title: Measurement of strain on tooth roots during post removal with the Eggler post remover.
abstract: OBJECTIVE
  The aim was to measure root surface strains in teeth when removing cast post/cores with the Eggler post remover.
  
  
  METHODS
  Two groups of 10 teeth each were tested: group 1 had 1 mm thickness of dentine coronally, and group 2 had 2 mm thickness of dentine. After root filling, 10 mm long cast post/cores were constructed and cemented with zinc phosphate cement, and strain gauges were applied to the roots. The post/cores were removed with the Eggler post remover whilst strain measurements were being recorded. Posts were removed twice: initially along the long axis of the tooth and then at a 10 degrees angle to the long axis. Comparisons between groups 1 and 2 were analysed statistically with the Mann-Whitney U-test whilst strains within each group were analysed with the Wilcoxon Signed Rank test at the 95% level of confidence.
  
  
  RESULTS
  There was no significant difference in the strains measured between groups 1 and 2, and no significant difference within each group when removing posts along the long axis of the tooth and at a 10 degrees angle. Three teeth in group 1 and one tooth in group 2 fractured when removing posts at the 10 degrees angle. Three fractures were small slivers of dentine at the point where the Eggler's repeller arms contacted the tooth mesially and distally, whilst one tooth (from group 1) fractured obliquely.
  
  
  CONCLUSIONS
  Post removal with the Eggler device is a relatively safe procedure but care must be taken when there is a possibility of pulling the post out in a nonaxial direction or when less than 1 mm of dentine surrounds the apical end of the post.
authors.affiliation: School of Dental Science, University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: T V
authors.initials: TV
authors.lastname: Castrisos
authors.forename: J E A
authors.initials: JE
authors.lastname: Palamara
authors.forename: P V
authors.initials: PV
authors.lastname: Abbott
mesh_terms: D002484:Cementation; D016001:Confidence Intervals; D017005:Dental Debonding / Q000295:instrumentation*; D017267:Dental Prosthesis Design; D003804:Dentin / Q000502:physiology; D004867:Equipment Design; D006171:Gutta-Percha / Q000627:therapeutic use; D006801:Humans; D011176:Post and Core Technique / Q000295:instrumentation; D012387:Root Canal Filling Materials / Q000627:therapeutic use; D018915:Root Canal Preparation; D018709:Statistics, Nonparametric; D013314:Stress, Mechanical; D013499:Surface Properties; D014082:Tooth Fractures / Q000503:physiopathology; D014092:Tooth Root / Q000293:injuries / Q000502:physiology*; D015036:Zinc Phosphate Cement / Q000737:chemistry
chemical_list: D012387:Root Canal Filling Materials; D015036:Zinc Phosphate Cement; D006171:Gutta-Percha