title: Residual Microstrain in Root Dentin after Canal Instrumentation Measured with Digital Moiré Interferometry.
abstract: BACKGROUND
  Residual microstrain influences the resistance to crack propagation in a biomaterial. This study evaluated the residual microstrain and microdefects formed in dentin after canal instrumentation in teeth maintained in hydrated and nonhydrated environments.
  
  
  METHODS
  Canals of 18 extracted human premolars with single-root canals were instrumented in accordance with 3 groups: the ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland) group: ProTaper Universal (S1, S2, F1, and F2) used in rotation, the WaveOne Primary (Dentsply Maillefer) group: the WaveOne (Primary) used in reciprocal motion, and the control group: hand files. Half the specimens (3/group) were maintained in deionized water (hydrated) and half in ambient relative humidity conditions (22°C, 55% RH) for 72 hours (nonhydrated). Customized high-sensitivity digital moiré interferometry was used to qualitatively evaluate pre- and postinstrumentation dentinal microstrain. Subsequently, specimens were examined for dentinal microdefects with micro-computed tomographic imaging and polarized light microscopy.
  
  
  RESULTS
  Digital moiré interferometry showed only minor changes in postinstrumentation microstrain in hydrated dentin in all groups, suggestive of a stress relaxation behavior. Nonhydrated dentin in all groups showed localized concentration of postinstrumentation microstrain, which appeared higher in the WaveOne group than in the other groups. No dentinal microdefects were detected by micro-computed tomographic imaging and polarized light microscopy in hydrated and nonhydrated specimens in all groups.
  
  
  CONCLUSIONS
  This study suggested that the biomechanical response of root dentin to instrumentation was influenced by hydration. Reciprocating, rotary, and hand instrumentation of well-hydrated roots did not cause an increase in residual microstrain or the formation of microdefects in root dentin.
authors.affiliation: Discipline of Endodontics/Dental Research Institute, Faculty of Dentistry, University of Toronto, Toronto, Canada.
authors.forename: Helena
authors.initials: H
authors.lastname: Lim
authors.affiliation: Discipline of Endodontics/Dental Research Institute, Faculty of Dentistry, University of Toronto, Toronto, Canada.
authors.forename: Fang-Chi
authors.initials: FC
authors.lastname: Li
authors.affiliation: Discipline of Endodontics/Dental Research Institute, Faculty of Dentistry, University of Toronto, Toronto, Canada.
authors.forename: Shimon
authors.initials: S
authors.lastname: Friedman
authors.affiliation: Discipline of Endodontics/Dental Research Institute, Faculty of Dentistry, University of Toronto, Toronto, Canada. Electronic address: anil.kishen@utoronto.ca.
authors.forename: Anil
authors.initials: A
authors.lastname: Kishen
mesh_terms: D001641:Bicuspid / Q000502:physiology; D003799:Dental Stress Analysis; D003804:Dentin / Q000502:physiology*; D006801:Humans; D007368:Interferometry; D012390:Root Canal Therapy / Q000009:adverse effects / Q000295:instrumentation; D013314:Stress, Mechanical; D014092:Tooth Root / Q000502:physiology*
keywords: Canal instrumentation; dentin dehydration; microdefects; moiré interferometry; residual microstrain