title: Effects of a bleaching agent with calcium on bovine enamel.
abstract: OBJECTIVE
  This in vitro study analyzed the effects of a bleaching treatment containing 35% hydrogen peroxide (HP) with or without calcium on bovine enamel, using the Knoop hardness number (KHN), tristimulus colorimetry (TC), and scanning electron microscopy.
  
  
  METHODS
  Forty-five specimens were randomly divided into groups (n = 5), which included artificial saliva (negative control [NC]), 35% HP (positive control [PC]), and 35% HP Blue Calcium (HP Blue). The specimens were subjected to three bleaching sessions. During the sessions, the specimens were immersed in artificial saliva at 37°C. Before and after bleaching, KHN tests were conducted using a force of 25 gf for 5 s. TC was performed using the CIE-L*a*b* system and readouts were obtained at the following 4 time points: Before the bleaching treatment; after the first session, the second session, and the third session. The specimens were dehydrated and coated with gold, and the photomicrographs were analyzed in a double-blind manner with a LEO microscope.
  
  
  RESULTS
  Using one-way analysis of variance and Tukey's test (P < 0.05), a statistically significant difference was identified between the initial and final mean KHNs of the NC and PC groups, while the initial and final mean KHNs were not significantly different in the HP Blue group. The final mean values of ΔE, ΔL, and Δb of the PC and HP Blue groups were significantly higher than the initial values (P < 0.01 for both). The photomicrographs revealed no differences among the groups.
  
  
  CONCLUSIONS
  Therefore, treatment with HP Blue prevented changes in the KHN without reducing the efficacy of bleaching.
authors.affiliation: Department of Restorative Dentistry, Federal University of Pará, Belem, Para, Brazil.
authors.forename: Larissa
authors.initials: L
authors.lastname: Alexandrino
authors.affiliation: Department of Restorative Dentistry, Federal University of Pará, Belem, Para, Brazil.
authors.forename: Yasmin
authors.initials: Y
authors.lastname: Gomes
authors.affiliation: Department of Restorative Dentistry, Federal University of Pará, Belem, Para, Brazil.
authors.forename: Eliane
authors.initials: E
authors.lastname: Alves
authors.affiliation: Laboratory of Electron Microscopy, Museum Emilio Goeldi, Belem, Para, Brazil.
authors.forename: Hilton
authors.initials: H
authors.lastname: Costi
authors.affiliation: Department of Food Engineering, Federal University of Pará, and Centre for Agro-food Valorization of Amazonian Bioactive Compounds, Belem, Para, Brazil.
authors.forename: Hervé
authors.initials: H
authors.lastname: Rogez
authors.affiliation: Department of Restorative Dentistry, Federal University of Pará, Belem, Para, Brazil.
authors.forename: Cecy
authors.initials: C
authors.lastname: Silva
keywords: Color; hydrogen peroxide; microhardness; scanning electron microscopy