title: A comparative evaluation of the canal centering ability of three rotary nickel-titanium retreatment systems in the mesio-buccal canals of mandibular first molars using computed tomography.
abstract: BACKGROUND
  During endodontic retreatment, relative difficulty exists in removing the filling material and maintaining the canal anatomy. Usage of nickel-titanium (NiTi) rotary retreatment instruments is widely accepted, but there is a lack of adequate literature evidence about their canal centering ability.
  
  
  OBJECTIVE
  To compare the canal centering ability of rotary NiTi retreatment systems.
  
  
  METHODS
  Mandibular first molars with mesiobuccal canals with canal access angle of 20-40° were used. Canals prepared until ISO 25, 0.06 taper. Obturated with three different techniques lateral compaction, Thermafil, and Resilon/Epiphany. Retreatment was carried using three different systems ProTaper retreatment, Mtwo R and REndo. Specimens were subjected to computed tomography analysis at coronal, middle, and apical third of the root canal preobturation and postretreatment procedure.
  
  
  METHODS
  One-way ANOVA and post-hoc Tukey test.
  
  
  RESULTS
  No statistically significant difference with three retreatment systems. Variation existed among all the subgroups at the coronal, middle, and apical third of the root canal.
  
  
  CONCLUSIONS
  All retreatment systems with three obturation techniques showed eccentricity within acceptable limits. REndo, MtwoR showed better canal centering and ProTaper retreatment system showed tendency for eccentric canal preparation, especially in apical third.
authors.affiliation: Department of Conservative Dentistry and Endodontics, Faculty of Dental Sciences, Sri Ramachandra University, Porur, Chennai, Tamil Nadu, India.
authors.forename: Deenadhayalan
authors.initials: D
authors.lastname: Gogulnath
authors.affiliation: Department of Conservative Dentistry and Endodontics, Faculty of Dental Sciences, Sri Ramachandra University, Porur, Chennai, Tamil Nadu, India.
authors.forename: Rajendran Mathan
authors.initials: RM
authors.lastname: Rajan
authors.affiliation: Department of Conservative Dentistry and Endodontics, Faculty of Dental Sciences, Sri Ramachandra University, Porur, Chennai, Tamil Nadu, India.
authors.forename: Ganesh
authors.initials: G
authors.lastname: Arathy
authors.affiliation: Department of Conservative Dentistry and Endodontics, Faculty of Dental Sciences, Sri Ramachandra University, Porur, Chennai, Tamil Nadu, India.
authors.forename: Deivanayagam
authors.initials: D
authors.lastname: Kandaswamy
keywords: Canal centering ability; canal access angle; computed tomography