title: Assessment of the role of cross section on fatigue resistance of rotary files when used in reciprocation.
abstract: OBJECTIVE
  The purpose of this study was to assess the role of cross section on cyclic fatigue resistance of One Shape, Revo-S SU, and Mtwo rotary files in continuous rotation and reciprocating motion in dynamic testing model.
  
  
  METHODS
  A total of 90 new rotary One Shape, Revo-S SU, and Mtwo files (ISO size 25, taper 0.06, length 25 mm) were subjected to continuous rotation or reciprocating motion. A cyclic fatigue testing device was fabricated with 60° angle of curvature and 5 mm radius. The dynamic testing of these files was performed using an electric motor which permitted the reproduction of pecking motion. All instruments were rotated or reciprocated until fracture occurred. The time taken for each instrument to fracture was recorded. All the fractured files were analyzed under a scanning electron microscope (SEM) to detect the mode of fracture. Statistical analysis was performed using one-way ANOVA, followed by Tukey's honestly significant differencepost hoctest.
  
  
  RESULTS
  The time taken for instruments in reciprocating motion to fail under cyclic loading was significantly longer when compared with groups in continuous rotary motion. There was a statistically significant difference between Mtwo rotary and the other two groups in both continuous and reciprocating motion. One Shape rotary files recorded significantly longer duration to fracture resistance when compared with Revo-S SU files in both continuous and reciprocating motion. SEM observations showed that the instruments of all groups had undergone a ductile mode of fracture.
  
  
  CONCLUSIONS
  Reciprocating motion improved the cyclic fatigue resistance of all tested groups.
authors.affiliation: Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Meenakshi Academy of Higher Education and Research, Chennai, Tamil Nadu, India.
authors.forename: Vadhana
authors.initials: V
authors.lastname: Sekar
authors.affiliation: Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Meenakshi Academy of Higher Education and Research, Chennai, Tamil Nadu, India.
authors.forename: Ranjith
authors.initials: R
authors.lastname: Kumar
authors.affiliation: Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Meenakshi Academy of Higher Education and Research, Chennai, Tamil Nadu, India.
authors.forename: Suresh
authors.initials: S
authors.lastname: Nandini
authors.affiliation: Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Meenakshi Academy of Higher Education and Research, Chennai, Tamil Nadu, India.
authors.forename: Suma
authors.initials: S
authors.lastname: Ballal
authors.affiliation: Department of Conservative Dentistry and Endodontics, Meenakshi Ammal Dental College and Hospital, Meenakshi Academy of Higher Education and Research, Chennai, Tamil Nadu, India.
authors.forename: Natanasabapathy
authors.initials: N
authors.lastname: Velmurugan
keywords: Cyclic fatigue; Mtwo system; One Shape rotary file; nickel–titanium; reciprocating files