title: Effects of the bleaching procedures on enamel micro-hardness: Plasma Arc and diode laser comparison.
abstract: OBJECTIVE
  One of the major side effects of vital bleaching is the reduction of enamel micro-hardness. The purpose of this study was to evaluate the influence of two different bleaching systems, Plasma Arc and GaAlAs laser, on the enamel micro-hardness.
  
  
  METHODS
  15 freshly extracted human third molars were sectioned to prepare 30 enamel blocks (5×5 mm). These samples were then randomly divided into 2 groups of 15 each (n=15): a plasma arc bleaching group (: 350-700 nm) + 35% Hydrogen Peroxide whitening gel and a laser bleaching group (GaAlAs laser, λ: 810 nm, P: 10 W, CW, Special Tip) + 35% Hydrogen Peroxide whitening gel. Samples were subjected to the Vickers micro-hardness test (VHN) at a load of 50 g for 15s before and after treatment. Data were statistically analyzed by a Mann-Whitney test (p≤0.05).
  
  
  RESULTS
  In the GaAlAs laser group, the enamel micro-hardness was 618.2 before and was reduced to 544.6 after bleaching procedures. In the plasma arc group, the enamel micro-hardness was 644.8 before and 498.9 after bleaching. Although both techniques significantly reduced VHN, plasma arc bleaching resulted in a 22.62% reduction in VHN for enamel micro-hardness, whereas an 11.89% reduction in VHN was observed for laser bleaching; this difference is statistically significant (p<0.001).
  
  
  CONCLUSIONS
  Both bleaching techniques reduced enamel micro-hardness, although the reduction is much less significant with the GaAlAs laser than with the plasma arc. Therefore GaAlAs laser bleaching has fewer harmful effects than plasma arc in respect to enamel micro-hardness reduction.
authors.affiliation: Department of Operative Dentistry. Dental School.Islamic Azad University of Medical Sciences. Tehran.
authors.forename: Saeid
authors.initials: S
authors.lastname: Nematianaraki
authors.affiliation: Laser Research Center in Medical Sciences (LRCMS), AJA University of medical Sciences. Tehran.
authors.forename: Reza
authors.initials: R
authors.lastname: Fekrazad
authors.affiliation: Department of Operative Dentistry. Dental School.Islamic Azad University of Medical Sciences. Tehran.
authors.forename: Nasim
authors.initials: N
authors.lastname: Naghibi
authors.affiliation: Iranian Medical Laser Association.
authors.forename: Katayoun Am
authors.initials: KA
authors.lastname: Kalhori
authors.affiliation: Camilo Castelo Branco University, São Jose dos Campos, SP.
authors.forename: Aldo Brugnera
authors.initials: AB
authors.lastname: Junior
keywords: Bleaching; GaAlAs Laser; micro-hardness; plasma arc