title: Effect of calcium hydroxide as a supplementary barrier in the radicular penetration of hydrogen peroxide during intracoronal bleaching in vitro.
abstract: OBJECTIVE
  To examine pH changes in the cervical external root surface, when calcium hydroxide was used as a supplementary barrier to the protective base material during intracoronal bleaching.
  
  
  METHODS
  Twenty-eight single-rooted human premolars extracted for orthodontic reasons were instrumented with K-Flex files, obturated with gutta-percha and subjected to thermocatalytic bleaching. The teeth were divided into four groups. In group A, a glass-ionomer cement barrier was placed at the cemento-enamel junction (CEJ) level and in group C, the barrier was placed 1 mm apical to the CEJ. In groups B and D, Ca(OH)2 was placed in contact and apical to the glass-ionomer cement at the CEJ and 1 mm apical to the CEJ, respectively. The teeth were placed in vials containing distilled water and the pH values of the medium surrounding the teeth were recorded after 1, 2, 4, 10 and 15 days, following renewal of the medium.
  
  
  RESULTS
  The pH in the medium became acidic in all groups. No statistically significant differences existed between groups for all the experimental days (P = 0.790).
  
  
  CONCLUSIONS
  The placement of Ca(OH)2 as a supplementary barrier during intracoronal bleaching did not have a significant effect in reversing the acidic pH created at the external root surface in vitro. Its potential effect during these procedures in vivo needs to be further investigated.
authors.affiliation: Department of Endodontology, School of Dentistry, Aristotle University of Thessaloniki, Thessaloniki, Greece.
authors.forename: T
authors.initials: T
authors.lastname: Lambrianidis
authors.forename: A
authors.initials: A
authors.lastname: Kapalas
authors.forename: M
authors.initials: M
authors.lastname: Mazinis
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001641:Bicuspid; D002126:Calcium Hydroxide / Q000737:chemistry*; D003736:Dental Cavity Lining / Q000379:methods*; D003786:Dental Pulp Cavity / Q000737:chemistry; D005899:Glass Ionomer Cements / Q000737:chemistry; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry* / Q000493:pharmacokinetics; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D014073:Tooth Bleaching / Q000379:methods*; D019237:Tooth Cervix / Q000737:chemistry; D014088:Tooth Permeability
chemical_list: D005899:Glass Ionomer Cements; D006861:Hydrogen Peroxide; D002126:Calcium Hydroxide