title: Effect of 15% carbamide peroxide bleaching gel on color stability of giomer and microfilled composite resin: an in vitro comparison.
abstract: OBJECTIVE
  The effect of 15% carbamide peroxide bleaching gel on color stability and surface topography of a giomer and a microfilled composite resin was evaluated in the present in vitro study.
  
  
  METHODS
  Forty discs measuring 10 mm in diameter and 1 mm in thickness were prepared from a giomer and a microfilled composite resin. Each material yielded 20 discs with completely smooth surfaces. Then a spectrophotometer was used to measure L* (lightness), a* (redness, greenness) and b* (blueness, yellowness) color coordinates of all the discs. Subsequently, the specimens were subjected to 15% carbamide peroxide bleaching gel. After measuring the color coordinates once again, color changes (ΔE*) were calculated by the CIELAB system. Four specimens from each material (two specimens before bleaching agent application and two specimens thereafter) were viewed under an atomic force microscope (AFM) for surface topography evaluation. Data were analyzed by Mann-Whitney U and Kruskal-Wallis tests at α=0.05.
  
  
  RESULTS
  There were no statistically significant differences in color changes (ΔE*) between the two materials (P>0.05). In addition, no significant differences were detected in surface roughness between composite resin and giomer discs before and after bleaching (P>0.05 for both). However, in both materials the differences in surface roughness were significant before and after bleaching procedures (P<0.001).
  
  
  CONCLUSIONS
  Based on the results of the present study it was concluded that 15% carbamide peroxide does not induce clinically detectable color changes in composite resin and giomer despite an increase in surface roughness.
authors.affiliation: Department of Operative Dentistry, School of Dentistry, Tabriz University of Medical Sciences, Tabriz, Iran.
authors.forename: Narmin
authors.initials: N
authors.lastname: Mohammadi
authors.forename: Soodabeh
authors.initials: S
authors.lastname: Kimyai
authors.forename: Mehdi
authors.initials: M
authors.lastname: Abed-Kahnamoii
authors.forename: Mohammad-Esmaeel
authors.initials: ME
authors.lastname: Ebrahimi-Chaharom
authors.forename: Alireza
authors.initials: A
authors.lastname: Sadr
authors.forename: Mehdi
authors.initials: M
authors.lastname: Daneshi
mesh_terms: D000077463:Carbamide Peroxide; D003116:Color; D003188:Composite Resins; D003793:Dental Restoration, Permanent; D005782:Gels; D008422:Materials Testing; D010545:Peroxides / Q000008:administration & dosage*; D058205:Tooth Bleaching Agents / Q000008:administration & dosage*; D014508:Urea / Q000008:administration & dosage / Q000031:analogs & derivatives*
chemical_list: D003188:Composite Resins; D005782:Gels; D010545:Peroxides; D058205:Tooth Bleaching Agents; D000077463:Carbamide Peroxide; D014508:Urea