title: Refinement influence in the cleaning efficacy of rotary nickel-titanium Mtwo instruments in oval-shaped canals by means of optical microscopy.
abstract: OBJECTIVE
  This study evaluated the cleaning efficacy of the rotary nickel-titanium Mtwo by means of optical microscopy in oval-shaped root canals and compared refinement influence using ultrasonic files or Hedströem files.
  
  
  METHODS
  Twenty mandibular incisors were accessed, included in epoxy resin blocks, and cut transversely at 3, 6, and 9 mm from the apex. Teeth were instrumented using rotary nickel-titanium Mtwo. Digital images of the root cross sections were obtained before and after instrumentation with a digital camera attached to an optical microscope. Subsequently, samples were randomly divided into two groups for refinement. Group I was refined using ultrasonic files #30 and group II with Hedströem files #30. Final digital images of cross sections after refinement were captured and analyzed. The boundaries for the uninstrumented perimeter were measured by the software ImageTool 3.0. The data obtained were statistically analyzed by analysis of variance (ANOVA) and t-test.
  
  
  RESULTS
  Mtwo instrumentation produced 41.48% of the uninstrumented perimeter. The final refinement using Hedströem and ultrasonic files decreased the uninstrumented perimeter. Significant differences (t-test, P = 0.00) were found at the three thirds after the final refinement, except for the apical third that was enhanced by Hedströem file. However, there was no statistical difference between the two refinement techniques used (P > 0.05). Mtwo instrumentation was not capable of cleaning and shaping the entire perimeter of the root canals walls.
  
  
  CONCLUSIONS
  The final refinement, either with ultrasonic files or with Hedströem files, resulted in significantly less uninstrumented perimeter.
authors.forename: Cibella Maymone
authors.initials: CM
authors.lastname: Pontes
authors.affiliation: Department of Proclin, School of Dentistry, Rio de Janeiro State University, Rio de Janeiro, RJ, Brazil.
authors.forename: Luciana Moura
authors.initials: LM
authors.lastname: Sassone
authors.forename: Cristiana Francescutti
authors.initials: CF
authors.lastname: Murad
authors.forename: Rivail Antônio Sérgio
authors.initials: RA
authors.lastname: Fidel
authors.forename: Fernando Sili
authors.initials: FS
authors.lastname: Vilhena
mesh_terms: D003762:Dental Instruments / Q000592:standards*; D008853:Microscopy / Q000379:methods*; D013242:Sterilization / Q000379:methods*; D014025:Titanium
chemical_list: D014025:Titanium