title: Effects of rotary instrumentation and different etchants on removal of smear layer on human dentin.
abstract: BACKGROUND
  Various methods of rotary preparation and conditioning of teeth affect surface topography and may affect the retention of dental restorations.
  
  
  OBJECTIVE
  This study microscopically evaluated dentin surfaces prepared by different rotary instruments and etched using several types of acid etchants that have been deemed suitable dentin conditioners.
  
  
  METHODS
  Occlusal surfaces of 35 extracted human molars were ground wet with 320-grit silicon carbide paper to the depth of the central groove and then prepared with diamond (n = 5) and finishing burs (n = 30). Five specimens from each group were used for SEM evaluation of mechanical preparation effects. Dentin specimens (n = 5) prepared with finishing burs were then etched with 1 of 5 etchants (25% polyacrylic acid, 10% phosphoric acid, 10% citric acid, 20% lactic acid, or 32% phosphoric acid) for 10 seconds. Specimens were critical-point dried and freeze fractured for SEM analysis.
  
  
  RESULTS
  Diamond rotary instruments created more undulating surfaces than finishing burs. Fine grooves were observed running perpendicular to undulations and parallel to the direction of instrument rotation. Specimens prepared with finishing burs exhibited a smooth surface interrupted by only a slight granularity. The amorphous smear layer was partially removed after the application of 25% polyacrylic acid (pH 1.53), but all dentinal tubules contained plugs. The number of dentin tubules containing plug material and the amount of material in the tubules decreased noticeably with 10% phosphoric acid (pH 0.86), and the dentin surface had an appearance similar to the specimen etched with 10% citric acid (pH 1.70). The surfaces treated with 20% lactic acid (pH 1.40) produced a clearly etched surface with minimal demineralization. Etching of dentin with 32% phosphoric acid (pH 0.16) revealed significant changes in dentin with the evidence of increased tubule diameter.
  
  
  CONCLUSIONS
  Differences related to the method of instrumentation were found in the surface characteristics of dentin. The degree of smear layer removal was related to the pH of the acid etchant.
authors.affiliation: College of Dentistry, University of Tanta, Tanta, Egypt. ayadmf@hotmail.com
authors.forename: M F
authors.initials: MF
authors.lastname: Ayad
mesh_terms: D000134:Acid Etching, Dental; D000180:Acrylic Resins / Q000494:pharmacology; D019343:Citric Acid / Q000494:pharmacology; D003754:Dental High-Speed Equipment; D003755:Dental High-Speed Technique; D003804:Dentin / Q000187:drug effects / Q000648:ultrastructure; D003806:Dentin Permeability; D018130:Diamond; D006801:Humans; D019344:Lactic Acid / Q000494:pharmacology; D008963:Molar; D010756:Phosphoric Acids / Q000494:pharmacology; D012399:Rotation; D016369:Smear Layer
chemical_list: D000180:Acrylic Resins; D010756:Phosphoric Acids; D019343:Citric Acid; D019344:Lactic Acid; C006903:carbopol 940; D018130:Diamond; C030242:phosphoric acid