title: Pattern of Hydroxyapatite Crystal Growth on Bleached Enamel Following the Application of Two Antioxidants: An Atomic Force Microscope Study.
abstract: OBJECTIVE
  This study observed the topographical pattern of hydroxyapatite deposition and growth (D&G) on bleached enamel following application of two antioxidants (sodium ascorbate and catalase) using atomic force microscope.
  
  
  METHODS
  Twenty enamel specimens (4×3×2mm), prepared from extracted impacted third molars, were mounted in self-cure acrylic and randomly grouped as: Group I-untreated; Group II- 35%H2O2; Group III- 35%H2O2+ artificial saliva; Group IV- 35%H2O2+ catalase+ artificial saliva; Group V- 35%H2O2+ sodium ascorbate+ artificial saliva. Groups I and II were observed immediately after treatment. Groups III-V were observed after 72 hrs. Roughness average was also calculated and analyzed with non-parametric Kruskall-Wallis ANOVA and Mann-Whitney tests.
  
  
  RESULTS
  H2O2dissolved matrix, exposed hydroxyapatite crystals (HACs), causing dissolution on the sides of and within HACs and opening up of nano-spaces. Artificial saliva showed growth of dissoluted crystals. Antioxidants+saliva showed potentiated remineralization by D&G on dissoluted HACs of bleached enamel. Catalase potentiated blockshaped, while sodium ascorbate the needle-shaped crystals with stair-pattern of crystallization. Evidence of oxygen bubbles was a new finding with catalase. Maximum roughness average was in group V followed by group II > group IV > group III > group I.
  
  
  CONCLUSIONS
  Post-bleaching application of catalase and sodium ascorbate potentiated remineralization by saliva, but in different patterns. None of the tested antioxidant could return the original topography of enamel.
authors.forename: Chitra P
authors.initials: CP
authors.lastname: Bhusari
authors.forename: Divya S
authors.initials: DS
authors.lastname: Sharma
mesh_terms: D000975:Antioxidants / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000494:pharmacology; D002374:Catalase / Q000494:pharmacology; D003460:Crystallization; D003743:Dental Enamel / Q000187:drug effects / Q000648:ultrastructure*; D017886:Durapatite / Q000737:chemistry*; D006801:Humans; D018625:Microscopy, Atomic Force; D014073:Tooth Bleaching
chemical_list: D000975:Antioxidants; D017886:Durapatite; D002374:Catalase; D001205:Ascorbic Acid
keywords: antioxidants; atomic force microscope; catalase; dental bleaching; sodium ascorbate