title: Preparation of curved root canals with rotary FlexMaster instruments compared to Lightspeed instruments and NiTi hand files.
abstract: OBJECTIVE
  To compare the recently introduced rotary FlexMaster instruments with Lightspeed instruments and NiTi hand files in preparing curved root canals.
  
  
  METHODS
  Root canals of extracted molars were shaped with rotary FlexMaster instruments ('FM': n = 45), Lightspeed instruments ('LS': n = 46), and NiTi hand files (n = 45) using the balanced-force technique. The apical preparation size was 40. Root canal instrumentation was carried out in a phantom head under clinical conditions. A re-assembly technique allowed a comparison of the canal outline before and after preparation. Root sections 2.5 mm short of working length were used to calculate the percentage of prepared canal outline (= PPO) and the amount of root canal transportation. Loss of working length, fracture rate and time spent on complete preparation were also recorded.
  
  
  RESULTS
  The highest PPO values were found in the LS group (mean = 63% [95% CI: 55%; 70%]). Although not statistically significant, lower PPO values were detected for FM instruments (mean = 55% [95% CI: 49%; 62%]) and for hand files (mean = 53% [95% CI: 47%; 59%]). The incidence of root canal transportation exceeding 0.1 mm was significantly lower in the LS group than in the FM group. Loss of working length of 0.5 mm occurred in five cases (LS group: 4x; FM group: 1x). Two LS instruments fractured. Half the time was needed for root canal preparation with FM instruments than with hand files.
  
  
  CONCLUSIONS
  Rotary FM instruments are suitable for preparing curved root canals. They provided results similar to LS instruments with minimal risk of instrument fracture but increased risk of root canal transportation.
authors.affiliation: Department of Conservative Dentistry, School of Dental Medicine, University of Tübingen, Tübingen, Germany. roland.weiger@unibas.ch
authors.forename: R
authors.initials: R
authors.lastname: Weiger
authors.forename: M
authors.initials: M
authors.lastname: Brückner
authors.forename: A
authors.initials: A
authors.lastname: ElAyouti
authors.forename: C
authors.initials: C
authors.lastname: Löst
mesh_terms: D003722:Dental Alloys; D003786:Dental Pulp Cavity / Q000033:anatomy & histology*; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D008348:Manikins; D008422:Materials Testing; D009532:Nickel; D018915:Root Canal Preparation / Q000295:instrumentation* / Q000379:methods; D012399:Rotation; D013997:Time Factors; D014025:Titanium
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium