title: Demineralization effects of hydrogen peroxide on bovine enamel and relation to shear bond strength of brackets.
abstract: OBJECTIVE
  To measure the demineralization capacity of 37% phosphoric acid and shear bond strength (SBS) of brackets attached on bovine enamel at different times after bleaching with 30% hydrogen peroxide.
  
  
  METHODS
  Four equally-sized pieces of each crown from 18 bovine incisors were randomly distributed among 7 groups (n = 10). After bleaching with 30% hydrogen peroxide for 1 h, specimens were stored in artificial saliva for 0 h, 24 h, or 1, 2, 3, or 4 weeks before bonding specimens to brackets. An unbleached group of specimens served as controls. Shear bond strength (SBS in MPa) was measured with a universal testing machine. Adhesive Remnant Index (ARI) scores were determined after failure of bracket bonds. To measure demineralized Ca2+, four 4 x 4 mm sections from each of 15 bovine incisors were randomly distributed among 4 groups (n = 15). Specimens were stored in artificial saliva for 0 h, 24 h or 7 days after bleaching and then immersed in 37% phosphoric acid solution. After 15 s, 30 s, and 60 s, 5-ml aliquots of solution were removed for spectrophotometry. Unbleached specimens served as controls.
  
  
  RESULTS
  Larger amounts of Ca2+ were extracted from the enamel by phosphoric acid up to 24 h after application of hydrogen peroxide, when there was also a significant decrease in bracket-enamel SBS. After 1 week, there were no changes in amounts of Ca2+ extracted, and SBS values returned towards unbleached values.
  
  
  CONCLUSIONS
  Lower bracket-enamel SBS values at 24 h after bleaching are closely correlated with the larger amounts of Ca2+ extracted from the enamel.
authors.affiliation: Department of Pathology and Dental Therapeutics, Faculty of Dentistry, University of Granada, Granada, Spain. sglopez@ugr.es
authors.forename: Santiago
authors.initials: S
authors.lastname: González-López
authors.forename: Carmen Lucia Soares G
authors.initials: CL
authors.lastname: de Medeiros
authors.forename: Camejo-Aguilar
authors.initials: CA
authors.lastname: Defren
authors.forename: Maria Victoria
authors.initials: MV
authors.lastname: Bolaños-Carmona
authors.forename: Purificación
authors.initials: P
authors.lastname: Sanchez-Sanchez
authors.forename: Mario
authors.initials: M
authors.lastname: Menendez-Nuñez
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods; D000818:Animals; D002118:Calcium / Q000032:analysis; D002417:Cattle; D001840:Dental Bonding; D017005:Dental Debonding; D003743:Dental Enamel / Q000187:drug effects*; D003799:Dental Stress Analysis; D006861:Hydrogen Peroxide / Q000008:administration & dosage / Q000009:adverse effects*; D016910:Orthodontic Brackets; D016877:Oxidants / Q000008:administration & dosage / Q000009:adverse effects*; D010756:Phosphoric Acids; D011897:Random Allocation; D033081:Shear Strength; D013054:Spectrophotometry, Atomic; D014073:Tooth Bleaching / Q000009:adverse effects*; D017001:Tooth Demineralization / Q000139:chemically induced*
chemical_list: D016877:Oxidants; D010756:Phosphoric Acids; D006861:Hydrogen Peroxide; C030242:phosphoric acid; D002118:Calcium