title: Danger zone analysis using cone beam computed tomography after apical enlargement with K3 and K3XF in a manikin model.
abstract: BACKGROUND
  The objective of the study was to evaluate and compare how apical enlargement with K3 and K3XF nickel-titanium (NiTi) rotary instruments reduces the root thickness in the danger zone and affects canal transportation and centering ability in mandibular molar mesial canals in a manikin extracted tooth model.
  
  
  METHODS
  Seventy-two mesial root canals of first mandibular molars were instrumented. Initial and post-instrumentation Cone Beam Computed Tomography scans were performed after root canal preparation up to size 25, 30, 35 and 40 files. Canal transportation, canal centering and remaining root dentin thickness toward the danger zone were calculated in sections 1, 2 and 3 mm under the furcation level. Data were analyzed using non-parametric Kruskal-Wallis analysis of variance at a significance level ofP< 0.05.
  
  
  RESULTS
  K3 instruments removed more dentin toward the danger zone compared with K3XF instruments (P< .05) and significant differences in dentin thickness were found when canal enlargement was performed to a #35-40 with both systems (P< 0.05). No significant differences in canal transportation and centering ability were found between systems, except when canal enlargement was performed to a #40 (P= 0,0136). No differences were observed when comparing the number of uses in both systems (P> 0.05).
  
  
  CONCLUSIONS
  Under the conditions of this study K3 removed a significant amount of dentin at the furcation level compared with the R-Phase K3XF rotary system in curved root canals. Enlargement to a 35-40/04 file removed significantly more dentin with both systems.Key words:K3, K3XF, R-phase, center ability, canal transportation, dentin thickness, increased apical enlargement, danger zone, dentin thickness.
authors.affiliation: DDS, PhD. Department of Restorative Dentistry and Endodontics, Universitat Internacional de Catalunya.
authors.forename: Juan-Gonzalo
authors.initials: JG
authors.lastname: Olivier
authors.affiliation: DDS, PhD. Department of Restorative Dentistry and Endodontics, Universitat Internacional de Catalunya.
authors.forename: Marc
authors.initials: M
authors.lastname: García-Font
authors.affiliation: DDS, PhD. Department of Restorative Dentistry and Endodontics, Universitat Internacional de Catalunya.
authors.forename: Jose-Antonio
authors.initials: JA
authors.lastname: Gonzalez-Sanchez
authors.affiliation: MD, PhD. Department of Restorative Dentistry and Endodontics, Universitat Internacional de Catalunya.
authors.forename: Miguel
authors.initials: M
authors.lastname: Roig-Cayon
authors.affiliation: DDS, PhD. Department of Restorative Dentistry and Endodontics, Universitat Internacional de Catalunya.
authors.forename: Fernando
authors.initials: F
authors.lastname: Durán-Sindreu