title: Comparative Evaluation of Physical Surface Changes and Incidence of Separation in Rotary Nickel-Titanium Instruments: An in Vitro SEM Study.
abstract: BACKGROUND
  The aim of the present study was to comparatively evaluate the physical surface changes and incidence of separation in rotary nickel-titanium (NiTi) instruments using scanning electron microscope (SEM).
  
  
  METHODS
  A total number of 210 freshly extracted human maxillary and mandibular first molars were selected and distributed between three groups. Three different systems of rotary NiTi instruments, namely ProFile (PF), RaCe (RC) and Twisted File (TF), were used to prepare the canals using crown-down technique. All instruments were evaluated by means of SEM with 500× and 1500× magnifications, at four different stages; before use, after preparation of 7 and 14 canals and after instrument separation. Photomicrographs were also taken. The data was analyzed using the Kruskal-Wallis test and the level of significance was set at 0.001. It was found that H (HAT matrix) was 15.316 with 2 degrees of freedom. Moreover the various groups were compared using the Student-Newman-Keuls test with P<0.05 and it was found that all groups were significantly different.
  
  
  RESULTS
  RC showed the maximum wear of the surface followed by TF (P<0.05). PF showed the minimum wear except for its tip. There was no correlation between electropolishing and file fracture. Insignificant difference was observed in the mean number of canals shaped by PF and TF before their separation.
  
  
  CONCLUSIONS
  Clinically, TF performance was superior, followed by PF then RC. RC fracture rate was the greatest after preparing the least number of canals.
authors.affiliation: Department of Conservative Dentistry and Endodontics, Institute of Dental Sciences, Jammu, India.
authors.forename: Rudra
authors.initials: R
authors.lastname: Kaul
authors.affiliation: Department of Conservative Dentistry and Endodontics, Government Dental College and Hospital, Srinagar, India.
authors.forename: Riyaz
authors.initials: R
authors.lastname: Farooq
authors.affiliation: Department of Oral Medicine and Radiology, Government Dental College and Hospital, Srinagar, India.
authors.forename: Vibhuti
authors.initials: V
authors.lastname: Kaul
authors.affiliation: Department of Conservative Dentistry and Endodontics, Government Dental College and Hospital, Srinagar, India.
authors.forename: Shafayat Ullah
authors.initials: SU
authors.lastname: Khateeb
authors.affiliation: Department of Conservative Dentistry and Endodontics, Government Dental College and Hospital, Srinagar, India.
authors.forename: Aamir Rashid
authors.initials: AR
authors.lastname: Purra
authors.affiliation: Department of Oral Medicine and Radiology, Government Dental College and Hospital, Srinagar, India.
authors.forename: Roopali
authors.initials: R
authors.lastname: Mahajan
keywords: Fatigue; Nickel-Titanium Alloy; Physical Surface Change; Profile; RaCe; SEM; Scanning Electron Microscopy; Stainless Steel; Torsional Force; Twisted File