title: Instrument separation analysis of multi-used ProTaper Universal rotary system during root canal therapy.
abstract: BACKGROUND
  The purpose of this study was to identify the influential factors responsible for clinical instrument separation of reused ProTaper Universal rotary instruments (Dentsply Maillefer, Ballaigues, Switzerland).
  
  
  METHODS
  Six thousand one hundred fifty-four root canals in 2,654 teeth were prepared using ProTaper Universal files in endodontic clinics. Separation incidence was determined based on the number of treated teeth or canals. Data were collected including the size of fractured instrument, the length and location of a broken segment within the root canal, and the curvature of canal. The chi-square test and independent samples t test were used to determine the statistical significance.
  
  
  RESULTS
  The overall instrument separation incidences were 2.6% according to the number of teeth and 1.1% according to the canal number, respectively. Separation incidences according to the number of teeth or canals were significantly higher (P < .05) in molars than those in premolars or anterior teeth. Because of its largest diameter, F3 file presented the highest separation incidence according to the number of teeth (1.0%) or canals (0.4%); 47.5% instrument separation of mandibular molars and 61.5% instrument separation of maxillary molars happened in the mesiobuccal canals. Moreover, 91.4% fragments were located in the apical third of root canals, and 54.2% instrument separation occurred in severely curved canals. There was a significant difference (P < .05) in the mean fracture length between shaping (2.42 ± 0.73 mm) and finishing files (3.32 ± 0.73 mm).
  
  
  CONCLUSIONS
  Separation incidence according to the canal number is more reliable than that according to the number of teeth because of the variable canal number in different teeth. The tooth type, rotary file size, canal location, and anatomy were correlated with the instrument separation of reused ProTaper Universal files.
authors.affiliation: Endodontic Department, School of Stomatology, Nanjing Medical University, Jiangsu, China.
authors.forename: Jintao
authors.initials: J
authors.lastname: Wu
authors.forename: Gang
authors.initials: G
authors.lastname: Lei
authors.forename: Ming
authors.initials: M
authors.lastname: Yan
authors.forename: Yan
authors.initials: Y
authors.lastname: Yu
authors.forename: Jinhua
authors.initials: J
authors.lastname: Yu
authors.forename: Guangdong
authors.initials: G
authors.lastname: Zhang
mesh_terms: D001641:Bicuspid / Q000473:pathology; D003722:Dental Alloys / Q000737:chemistry*; D003786:Dental Pulp Cavity / Q000473:pathology; D004492:Edetic Acid / Q000737:chemistry; D004867:Equipment Design; D019544:Equipment Failure Analysis; D017743:Equipment Reuse; D005547:Foreign Bodies / Q000209:etiology; D006801:Humans; D008855:Microscopy, Electron, Scanning; D008963:Molar / Q000473:pathology; D009532:Nickel / Q000737:chemistry*; D016300:Radiography, Bitewing; D012388:Root Canal Irrigants / Q000627:therapeutic use; D018915:Root Canal Preparation / Q000295:instrumentation* / Q000379:methods; D012390:Root Canal Therapy / Q000295:instrumentation* / Q000379:methods; D012399:Rotation; D012973:Sodium Hypochlorite / Q000627:therapeutic use; D013314:Stress, Mechanical; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*; D019227:Tooth Apex / Q000473:pathology; D019415:Torque
chemical_list: D003722:Dental Alloys; D012388:Root Canal Irrigants; C040654:titanium nickelide; D009532:Nickel; D004492:Edetic Acid; D014025:Titanium; D012973:Sodium Hypochlorite