This is the reason why those wanting immediate effects will go for the supervised services of the dentist. Design differences for the mouthpiece trays. The mouthpiece trays that are available for supervised whitening sessions are considered as more reliable as compared to the ones that are available over the counter. It is recommended by oral health practitioners that this should be used twice a day. And through continuous use of around two to four weeks, there will be changes in the color of the teeth. Right now there are advances in the technology that allows for the teeth to become whiter at a shorter period of time. The youthful glow and sparkle of young teeth will in time lost its sheen as the enamel starts developing tiny cracks that will eventually lose the crystalline rods in the tooth, thinning the enamel making the teeth more transparent and showing through the yellowish color of the dentin. Even discounting this natural aging of the teeth, eating habits, food choices, medication, lifestyles, health conditions and many other factors will develop the tiny cracks in the enamel allowing debris to accumulate between the spaces staining the teeth. Irritation Bleaching agents contain peroxides. Peroxides when it gets in contact with the soft tissues inside the mouth will often give a tingling sensation that may not be pleasant to about half of the patients undergoing teeth whitening. Peroxides also have a taste that may be unpleasant to some. In any case though the taste is very bearable and the tingling sensation may be ticklish but the feeling is always a cleaner mouth afterwards. Teeth whitening gels, strips, pens, gurgles and other treatments are generally designed for self help and the mix is generally very mild. This is not only done to avoid problems but to market the products most effectively. Highly successful products depend much on acceptability, endorsement by word of mouth and repeat sales. There are however some risks involved when doing teeth whitening at home as some teeth could be sensitive than others and gums could also be irritated that could cause degrees of discomfort. When whitening the teeth at home, it will always be recommended to use those that have low concentration of whitening agents.