Effects of temperature and in-office bleaching agents on surface and subsurface properties of aesthetic restorative materials

Objectives: To investigate the effects of in-office bleaching agents on surface and subsurface properties of dental materials at different environmental temperatures. Methods: Four composite resins, a compomer, a conventional glass-ionomer cement (CGIC), and an industrially sintered ceramic material were evaluated in the present study. Four groups of each material (n = 10) were treated: bleaching with 40% hydrogen peroxide at 25 degrees C and 37 degrees C, stored in artificial saliva at 25 degrees C and 37 degrees C. The specimens from bleaching groups were bleached for two sessions, each of two 20 min application, at respective temperatures. After bleaching, the surface and subsurface (0.1-0.5 mm) microhardness were evaluated using a Vickers microhardness tester. The substance loss was determined by surface profilometry. The data were statistically analyzed with ANOVA and the Tukey's post hoc test. Results: All materials were found to have surface softening after bleaching, and bleaching effects on surface micorhardness increased at 37 degrees C compared with 25 degrees C, except for the ceramic. After being bleached at 37 degrees C, the microhardness values of flowable composite resin significantly reduced at a depth of 0.1 mm compared with control specimen stored at 37 degrees C. No significant difference was found between the control and bleached specimens with respect to substance loss for any of the materials. Conclusion: The influence of environmental temperature on the in-office bleaching effects on surface and subsurface microhardness of dental materials was material-dependent. However, no substance loss was detected due to the tested bleaching regimen. Clinical significance: Environmental temperature should be considered when evaluating the possible bleaching effects on restorative materials. Moreover, dentists should be aware that there might be a need for polishing of restorative materials in clinical situations in which restorations are accidentally exposed to bleaching gels. (C) 2013 Elsevier Ltd. All rights reserved.