5 In an extensive review based selleck inhibitor on original articles that investigated the action of bleaching gels on different material surfaces, Attin et al3 found that when composite resins are bleached, roughness can be a relevant tool to assess surface changes. Roughness seems to be more affected by bleaching than microhardness. However, when saliva is present, adverse consequences are reduced because it acts as a protective barrier. Mor et al,12 Steinberg et al13 and Ulukapi et al2 also demonstrated both the ability of saliva to remineralize enamel after bleaching and its fluoride benefits. In the present study, as saliva was not considered, we could assess the potential of bleaching gels without this interference. Bleaching can also alter the optical properties of composite resins, which depend on the composition of materials as well as on the bleaching agent.

6,23 Results of the present study confirm that the action of the bleaching gel is not due to their low pH because the tested products had basic pH. However, basic environment also can lead to chemical interactions in the oral scenario.24 In this case, one of the main speculations refers to the hydrolytic action caused by chemical solutions on the organic matrix of resin composites, which is composed of hydrophobic monomers and diluents.26,27 It is also noteworthy that specimens were stored in water during the challenge period, and so, specimens were stored under hydrolytic environment. There is evidence in the literature that demonstrates that water causes changes in the properties of restorative materials.

These changes mainly occur at the interface between the filler and organic matrix.26,27 Alterations in the molecular structure of the matrix are under evaluation, and studies are being performed to make the matrix more resistant to chemical and mechanical challenges.28 The inorganic content of resin composites however, offers resistance to bleaching. Form, amount and distribution of fillers are all aspects that determine the clinical performance of these restorative materials.28,29 Despite advances in the evolution of composites, no material yet exists that is totally resistant to erosion/corrosion. Recent studies have reported that the durability of resin-based materials can be assured by polishing the restorations after bleaching.30,31 An interesting reaction between bleaching gel and composite resins was reported by Cho et al.

32 According to the authors, fracture toughness, which is the measure of a material��s ability to resist crack propagation, is considered to be a reliable indicator of the ability of dental materials to resist failure under load. The results of the Cho32 study showed a significant increase in fracture toughness values in the nanofilled composites after bleaching treatments. Cho et al32 also showed that the initial maximal polymerization GSK-3 of the control groups of other composites resulted in no change in fracture toughness values after bleaching.