Title The Effect of Bleaching Agents on the Microhardness of Resin Composite Dental Restorative Materials Is Not Clinically Significant
Clinical Question Does carbamide peroxide or hydrogen peroxide bleaching agents reduce the microhardness of existing composite restorations in dental patients?
Clinical Bottom Line Although some studies show varied results depending on the specific type of composite and bleaching material used, most research indicates that there is either no difference in microhardness after bleaching, or the difference is very minor and therefore not clinically significant.
Best Evidence  
PubMed ID Author / Year Patient Group Study type
(level of evidence)
16472855Polydorou/2007Assorted dental resin composites and ceramicsLab study
Key resultsIn the Polydorou study, a total of 2425 indentations were made for testing knoop hardness on four different composite materials after bleaching for 0, 15, 30, or 45 seconds with Opalescence Xtra boost (38% Hydrogen Peroxide) bleaching agent. None of these materials showed a statistically significant effect of the in-office bleaching agent on composite microhardness. “The differences in the microhardness values between the bleached and the control samples for the composites were not statistically significant (hybrid: p=0.264; flow: p=0.584; micro-hybrid: p=0.278; nano-hybrid: p=0.405).”
18294750Yu/200836 Chinese volunteersRandomized controlled trial
Key resultsThis study used an at-home bleaching gel consisting of 15% carbamide peroxide (CP). "According to the repeated measures ANOVA, bleaching with 15% CP did not produce any statistically significant effect on the surface microhardness of the composite resin (Filtek Z350: p = 0.851; Filtek P60: p = 0.088)." The two conventional composites in this study were Filtek Z350 and Filtek P60.
Evidence Search (("tooth bleaching"[MeSH Terms] OR ("tooth"[All Fields] AND "bleaching"[All Fields]) OR "tooth bleaching"[All Fields]) AND composite[All Fields] AND ("hardness"[MeSH Terms] OR "hardness"[All Fields]))
Comments on
The Evidence
Validity: In Polydorou, the sample size is adequate, and the bleaching agent used is considered a strong one reserved only for in-office use. Additionally, the time intervals used mimic clinical use. Polydorou tested an in-office bleaching system only. Yu used an at-home bleaching agent and similarly found no significant change in microhardness. The control group showed no significant difference in microhardness either. For all groups, the trial lasted 28 days and the time intervals were the same (measured each week).
Applicability With the increased emphasis on esthetics in modern-day culture, new bleaching agents are being introduced every year. This could pose a risk to previous restorations. At this time, the evidence indicates the change in microhardness due to bleaching is not significant enough to influence the longevity of composite restorations. Therefore, it is unneccessary to replace a composite restoration simply because a patient has a bleached tooth, as the composite will maintain sufficient strength to resist fracture.
Specialty (General Dentistry) (Restorative Dentistry)
Keywords Bleaching, composite resin, microhardness
ID# 3003
Date of submission 03/23/2016
E-mail ACRES@livemail.uthscsa.edu
Author Matthew Acres
Co-author(s) e-mail
Faculty mentor James Summitt, DDS, MS
Faculty mentor e-mail Summitt@uthscsa.edu
Basic Science Rationale
(Mechanisms that may account for and/or explain the clinical question, i.e. is the answer to the clinical question consistent with basic biological, physical and/or behavioral science principles, laws and research?)
None available
Comments and Evidence-Based Updates on the CAT
None available