Risks

Side effects of teeth bleaching include:

* Chemical burns from gel bleaching (if a high-concentration oxidizing agent contacts unprotected tissues, which may bleach or discolor mucous membranes), sensitive teeth
* Overbleaching (known in the profession as "over-white teeth") aka "Hyperodonto-oxidation"
* Rebound, or teeth losing the bleached effect, particularly with the intensive treatments (products that provide a large change in tooth colour over a very short treatment period, e.g., 1 hour)

A recent study by Kugel et al. showed that nearly half the initial change in color provided by an intensive in-office treatment (i.e., 1 hour treatment in a dentist's chair) may be lost in seven days.[10] Rebound is experienced when a large proportion of the tooth whitening has come from tooth dehydration (also a significant factor in causing sensitivity).[11] As the tooth rehydrates, tooth color 'rebounds' back toward where it started.[12]

Home tooth bleaching treatments can very slightly reduce tooth enamel.[13] There have been long term Tetracycline studies done where patients received high concentration bleach, over night, for 6 months. These studies show that even over long term exposure, the amount of reduction in tooth enamel is insignificant.

The side effects that occur most often are a temporary increase in tooth sensitivity and mild irritation of the soft tissues of the mouth, particularly the gums.[14] Tooth sensitivity often occurs during early stages of the bleaching treatment. Tissue irritation most commonly results from an ill-fitting mouthpiece tray rather than the tooth-bleaching agent. Both of these conditions usually are temporary and disappear within 1 to 3 days of stopping or completing treatment.

Individuals with sensitive teeth and gums, receding gums and/or defective restorations should consult with their dentist prior to using a tooth whitening system. People who are sensitive to hydrogen peroxide (the whitening agent) should not try a bleaching product without first consulting a dentist. Also, prolonged exposure to bleaching agents may damage tooth enamel. This is especially the case with home remedy whitening products that contain fruit acids.

Bleaching is not recommended in children under the age of 16. This is because the pulp chamber, or nerve of the tooth, is enlarged until this age. Tooth whitening under this condition could irritate the pulp or cause it to become sensitive. Tooth whitening is also not recommended in pregnant or lactating women.

Tooth whitening does not usually change the color of fillings and other restorative materials. It does not affect porcelain, other ceramics, or dental gold. However, it can slightly affect restorations made with composite materials, cements and dental amalgams. Tooth whitening can restore color of fillings, porcelain, and other ceramics when they become stained by foods, drinks, and smoking, among other activities.[citation needed]

Although some over-the-counter bleaching products contain carbamide peroxide, most of them are H2O2 based, which has the potential to interact with DNA. Therefore, there is some concern with H2O2 carcinogenicity and non-carcinogenicity. However, there is no sufficient research in this sense. What the studies have been able to show is that H2O2 is both an irritant and cytotoxic. Clinical studies have found a higher occurrence of gingival irritation when patients use bleaching materials with higher peroxide concentrations.