title: Comparison of first accessory cone penetration after using stainless-steel and ni-ti spreaders in curved resin blocks.
abstract: BACKGROUND
  The purpose of this study was to compare first accessory gutta-percha penetration after the use of nickel-titanium (Ni-Ti) or stainless-steel spreaders in curved resin blocks.
  
  
  METHODS
  Forty resin blocks with 30º and 45º curvatures (20 blocks for each) were prepared and #30 master cones were placed in canals. In part one, under 20 Newton pressure, Ni-Ti or stainless-steel spreaders were placed alongside the master cone and their penetration was measured with a millimeter ruler. In part two, after removing the spreader, one of the accessory cones (#15, #20 or MF) was substituted in the canal and its penetration was measured. The Mann-U Whitney test was used for the final evaluation.
  
  
  RESULTS
  In both curvatures, the penetration of Ni-Ti spreaders were significantly more than stainless-steel spreaders (p<0.005). Penetration of the first accessory cones (#15 and MF) in Ni- Ti spreader group were also significantly more than stainless-steel group (p<0.05) (in both curvature groups).
  
  
  CONCLUSIONS
  This study showed that Ni-Ti spreaders and #15 accessory cones penetrated deeper in curved canals than stainless spreaders and #15 accessory cones. Therefore, the use of NiTi spreader in lateral condensation technique is suggested for better results.
authors.affiliation: Department of Endodontic, Dental School of Islamic Azad University and Iranian Center for Endodontic Research, Tehran, Iran.
authors.forename: Nahid
authors.initials: N
authors.lastname: Mohammadzade Akhlaghi
authors.forename: Nasrin
authors.initials: N
authors.lastname: Roghanizad
authors.forename: Zohreh
authors.initials: Z
authors.lastname: Khalilak
authors.forename: Neda
authors.initials: N
authors.lastname: Rezaie
keywords: Gutta-Percha; Nickel-Titanium; Root Canal Obturation; Stainless-Steel