title: Effects of ProTaper Universal, ProTaper Next, and HyFlex instruments on crack formation in dentin.
abstract: BACKGROUND
  The aim of the present study was to investigate the incidence of cracks in root dentin after root canal preparation with ProTaper Next (Dentsply Maillefer, Ballaigues, Switzerland), HyFlex (Coltene-Whaledent, Allstetten, Switzerland), and ProTaper Universal (Dentsply Maillefer) rotary instruments.
  
  
  METHODS
  One-hundred mandibular premolars were selected. Twenty-five teeth were left unprepared and served as a negative control; another 25 teeth were instrumented with the ProTaper Universal system up to size F4 as a positive control, and the remaining 50 teeth were shaped with the following experimental groups with an apical size 40 file: ProTaper Next X4 and HyFlex 40/0.4. After root canal preparation, all of the roots were sectioned perpendicular to the long axis at 2, 4, 6, and 8 mm from the apex, and the sections were then observed under a stereomicroscope. The absence/presence of cracks was recorded, and the data were analyzed with a chi-square test. The significance level was set at P = .05.
  
  
  RESULTS
  No cracks were observed in the negative control group. Vertical root fractures were not observed in any of the groups. The ProTaper Next and HyFlex instruments caused fewer cracks (28%) than the ProTaper Universal instrument (56%) (P < .05). However, there were no significant differences in crack formation between the ProTaper Next and HyFlex groups (P > .05).
  
  
  CONCLUSIONS
  Within the limitations of this in vitro study, all of the instrumentation systems used in this study created cracks in the root dentin. The ProTaper Next and HyFlex instruments tended to cause fewer dentinal cracks compared with the ProTaper Universal instrument.
authors.affiliation: Department of Endodontics, Faculty of Dentistry, İzmir Katip Çelebi University, İzmir, Turkey. Electronic address: capardt@hotmail.com.
authors.forename: Ismail Davut
authors.initials: ID
authors.lastname: Capar
authors.affiliation: Department of Endodontics, Faculty of Dentistry, Atatürk University, Erzurum, Turkey.
authors.forename: Hakan
authors.initials: H
authors.lastname: Arslan
authors.affiliation: Department of Pedodontics, Faculty of Dentistry, İzmir Katip Çelebi University, İzmir, Turkey.
authors.forename: Merve
authors.initials: M
authors.lastname: Akcay
authors.affiliation: Department of Endodontics, Faculty of Dentistry, İzmir Katip Çelebi University, İzmir, Turkey.
authors.forename: Banu
authors.initials: B
authors.lastname: Uysal
mesh_terms: D003722:Dental Alloys / Q000737:chemistry*; D003786:Dental Pulp Cavity / Q000293:injuries*; D003804:Dentin / Q000293:injuries*; D006801:Humans; D008422:Materials Testing; D009532:Nickel / Q000737:chemistry*; D010781:Photography / Q000379:methods; D018915:Root Canal Preparation / Q000295:instrumentation* / Q000379:methods; D012399:Rotation; D014025:Titanium / Q000737:chemistry*; D019415:Torque
chemical_list: D003722:Dental Alloys; C040654:titanium nickelide; D009532:Nickel; D014025:Titanium
keywords: Cracks; ProTaper Next; ProTaper Universal; controlled memory; dentinal damage; root canal instrumentation; root fracture; rotary nickel-titanium instruments