title: Residual filling material in dentinal tubules after gutta-percha removal observed with scanning electron microscopy.
abstract: BACKGROUND
  In cases of failed root canal treatment, endodontic retreatment of the root canal system is necessary. The present study aimed to assess variation in the incidence and depth of residual filling material in dentinal tubules after gutta-percha removal with H-files, the ProTaper Universal System (Dentsply Maillefer, Ballaigues, Switzerland), and the SybronEndo K3 System (SybronEndo Corporation, Orange, CA).
  
  
  METHODS
  Forty human mandibular premolars with single straight root canals were prepared with K-files (up to size 40) using the step-back technique and filled by cold lateral condensation with gutta-percha and AH Plus sealers (Dentsply DeTrey, Konstanz, Germany). After 1 year, the 40 teeth were divided into one control group and 3 retreatment groups (n = 10 each). Gutta-percha was removed using H-files, the ProTaper Universal System, or the SybronEndo K3 System. The teeth were sectioned, and the incidence and depth of residual filling material in the dentinal tubules were measured under scanning electron microscopy.
  
  
  RESULTS
  The depth of filling material in the dentinal tubules did not differ significantly among groups (P > .05). Residual filling material was present in significantly more dentinal tubules in the ProTaper (P = .043) and K3 groups (P = .001) than in the H-file and control groups.
  
  
  CONCLUSIONS
  The ProTaper Universal System and the SybronEndo K3 System left filling material in a greater proportion of dentinal tubules than did H-files.
authors.affiliation: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu, China.
authors.forename: Li-li
authors.initials: LL
authors.lastname: Xu
authors.forename: Lan
authors.initials: L
authors.lastname: Zhang
authors.forename: Xue-dong
authors.initials: XD
authors.lastname: Zhou
authors.forename: Rui
authors.initials: R
authors.lastname: Wang
authors.forename: Yan-han
authors.initials: YH
authors.lastname: Deng
authors.forename: Ding-ming
authors.initials: DM
authors.lastname: Huang
mesh_terms: D002725:Chloroform / Q000737:chemistry; D003804:Dentin / Q000648:ultrastructure*; D004492:Edetic Acid / Q000737:chemistry; D004853:Epoxy Resins / Q000737:chemistry; D006171:Gutta-Percha / Q000737:chemistry*; D006801:Humans; D006813:Humidity; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D019233:Retreatment; D012387:Root Canal Filling Materials / Q000737:chemistry*; D012388:Root Canal Irrigants / Q000737:chemistry; D018915:Root Canal Preparation / Q000295:instrumentation / Q000379:methods; D012973:Sodium Hypochlorite / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013696:Temperature; D013997:Time Factors
chemical_list: D004853:Epoxy Resins; D012387:Root Canal Filling Materials; D012388:Root Canal Irrigants; D012997:Solvents; C534916:epoxy resin-based root canal sealer; D002725:Chloroform; D006171:Gutta-Percha; D004492:Edetic Acid; D012973:Sodium Hypochlorite