title: Ultrastructural morphologic evaluation of root canal walls prepared by two rotary nickel-titanium systems: a comparative study.
abstract: OBJECTIVE
  To evaluate and compare the ultrastructural morphology, surface cleanliness, and roughness of root canal walls of extracted teeth after instrumentation with 2 different rotary nickel-titanium systems (ProTaper and NRT) when associated with the use of sodium hypochlorite and ethylenediaminetetraacetic acid combination as an irrigating regimen.
  
  
  METHODS
  A total of 40 freshly extracted single-rooted human mandibular premolars with fully developed apices and straight roots were selected. The roots were randomly divided into 2 experimental groups of 20 samples each according to the rotary system used in the preparation of the canals. In group I, canals were instrumented using the ProTaper file system; in group II, canals were prepared by the NRT file system. For each sample, an overall evaluation of the dentin surface along the whole length of the canal and a specific evaluation of the root dentin at the apical third was carried out regarding presence of debris, quality and amount of smear layer, and roughness using stereomicroscope and scanning electron microscope. Energy-dispersive spectroscopy was further used to detect nickel-titanium alloy remnants on the root dentinal surface of 2 randomly selected samples within each group.
  
  
  RESULTS
  Statistical analysis showed no significant difference between the tested systems regarding debris and smear layer. The ProTaper system presented significantly smoother dentinal walls at the apical level than the NRT system. Alloy remnants were detected within the dentinal walls instrumented by both systems.
  
  
  CONCLUSIONS
  Both systems produced relatively clean and debris-free dentin surfaces in the coronal thirds and to a lesser extent in the middle thirds. In contrast, these instruments were unable to produce a dentin surface free from smear layer and debris in the apical thirds. Smoother prepared walls could be achieved using ProTaper files. Remnants of nickel-titanium alloy were detected on the root dentin surface instrumented by both systems.
authors.affiliation: Department of Endodontics, Dental School, Cairo University, Cairo, Egypt. nihalsabet@yahoo.com
authors.forename: Nihal Ezzat
authors.initials: NE
authors.lastname: Sabet
authors.forename: Reem A
authors.initials: RA
authors.lastname: Lutfy
mesh_terms: D001641:Bicuspid; D003722:Dental Alloys / Q000032:analysis; D003762:Dental Instruments; D003786:Dental Pulp Cavity / Q000648:ultrastructure*; D003804:Dentin / Q000648:ultrastructure; D004577:Electron Probe Microanalysis; D006801:Humans; D008855:Microscopy, Electron, Scanning; D009532:Nickel / Q000032:analysis; D012388:Root Canal Irrigants; D018915:Root Canal Preparation / Q000295:instrumentation*; D016369:Smear Layer; D014025:Titanium / Q000032:analysis
chemical_list: D003722:Dental Alloys; D012388:Root Canal Irrigants; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium