title: Effect of bleaching agents on the microhardness of tooth-colored restorative materials.
abstract: BACKGROUND
  There is no consensus concerning the effect of bleaching gels on microhardness of restorative materials. Information about the effect of whitening strips on microhardness of restorative materials is also limited.
  
  
  OBJECTIVE
  The purpose of this study was to evaluate the effect of a bleaching gel and a whitening strip on the microhardness of 3 tooth-colored restorative materials.
  
  
  METHODS
  Forty cylindrical specimens (6 x 2 mm) of each restorative material, including a nanohybrid composite resin (Grandio), a polyacid-modified composite resin (Dyract eXtra), and a glass-ionomer cement (Ionofil Molar AC), were prepared and stored in distilled water at 37 degrees C for 24 hours. The specimens were then polished using medium, fine, and superfine polishing disks and stored in 37 degrees C distilled water for 7 days. Specimens were divided into 4 groups (n=10). One group was selected for baseline Vickers hardness measurements (load 100 g, dwell time 20 seconds) of the top surfaces. The other 3 groups were treated for 21 days with 1 of the following: distilled water (control), bleaching gel (10% carbamide peroxide), or whitening strip (14% hydrogen peroxide). The top surfaces of the treated specimens were also subjected to the same hardness testing performed for the baseline specimens. Data were analyzed with 2-way analysis of variance and Tukey Honestly Significant Difference tests (alpha=.05).
  
  
  RESULTS
  There were no significant differences in microhardness between the test groups of each restorative material. However, significant differences in microhardness were observed among restorative materials. For all test groups, composite resin showed the highest hardness values, whereas glass-ionomer cement presented the lowest (P<.05).
  
  
  CONCLUSIONS
  The bleaching products used in this study did not adversely affect the microhardness of the restorative materials.
authors.affiliation: Department of Operative Dentistry, Faculty of Dentistry, Ankara University, Ankara, Turkey. mujdeci@dentistry.ankara.edu.tr
authors.forename: Arzu
authors.initials: A
authors.lastname: Mujdeci
authors.forename: Osman
authors.initials: O
authors.lastname: Gokay
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D000704:Analysis of Variance; D000077463:Carbamide Peroxide; D020770:Compomers / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D004338:Drug Combinations; D005899:Glass Ionomer Cements / Q000737:chemistry; D006244:Hardness / Q000187:drug effects; D006245:Hardness Tests / Q000379:methods; D006861:Hydrogen Peroxide / Q000009:adverse effects*; D010545:Peroxides / Q000009:adverse effects*; D011140:Polyurethanes / Q000737:chemistry; D014073:Tooth Bleaching / Q000009:adverse effects*; D014508:Urea / Q000009:adverse effects / Q000031:analogs & derivatives*
chemical_list: D000180:Acrylic Resins; D020770:Compomers; C029012:Composite Dental Resin; D003188:Composite Resins; D004338:Drug Combinations; D005899:Glass Ionomer Cements; D010545:Peroxides; D011140:Polyurethanes; D000077463:Carbamide Peroxide; D014508:Urea; D006861:Hydrogen Peroxide