Influence of study design on the impact of bleaching agents on dental enamel microhardness: A review

Abstract

OBJECTIVE: Numerous studies investigated the impact of bleaching procedures on enamel microhardness. The outcomes of these studies reveal inconsistencies regarding the fact whether a microhardness reduction due to bleaching occurs or not. Aim of the present review was to summarize the existing literature of external bleaching therapies, which used microhardness tests for evaluation of possible effects on enamel and to weigh up different parameters of the study designs with respect to the outcome of these studies. METHODS: The data from original scientific full papers listed in PubMed or ISI Web of Science (search term: enamel and (bleaching or peroxide) and (hardness or microhardness or Knoop or Vickers)) and received by additional hand-search meeting the inclusion criteria were included in the review. Influences of different parameters on the outcome of the bleaching treatments were analyzed with the Fisher's-exact-test. RESULTS: A total of 55 studies were identified with 166 hardness measurements conducted directly after bleaching and 69 measurements performed after a post-treatment episode. Directly after bleaching, 84 (51%) treatments showed microhardness reduction compared to baseline, whereas 82 (49%) did not yield microhardness reduction. After the post-treatment episode, 20 (29%) treatments showed hardness reduction and 49 (71%) did not. A significant higher number of bleaching treatments resulting in enamel microhardness reduction were observed, when artificial instead of human saliva was used for storage of the enamel samples in the intervals between the bleaching applications and when no fluoridation measures were applied during or after the bleaching phase. SIGNIFICANCE: The review shows that in those studies, which simulated the intraoral conditions as closely as possible, the risk of enamel microhardness decrease due to bleaching treatments seems to be reduced. Nevertheless more in situ-and in vivo-studies are needed to verify this observation. 1Influence of study design on the impact of bleaching agents on dental enamel Conclusion: The review shows that in those studies, which simulated the intraoral conditions as closely as possible, the risk of enamel microhardness decrease due to bleaching treatments seems to be reduced. Nevertheless more in-situ-and in-vivo-studies are needed to verify this observation.3

Effectiveness of nano-calcium phosphate paste on sensitivity during and after bleaching: a randomized clinical trial

“…21,22 It appears that these small changes in the enamel produced by bleaching did not seem to be a problem as they were resolved by the remineralizing action of saliva. 23 This explains why previous application of fluoride before bleaching was not capable of reducing the bleaching-induced tooth sensitivity. 10 In addition to fluoride, the desensitizing paste used contained a nano-calcium phosphate compound which is believed to minimize reduction in enamel microhardness after bleaching by depositing calcium phosphate on the enamel surface, producing remineralization.…”

In situ Effect of Nanohydroxyapatite Paste in Enamel Teeth Bleaching

“…16,37 Because it contains manometric particles, nano-HAP is able to penetrate these erosion areas to avoid further demineralization and promote remineralization with the deposition of: 38,39 Ca PO OH The chemical and biological characteristics of the nano-HAP described above may justify the increase of the F ions percentage when compared with the other groups analyzed, and the lower loss of Ca and P ions in relation to the group just cleared. …”

“…The oral cavity presents several factors that may minimize the deleterious effects caused by the bleaching treatment, 14,15 including the presence of saliva, 14 which suggests reversing the changes related to whitening. 16 Saliva has the ability to buffer, due to bicarbonate, and the phosphate system of inorganic electrolytes, such as phosphorus, calcium, and fluoride and the presence of enzymes and bacteria. 17 A qualitative analytical study indicated a significant reduction in the calcium content, phosphate, and fluoride in the enamel after bleaching with HP in both low and high concentrations.…”

Fracture Resistance of Endodontically-treated Teeth: Effect of Combination Bleaching and an Antioxidant

“…31 Some studies have reported that bleaching leads to the removal of calcium, phosphate and other ions from dental structures. [30][31] The authors assumed that, in this case, compared with unbleached dental tissues, the penetration of antioxidant is facilitated and thus, considering the adhesion promotion capacity of antioxidant, a stronger resin-tooth interlocking is obtained. This finding is consistent with the results of a recent study by Turkan and others.…”