All bleaching methods have the potential to cause some side effects, although not all patients will experience them. The most commonly reported side effects are increased tooth sensitivity and gingival irritation.1,3,8,9,13,24,25 Side effects tend to be short lived, clearing up after bleaching is stopped. Effects of bleaching have been studied for 30 years and there have been no long-term systemic or oral health issues discovered.3
Tooth Sensitivity: Patients should be advised that tooth sensitivity is a common side effect of the tooth bleaching process. It can happen early in the process, therefore, taking steps to minimise potential sensitivity before it starts will benefit the patient as it is always better to prevent than treat after the fact. Sensitivity may occur if the flow of fluid within dentinal tubules increases. When tubules are occluded, e.g., by smear plugs, there is less flow of fluid. However, during the bleaching process oxygenation occurs, which results in the removal of smear plugs. Consequently, transient sensitivity may occur for some.
Whether one experiences sensitivity depends on different factors such as: concentration of the bleaching agent, contact time of bleach on the tooth, frequency of bleaching, and an individual’s susceptibility to sensitivity/history of sensitive teeth.1,3,8,24 Although systematic reviews/meta-analysis have not shown significant differences in tooth sensitivity comparing in-office and at-home techniques, lower concentrations (10% CP) are typically favoured when looking to minimise risk for patients.14,21,24 Recommending the application of an in-office desensitising agent, such as fluoride varnish, before treatment and/or a toothpaste containing stannous fluoride or potassium nitrate starting two weeks before bleaching can help minimise sensitivity.25
Gingival Irritation: If HP has access to the gingival tissue, it can cause mucosal irritation. This can appear as a white mark or burn on the tissue. Gingival irritation most commonly occurs with at-home bleaching when custom trays or OTC trays are ill-fitted, excess HP gel is dispensed into trays, or if an individual wears the trays longer than stated in the directions.4,25 The uniform unit-dose on a whitening strip may help prevent dispensing excess gel and its direct contact with the tooth surface may minimise contact with the gingival tissue. When high concentrations of HP are used, as with in-office bleaching, measures to cover and protect the gingival tissue must be taken to ensure the bleach causes no harm.25
Other Side Effects: There have been occasional reports of headaches, TMJ pain, sore throats, gastric pain, tooth erosion, pulpal damage, and increased susceptibility to demineralisation associated with tooth bleaching.1,8,9,25 The integrity of dental restorative material after bleaching has been studied in vitro showing the possibility of negative influence.3,9