title: Influence of instrument taper on the resistance to fracture of endodontically treated roots.
abstract: OBJECTIVE
  The aim was to compare the force required to fracture uninstrumented and instrumented canines and to investigate the root-reinforcing capability of AH Plus sealer.
  
  
  METHODS
  In groups 1-3 (n = 24) canals were instrumented with either GT files, FlexMaster, or stainless steel hand instruments. Twelve teeth from each group were obturated with lateral compaction using gutta-percha and AH Plus. Group 4 (n = 12) acted as uninstrumented controls. The force required to fracture the roots was measured. ANOVA, Scheffé, and t test were used for statistical analysis.
  
  
  RESULTS
  The intact roots were significantly stronger than all groups with instrumented and unobturated roots (P < .05). Roots enlarged with GT files were significantly weaker (P < .05) than those instrumented with FlexMaster or hand instruments. Between the obturated and unobturated roots there were no significant differences (P > .05).
  
  
  CONCLUSIONS
  The roots were significantly weakened by the preparation with greater taper instruments. An obturation with AH Plus did not increase the fracture resistance.
authors.affiliation: Department of Operative Dentistry, University of Münster, Münster, Germany.
authors.forename: Tannaz
authors.initials: T
authors.lastname: Zandbiglari
authors.forename: Hendrik
authors.initials: H
authors.lastname: Davids
authors.forename: Edgar
authors.initials: E
authors.lastname: Schäfer
mesh_terms: D003481:Cuspid; D003722:Dental Alloys; D003762:Dental Instruments; D003799:Dental Stress Analysis; D004853:Epoxy Resins; D004867:Equipment Design; D006171:Gutta-Percha; D006801:Humans; D009532:Nickel; D012387:Root Canal Filling Materials; D018915:Root Canal Preparation / Q000009:adverse effects / Q000295:instrumentation*; D013193:Stainless Steel; D014025:Titanium; D014082:Tooth Fractures / Q000209:etiology / Q000517:prevention & control*; D014092:Tooth Root / Q000293:injuries
chemical_list: D003722:Dental Alloys; D004853:Epoxy Resins; D012387:Root Canal Filling Materials; C534916:epoxy resin-based root canal sealer; C040654:titanium nickelide; D013193:Stainless Steel; D009532:Nickel; D006171:Gutta-Percha; D014025:Titanium