title: Less extrusion debris during the retreatment of curved canals using twisted files with higher rotational speeds: an ex vivo study.
abstract: BACKGROUND
  Debris extrusion from the apical foramen can be problematic in severely curved canals. This study aimed to assess the use of Twisted Files (TF) at different rotational speeds during retreatment, compared with manual technique using Triple-Flex Files (TFF).
  
  
  METHODS
  Forty-eight mesiobuccal root canals were randomized to four groups (n = 12 per group). In groups A, B, and C, gutta-percha was removed using TF at 500, 1000, and 1500 rpm, respectively, while it was removed using TFF in group D. Apical debris was collected in a pre-weighed centrifuge tube. The weight of dry debris was assessed by comparing the pre- and post-instrumentation weight for each group.
  
  
  RESULTS
  Instrumentation in group D (0.69 ± 0.04 mg) extruded significantly more debris than any of the TF groups (A: 0.54 ± 0.05 mg; B: 0.48 ± 0.04 mg; C: 0.42 ± 0.03 mg; all P < 0.001). In addition, increasing the rotational speed of TF decreased the amount of extruded debris (A vs. B: P = 0.006; B vs. C: P < 0.001; A vs. C: P < 0.001).
  
  
  CONCLUSIONS
  TF at 1500 rpm produced less apical extrusion debris than other TF operating speeds and TFF.
authors.affiliation: School of Dentistry, Shandong University, 44, Wenhua West Road, Jinan, 250012, Shandong Province, China.|School of Stomatology, Qingdao University, Qingdao, 266021, Shandong Province, China.
authors.forename: Mengdong
authors.initials: M
authors.lastname: Liu
authors.affiliation: School of Dentistry, Shandong University, 44, Wenhua West Road, Jinan, 250012, Shandong Province, China. xiongshijiangdr@sohu.com.
authors.forename: Shijiang
authors.initials: S
authors.lastname: Xiong
authors.affiliation: School of Stomatology, Qingdao University, Qingdao, 266021, Shandong Province, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Tan
authors.affiliation: School of Stomatology, Qingdao University, Qingdao, 266021, Shandong Province, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Liu
mesh_terms: D003762:Dental Instruments; D003786:Dental Pulp Cavity / Q000601:surgery*; D004867:Equipment Design; D006171:Gutta-Percha; D006801:Humans; D066298:In Vitro Techniques; D011897:Random Allocation; D019233:Retreatment; D012387:Root Canal Filling Materials; D012389:Root Canal Obturation / Q000295:instrumentation*; D012399:Rotation
chemical_list: D012387:Root Canal Filling Materials; D006171:Gutta-Percha
keywords: Apical debris; Root canal therapy; Rotational speed; Tooth apex; Triple-Flex Files; Twisted Files