title: SEM-EDX study of prepared human dentine surfaces exposed to gingival retraction fluids.
abstract: OBJECTIVE
  To evaluate the effects of gingival retraction fluids (GRF) on prepared dentine surfaces, and to test the null-hypothesis that prior exposure of dentine surfaces for prolonged period to any of the fluids evaluated does not influence acid-etching of the exposed surfaces.
  
  
  METHODS
  The investigation was carried out using SEM and energy-dispersive X-ray analysis (EDX). The GRF studied were Hemodent (HMDT), Astringedent (AST) and Ultradent buffered 25% Aluminium Chloride (ULTB). Longitudinal sections of 220-grit ground dentine surfaces were exposed to GRF for 0.5-, 1-, 2- and 5-min (n=4 each). Another group of samples was produced by 20s application of 35% phosphoric acid (PA) on GRF-pretreated dentine. Control samples were not exposed to GRF. Differences in etching effect-a function of the Ca-contents detected by EDX, were analysed using Friedman's and Wilcoxon's rank test (P<0.05).
  
  
  RESULTS
  The SEM demonstrated the presence of a relatively non-porous amorphous dentine matrix, but many of the dentine tubule orifices remained occluded. Granular precipitates, which remained even after acid-etching, were noted on surfaces exposed to Hemodent for 5 min. Characteristic crystal growth was observed on surfaces exposed to Astringedent for 1- or 2-min prior to acid-etching. The EDX data demonstrated that there were differences in resulting Ca-content; ULTB >AST>HMDT>ULTB+PA>HMDT+PA>AST+PA>PA, but AST and HMDT were not significantly different.
  
  
  CONCLUSIONS
  The exposure of dentine prepared surfaces to these three GRF altered its morphology and reduced the dentine's susceptibility to acid-etching, thus the null-hypothesis is rejected.
authors.affiliation: Department of Community Dentistry, School of Dentistry, Room 6.43-2, Oral and Dental Hospital, University of Pretoria, P.O. box 1266, Pretoria 0001, South Africa. lekan.ayoyusuf@up.ac.za
authors.forename: Olalekan A
authors.initials: OA
authors.lastname: Ayo-Yusuf
authors.forename: Cornel H
authors.initials: CH
authors.lastname: Driessen
authors.forename: Andre J
authors.initials: AJ
authors.lastname: Botha
mesh_terms: D000134:Acid Etching, Dental; D003764:Dental Materials / Q000494:pharmacology*; D003804:Dentin / Q000187:drug effects* / Q000648:ultrastructure; D004577:Electron Probe Microanalysis / Q000379:methods; D006801:Humans; D008855:Microscopy, Electron, Scanning; D009930:Organic Chemicals / Q000494:pharmacology; D018709:Statistics, Nonparametric
chemical_list: D003764:Dental Materials; D009930:Organic Chemicals; C073695:Ultradent drying agent