Teeth whitening below this age may cause irritation of the pulp or could make it more sensitive. Similarly, pregnant women as well as lactating mothers should also not undergo this process. Moreover, people having sensitive teeth and gum problems, receding gums and problems or defects in restoration must opt for their dentist's advice before undergoing the process. Similarly, those having allergies to peroxide are also not recommended to undergo the bleaching process.
Diseases in gums and teeth and decaying enamel are also not suitable cases for teeth whitening. Any cavity in the tooth may cause the bleaching solutions to seep into the existing decay causing further irritation. Again, people having exposed tooth roots are also discouraged since these roots do not have enamel cover. Teeth containing any kind of filling like crowns, veneer, bonding and bridges can not be bleached. Doing so may result in uneven whitening and it is advisable to complete the whitening process two weeks before the fillings. While the yellowish stains can be whitened easily, brown, gray, bluish-gray and purple ones show less response to teeth whitening.
Moreover the result may also vary from person to person. Smokers must refrain from smoking during teeth whitening the process to get the best results. The desired color should be a shade whiter than the whites of an eye.