title: Lifespan of one nickel-titanium rotary file with reciprocating motion in curved root canals.
abstract: BACKGROUND
  The purpose of this study was to examine the lifespan of one nickel-titanium (NiTi) rotary file when used in reciprocating motion and to compare the time required for its preparation of a curved root canal using both reciprocating and continuous motion.
  
  
  METHODS
  One hundred twenty curved canals from 60 extracted maxillary and mandibular molars were selected for measuring the mean number of uses. Each canal was prepared with reciprocating motion until the ProTaper F2 single file (Dentsply Maillefer, Ballaigues, Switzerland) reached the working length. One file was used until it was fractured. Another 60 canals were divided into two groups. 30 canals in the continuous rotation motion (CM) group were prepared using continuous rotation following the sequence of ProTaper files, whereas the canals in the reciprocating motion (RM) group (n = 30) were prepared with reciprocating motion with the sole use of the ProTaper F2. The total root canal preparation time was measured until the F2 file finally reached the working length in both groups.
  
  
  RESULTS
  A total of 11 files were used in the preparation of 120 curved root canals. The average lifespan of one F2 file was 10.60 ± 4.35 canals with the longest lifespan of 21 canals. The total time for canal preparation was 46.42 ± 18.12 seconds and 21.15 ± 6.70 seconds in the CM and RM groups, respectively. There was a statistically significant difference between the groups (p < 0.01).
  
  
  CONCLUSIONS
  Within the limitation of this study, one F2 file can be safely used to the working length of curved canals at least six times under reciprocating motion. Reciprocating preparation with only one F2 file was much faster than root canal instrumentation with continuous rotation.
authors.affiliation: Department of Conservative Dentistry, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Korea.
authors.forename: Sung-Yeop
authors.initials: SY
authors.lastname: You
authors.forename: Kwang-Shik
authors.initials: KS
authors.lastname: Bae
authors.forename: Seung-Ho
authors.initials: SH
authors.lastname: Baek
authors.forename: Kee-Yeon
authors.initials: KY
authors.lastname: Kum
authors.forename: Won-Jun
authors.initials: WJ
authors.lastname: Shon
authors.forename: Woocheol
authors.initials: W
authors.lastname: Lee
mesh_terms: D003722:Dental Alloys; D003762:Dental Instruments; D003786:Dental Pulp Cavity / Q000033:anatomy & histology*; D004209:Disposable Equipment; D004868:Equipment Failure; D017743:Equipment Reuse; D006801:Humans; D008963:Molar; D009038:Motion; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation* / Q000379:methods; D013997:Time Factors; D014025:Titanium
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium