title: Effects of bleaching agents on human enamel light reflectance.
abstract: OBJECTIVE
  Tooth whitening has been associated with splitting-up chromogenic molecules by hydrogen peroxides. Though micromorphological alterations are well documented, little is known about optical changes as a function of shifting in wavelengths. Therefore, the aim of the current study was to measure reflectance changes after bleaching in vitro by using a spectrometer.
  
  
  METHODS
  Forty-eight enamel slabs (diameter = 5 mm) were prepared from the sound enamel of extracted human teeth that were: 1) fully impacted, 2) from juveniles ages 10 to 16 years, 3) from adults 35 to 45 years of age and 4) from seniors older than age 65. In all specimens, the baseline total reflectance measurement was performed with a computer-assisted spectrometer (Ocean Optics, Dunedin, FL, USA) within wavelengths (wl) from 430 nm to 800 nm. Four enamel samples of each age group were exposed to either 10% or 15% carbamide peroxide (Illuminé Home, Dentsply, Konstanz, Germany) or 35% hydrogen peroxide (Pola Office, SDI Limited, Victoria, Australia). After surface treatment, all slabs underwent total reflectance measurement again. Statistical analysis was calculated at wl 450, 500 and 750 nm using the Student's paired t-test and one-way variance analysis.
  
  
  RESULTS
  Total reflectance significantly increased after bleaching at all enamel maturation stages, irrespective of the bleaching agent concentration, for wl 450 nm (blue) and 500 nm (green) with p<0.0001. At 750 nm (red), significant changes only occurred in enamel from adults and seniors (p<0.04). However, the efficacy of bleaching was significantly increased in the blue and green light spectra as compared to the red spectra (p<0.0001).
  
  
  CONCLUSIONS
  The results of the current study showed that the exclusive assumption of the "chromophore effect" in dental bleaching could not be sustained, because whitening of the dental enamel works at different maturation stages, even in impacted teeth. This effect is irrespective of the bleaching protocol used and the bleaching agent concentration.
authors.affiliation: University of Witten/Herdecke, Operative and Preventive Dentistry, Witten, Germany. Ljubisa.Markovic@uni-wh.de
authors.forename: Ljubisa
authors.initials: L
authors.lastname: Markovic
authors.forename: Kasra
authors.initials: K
authors.lastname: Fotouhi
authors.forename: Heribert
authors.initials: H
authors.lastname: Lorenz
authors.forename: Rainer A
authors.initials: RA
authors.lastname: Jordan
authors.forename: Peter
authors.initials: P
authors.lastname: Gaengler
authors.forename: Stefan
authors.initials: S
authors.lastname: Zimmer
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000077463:Carbamide Peroxide; D002648:Child; D003743:Dental Enamel / Q000033:anatomy & histology / Q000187:drug effects*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008027:Light; D008875:Middle Aged; D055100:Optical Fibers; D016877:Oxidants / Q000494:pharmacology*; D010545:Peroxides / Q000494:pharmacology; D013053:Spectrophotometry; D014073:Tooth Bleaching / Q000379:methods*; D014095:Tooth, Impacted / Q000473:pathology; D014508:Urea / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D016877:Oxidants; D010545:Peroxides; D000077463:Carbamide Peroxide; D014508:Urea; D006861:Hydrogen Peroxide