Key factors influencing outcome of peroxide-based bleaching treatments in dentistry
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The efficacy and safety of peroxide-based teeth whitening has been a largely contested issue over the last two decades. Several reviews have been written on the subject, but the current literature lacks a more involved description of the key factors that influence whitening effects and the manifestation of its adverse effects. Thus, a review of these key factors should be able to more clearly define how these influence treatment outcome during peroxide-based teeth whitening treatments, and how these treatments are likely to expose individuals to additional risk factors. Based on evidence in the current literature, whitening efficacies are dependent on a series of variables associated with treatment. Of these variables, the ones more directly associated with the whitening effects produced after treatment are peroxide concentration, active bleaching time, and--to some extent--the choice between currently available delivery systems (trays, strips, application brushes). From the studies reviewed, higher concentrations of peroxide produce more pronounced whitening effects, while lower concentrations needing longer active bleaching times to produce similar color changes, as measured by either VITA shade guides, or the CIEL*a*b* system. Color relegations are likely to occur with treatments composed of lower number of treatment sessions compared to treatments with multiple sessions. In terms of adverse effects, peroxides have been found to potentially be associated with carcinogenicity and cytotoxicity not only in oral tissues but in the gastrointestinal lining of hamsters and rats during in vivo studies. However, current reviews and studies have highlighted that excessive levels of peroxide exposure are needed to promote tumor growth or induce cytotoxic effects in the oral cavity; thus, it is unlikely that teeth whitening use of peroxides exposes individuals to dangerous levels of carcinogenicity and cytotoxicity. Nevertheless, some studies have found a decrease in odontoblast viability at concentrations of 16% carbamide peroxide, suggesting cytotoxicity may become a more significant factor at carbamide peroxide concentrations higher than 16%. Tooth and gingival sensitivity was closely associated with the use of either higher peroxide concentrations or longer active bleaching times. However, desensitizing agents such as fluoride, potassium nitrate, and amorphous calcium-phosphate have been found to effectively reduce this sensitivity of teeth and gingival tissues in people experiencing tissue sensitivity. Structural damage to enamel and dentin were found to be statistically insignificant in the studies reviewed, with whitening products of low acidity causing the bulk of the observed demineralization in in vitro studies. In vivo studies evaluating peroxide-associated demineralization have suggested that salivary components are capable of fully remineralizing any affected teeth structures following peroxide-based teeth whitening. In conclusion, from the studies analyzed, it is advisable to use concentrations lower than 16% carbamide peroxide during at-home treatments. However, use of higher concentrations are acceptable if provided under professional supervision. People with gingival recessions are more likely to experience sensitivity, so use of desensitizing agents at the time of treatment is advisable. In terms of whitening pastes, whitening gels of relatively neutral pH should be used (pH between 5 and 7) to reduce enamel and dentin demineralization; additives may include desensitizing agents to help with sensitivity and antioxidants which can counteract the oxidative stress of peroxides on oral tissues.
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