title: A survey of interfacial forces used during endosonic instrumentation of root canals.
abstract: OBJECTIVE
  The aim of this in-vitro study was to measure interfacial forces acting between root canal dentine and ultrasonic files during endosonic instrumentation.
  
  
  METHODS
  Single-rooted teeth were mounted on a cantilevered aluminium beam to which two pairs of single element strain gauges were joined in a half-bridge configuration mounted at right angles to each other. The strain gauges were connected to an analogue-to-digital converter fitted in a microcomputer via a conditioning amplifier. This enabled strains to be recorded as a function of interfacial forces over a period of time. Twenty operators instrumented root canals using sizes 15, 20 and 25 ultrasonically energized K-type files. The lateral forces generated were calculated.
  
  
  RESULTS
  The mean interfacial forces used varied widely between operators and files, ranging from 18 g to 149 g, but there was a consistency in the relative magnitude for each operator. The average force used by the operators increased with file size; the differences between file sizes were significant (P < 0.05).
  
  
  CONCLUSIONS
  The range of forces measured is broader than previously reported and may have a bearing on possible uncontrolled dentine removal, even during ultrasonically activated irrigation.
authors: Eastman Dental Institute for Oral Health Care Sciences, University College London, London, 256 Gray's Inn Road, London, WC1X 8LD, England.
authors: J D
authors: JD
authors: Regan
authors: M
authors: M
authors: Sherriff
authors: N
authors: N
authors: Meredith
authors: K
authors: K
authors: Gulabivala
mesh_terms: D000703:Analog-Digital Conversion; D000704:Analysis of Variance; D003786:Dental Pulp Cavity / Q000503:physiopathology*; D003804:Dentin / Q000503:physiopathology; D004867:Equipment Design; D006801:Humans; D008838:Microcomputers; D018915:Root Canal Preparation / Q000295:instrumentation* / Q000379:methods; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D014159:Transducers; D014464:Ultrasonic Therapy / Q000295:instrumentation* / Q000379:methods