title: Morphological field emission-SEM study of the effect of six phosphoric acid etching agents on human dentin.
abstract: OBJECTIVE
  This study evaluated the effects of six phosphoric acid-etching agents on dentin, the independent variables being two acid concentrations (10% and 32%-37%) and three thickener conditions (no thickener, silica, and polymer). The tested hypothesis was that the use of different etchants with similar concentrations of phosphoric acid would result in similar depths of dentin demineralization.
  
  
  METHODS
  Thirty dentin disks were obtained from extracted human teeth by microtome sectioning. The dentin surfaces were etched with one of the etching agents, fixed, dehydrated and dried. The specimens were observed using a FE-SEM. The mean deepest demineralization of intertubular dentin was measured from fracture surfaces of the disks. These values were analyzed by ANOVA and Duncan's Test. The morphological appearance of the dentin surfaces was compared using the following observation criteria: 1) Presence of a cuff of peritubular dentin; 2) Relative thickness of the layer containing residual collagen or smear layer particles; and 3) Formation of a submicron hiatus at the bottom of the exposed collagen network. The pH of each of the etching agents was measured. A correlation analysis was made of the pH vs. the depth of dentin demineralization.
  
  
  RESULTS
  Silica-thickened etchants did not demineralize dentin as deeply as did polymer-thickened etchants and unthickened etchants. High magnifications revealed three distinct zones within the demineralized dentin layer; an upper porous zone of residual smear layer or denatured collagen and residual silica particles (in groups etched with silica-thickened etchants), an intermediate area with randomly oriented collagen fibers, and a lower zone with submicron hiatus, few collagen fibers, and scattered hydroxyapatite inclusions. This hiatus was observable in all the specimens etched with the polymer-thickened etchants, in 90% of the specimens etched with the unthickened phosphoric acid liquids, and in 60% of the specimens etched with the silica-thickened gels.
  
  
  CONCLUSIONS
  The results obtained suggest that similar concentrations of phosphoric acid etchants containing distinct thickeners result in different demineralization depths as well as different morphology of etched dentin.
authors.affiliation: Instituto Superior de Ciências da Saude, School of Dentistry, Monte da Caparica, Portugal.
authors.forename: J
authors.initials: J
authors.lastname: Perdigão
authors.forename: P
authors.initials: P
authors.lastname: Lambrechts
authors.forename: B
authors.initials: B
authors.lastname: van Meerbeek
authors.forename: A R
authors.initials: AR
authors.lastname: Tomé
authors.forename: G
authors.initials: G
authors.lastname: Vanherle
authors.forename: A B
authors.initials: AB
authors.lastname: Lopes
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods*; D000704:Analysis of Variance; D003804:Dentin / Q000737:chemistry / Q000187:drug effects* / Q000648:ultrastructure; D004339:Drug Compounding; D005782:Gels; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008855:Microscopy, Electron, Scanning; D010756:Phosphoric Acids / Q000737:chemistry* / Q000494:pharmacology*; D011135:Polysaccharides, Bacterial; D012822:Silicon Dioxide; D016369:Smear Layer; D017001:Tooth Demineralization
chemical_list: D005782:Gels; D010756:Phosphoric Acids; D011135:Polysaccharides, Bacterial; D012822:Silicon Dioxide; C030242:phosphoric acid; C002563:xanthan gum