting a “whitening” toothpaste to make certain that they do not contain peroxides. Since toothpastes are used daily for not only years, but decades, I don’t think that it is a good idea to find out after the fact that there was some harm being done.