title: Influence of the diameter and taper of root canals on the removal efficiency of Thermafil Plus plastic carriers using ProTaper Retreatment Files.
abstract: BACKGROUND
  This study aimed to investigate the influence of canal shape on the time required for the removal of Thermafil Plus plastic carriers (Dentsply Tulsa Dental, Tulsa, OK) using ProTaper Retreatment Files (Dentsply Maillefer, Ballaigues, Switzerland).
  
  
  METHODS
  Sixty simulated J-shaped canals in resin blocks were divided into six groups prepared differently in terms of apical size (25/04 or 35/06) and coronal enlargement (no coronal enlargement, using a K3 orifice opener [SybronEndo, Orange, CA] 25/08, or using Gates-Glidden drills [Mani, Tochigi, Japan] #1-4) and were filled with a Thermafil Plus of the same carrier size (size 25 or 35). The carriers were removed using ProTaper D1, D2, and D3 in a crown-down sequence, and removal time was measured. A similar experiment was performed using extracted mandibular incisors prepared to 25/04 with or without coronal enlargement using Gates-Glidden drills (n = 10 each).
  
  
  RESULTS
  Simulated canals coronally enlarged with Gates-Glidden drills required a significantly longer removal time than other groups of identical apical size (p < 0.05). When groups with similar coronal enlargement were compared, those apically prepared to 35/06 required a significantly longer removal time than those prepared to 25/04 (p < 0.05). Coronally enlarged incisors also required a significantly longer removal time than those without coronal enlargement (p < 0.05).
  
  
  CONCLUSIONS
  Canals with a larger diameter and/or taper required more time for the removal of Thermafil Plus plastic carriers.
authors.affiliation: Division of Cariology, Operative Dentistry and Endodontics, Department of Oral Health Science, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Hayakawa
authors.forename: Fumihito
authors.initials: F
authors.lastname: Tomita
authors.forename: Takashi
authors.initials: T
authors.lastname: Okiji
mesh_terms: D003762:Dental Instruments; D003786:Dental Pulp Cavity / Q000033:anatomy & histology*; D020878:Device Removal / Q000295:instrumentation*; D004337:Drug Carriers; D006801:Humans; D007180:Incisor; D019233:Retreatment; D012387:Root Canal Filling Materials; D018915:Root Canal Preparation / Q000295:instrumentation*; D013997:Time Factors
chemical_list: D004337:Drug Carriers; D012387:Root Canal Filling Materials