title: Fracture strength of incisor crowns after intracoronal bleaching with sodium percarbonate.
abstract: OBJECTIVE
  To compare the fracture resistance of bovine teeth after intracoronal bleaching with sodium percarbonate (SPC) or sodium perborate (SP) mixed with water or 20% hydrogen peroxide (HP).
  
  
  METHODS
  Fifty extracted bovine teeth were divided into four experimental groups (G1-G4) and one control (n = 10) after endodontic treatment. Following root canal obturation, a glass ionomer barrier was placed at the cemento-enamel junction. After that, the pulp chambers were filled with: G1 - SP with water; G2 - SP with 20% HP; G3 - SPC with water; and G4 - SPC with 20% HP. No bleaching agent was used in the control group. Coronal access cavities were sealed with glass ionomer and specimens were immersed in artificial saliva. The bleaching agents were replaced after 7 days, and teeth were kept in artificial saliva for an additional 7 days, after which the pastes were removed and the coronal access cavities were restored with glass ionomer. Crowns were subjected to compressive load at a cross head speed of 0.5 mm min(-1) applied at 135° to the long axis of the root by an EMIC DL2000 testing machine, until coronal fracture. Data were statistically analysed by anova and Tukey test.
  
  
  RESULTS
  No differences in fracture resistance were observed between the experimental groups (P > 0.05). However, all experimental groups presented lower fracture resistance than the control group (P < 0.05).
  
  
  CONCLUSIONS
  SPC and SP led to equal reduction on fracture resistance of dental crowns, regardless of being mixed with water or 20% HP.
authors.affiliation: Departments of Restorative Dentistry Dental Materials and Prosthodontics, Araraquara Dental School, University Estadual Paulista, Araraquara, São Paulo, Brazil. kuga@foar.unesp.br
authors.forename: Milton Carlos
authors.initials: MC
authors.lastname: Kuga
authors.forename: José Mauricio
authors.initials: JM
authors.lastname: dos Santos Nunes Reis
authors.forename: Semíramis
authors.initials: S
authors.lastname: Fabrício
authors.forename: Idomeo
authors.initials: I
authors.lastname: Bonetti-Filho
authors.forename: Edson Alves
authors.initials: EA
authors.lastname: de Campos
authors.forename: Gisele
authors.initials: G
authors.lastname: Faria
mesh_terms: D000818:Animals; D057886:Bleaching Agents / Q000009:adverse effects*; D001881:Borates / Q000009:adverse effects*; D002254:Carbonates / Q000009:adverse effects*; D002417:Cattle; D003442:Crowns; D006861:Hydrogen Peroxide / Q000009:adverse effects*; D014073:Tooth Bleaching / Q000009:adverse effects* / Q000379:methods; D014082:Tooth Fractures / Q000209:etiology
chemical_list: D057886:Bleaching Agents; D001881:Borates; D002254:Carbonates; D006861:Hydrogen Peroxide; C027707:sodium perborate; C034738:sodium percarbonate