title: Evaluation of Hydroxyl Radical Diffusion and Acidified Thiourea as a Scavenger during Intracoronal Bleaching.
abstract: BACKGROUND
  The diffusion of hydroxyl radicals in intracoronal bleaching is associated with a risk of invasive cervical resorption. The use of acidified thiourea has been recommended as a scavenger of residual radicals generated during intracoronal bleaching. The aims of this study were to quantify hydroxyl radical diffusion to external root surfaces after intracoronal bleaching with commonly used materials and to evaluate the effect of using acidified thiourea with hydrogen peroxide (H2O2) on hydroxyl radical diffusion.
  
  
  METHODS
  Eighty-two human premolars were prepared, stained, root filled, and allocated to experimental and control groups as follows: group 1: sodium perborate (SP) and water (n = 21), group 2: H2O2 (n = 21), group 3: acidified thiourea and H2O2 (n = 21), group 4: neutral thiourea and H2O2 (n = 10), control group 1: negative control (water) (n = 10), and control group 2: positive control (SP and H2O2) (n = 10). Materials were placed into the pulp chamber, sealed, and placed in 5 mmol/L terephthalic acid at 37°C for 48 hours. Hydroxyl radicals were quantified using a fluorescence microplate reader and high-performance liquid chromatography with fluorescence detection.
  
  
  RESULTS
  The H2O2 and SP mixture resulted in the greatest hydroxyl radical diffusion and was significantly greater than SP and water (P < .05) and H2O2 (P < .05). The addition of acidified thiourea resulted in higher radical diffusion, whereas the addition of neutral thiourea resulted in lower diffusion than H2O2 alone.
  
  
  CONCLUSIONS
  The SP and water mixture resulted in the lowest hydroxyl radical diffusion, and the H2O2 and SP mixture resulted in the greatest. Although the addition of acidified thiourea to H2O2 did not reduce radicals detected, the addition of neutral thiourea had a positive effect.
authors.affiliation: School of Dentistry, The University of Adelaide, Adelaide, South Australia, Australia. Electronic address: elizabeth.lou@gmail.com.
authors.forename: Elizabeth K
authors.initials: EK
authors.lastname: Lou
authors.affiliation: School of Dentistry, The University of Adelaide, Adelaide, South Australia, Australia.
authors.forename: Peter
authors.initials: P
authors.lastname: Cathro
authors.affiliation: School of Dentistry, The University of Adelaide, Adelaide, South Australia, Australia.
authors.forename: Victor
authors.initials: V
authors.lastname: Marino
authors.affiliation: School of Dentistry, The University of Adelaide, Adelaide, South Australia, Australia.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Damiani
authors.affiliation: School of Dentistry, The University of Adelaide, Adelaide, South Australia, Australia.
authors.forename: Geoffrey S
authors.initials: GS
authors.lastname: Heithersay
mesh_terms: D001641:Bicuspid; D001881:Borates / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D004058:Diffusion; D016166:Free Radical Scavengers / Q000737:chemistry*; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry*; D017665:Hydroxyl Radical / Q000737:chemistry*; D066298:In Vitro Techniques; D013499:Surface Properties; D013890:Thiourea / Q000737:chemistry*; D014073:Tooth Bleaching / Q000379:methods*
chemical_list: D001881:Borates; D016166:Free Radical Scavengers; D017665:Hydroxyl Radical; D006861:Hydrogen Peroxide; D013890:Thiourea; C027707:sodium perborate
keywords: Hydrogen peroxide; hydroxyl radical; intracoronal bleaching; thiourea