title: In vitroevaluation of efficacy of different rotary instrument systems for gutta percha removal during root canal retreatment.
abstract: BACKGROUND
  Complete removal of old filling material during root canal retreatment is fundamental for predictable cleaning and shaping of canal anatomy. Most of the retreatment methods tested in earlier studies have shown inability to achieve complete removal of root canal filling. Therefore the aim of this investigation was to assess the efficacy of three different rotary nickel titanium retreatment systems and Hedstrom files in removing filling material from root canals.
  
  
  METHODS
  Sixty extracted mandibular premolars were decoronated to leave 15 mm root. Specimen were hand instrumented and obturated using gutta percha and AH plus root canal sealer. After storage period of two weeks, roots were retreated with three (Protaper retreatment files, Mtwo retreatment files, NRT GPR) rotary retreatment instrument systems and Hedstroem files. Subsequently, samples were sectioned longitudinally and examined under stereomicroscope. Digital images were recorded and evaluated using Digital Image Analysing Software. The retreatment time was recorded for each tooth using a stopwatch. The area of canal and the residual filling material was recorded in mm2 and the percentage of remaining filling material on canal walls was calculated. Data was analysed using ANOVA test.
  
  
  RESULTS
  Significantly less amount of residual filling material was present in protaper and Mtwo instrumented teeth (p< 0.05) compared to NRT GPR and Hedstrom files group. Protaper instruments also required lesser time during removal of filling material followed by Mtwo instruments, NRT GPR files and Hedstrom files.
  
  
  CONCLUSIONS
  None of the instruments were able to remove the filling material completely from root canal. Protaper universal retreatment system and Mtwo retreatment files were more efficient and faster compared to NRT GPR fles and Hedstrom files.Key words:Gutta-percha removal, nickel titanium, root canal retreatment, rotary instruments.
authors.affiliation: MDS. Conservative Dentistry and Endodontics, D.A.P.M.R.V. Dental College, Bangalore, India.
authors.forename: Mercy
authors.initials: M
authors.lastname: Joseph
authors.affiliation: Senior Resident. Department of Conservative Dentistry and Endodontics, Maulana Azad Institute of Dental Sciences, New Delhi, India.
authors.forename: Jyoti
authors.initials: J
authors.lastname: Ahlawat
authors.affiliation: Senior Resident. Department of Conservative Dentistry and Endodontics, Maulana Azad Institute of Dental Sciences, New Delhi, India.
authors.forename: Amit
authors.initials: A
authors.lastname: Malhotra
authors.affiliation: Professor. Department of Conservative Dentistry and Endodontics, D.A.P.M.R.V. Dental College, Bangalore, India.
authors.forename: Murali
authors.initials: M
authors.lastname: Rao
authors.affiliation: MDS. Oral and Maxillofacial Surgery, ESIC Hospital, Rohini, New Delhi, India.
authors.forename: Abhimanyu
authors.initials: A
authors.lastname: Sharma
authors.affiliation: Professor. Department of Conservative Dentistry and Endodontics, Maulana Azad Institute of Dental Sciences New Delhi, India.
authors.forename: Sangeeta
authors.initials: S
authors.lastname: Talwar