title: Time-dependent properties of human root dentin.
abstract: OBJECTIVE
  The aim of this study was to investigate the creep, stress relaxation and strain rate behavior of human root dentin under compressive loading.
  
  
  METHODS
  Cylindrical root dentin samples of 3.5mm outer diameter, 1.5mm internal canal diameter and 6-10mm long were prepared from freshly extracted teeth. The samples were tested in a closed-loop servohydraulic testing machine at constant load or displacement, and varied strain rate. In vivo strain rates were estimated using strain gauges bonded to human teeth.
  
  
  RESULTS
  A family of creep curves, determined at different loads within dentin's elastic region, was found to be consistent with a material having linear viscoelastic behavior. A positive correlation (r(2)=0.79, P<0.001) was found between creep rate and stress. Young's modulus (E) was found to be a function of the strain rate with rates of loading in the range 10-500,000Ns(-1). Loading at constant displacement showed stress to be a decreasing function of time (i.e. stress relaxation).
  
  
  CONCLUSIONS
  Dentin showed linear-viscoelastic behavior under various conditions of compressive loading. Time dependent properties of dentin should be taken into account in restorative dentistry.
authors.affiliation: Department of Operative Dentistry, Mahidol University, Bangkok, Thailand.
authors.forename: Jeeraphat
authors.initials: J
authors.lastname: Jantarat
authors.forename: Joseph E A
authors.initials: JE
authors.lastname: Palamara
authors.forename: Cecylia
authors.initials: C
authors.lastname: Lindner
authors.forename: Harold H
authors.initials: HH
authors.lastname: Messer
mesh_terms: D000465:Algorithms; D001696:Biomechanical Phenomena; D001732:Bite Force; D002182:Candy; D003799:Dental Stress Analysis / Q000295:instrumentation; D003804:Dentin / Q000502:physiology*; D004548:Elasticity; D006801:Humans; D008409:Mastication / Q000502:physiology; D009754:Nuts; D010232:Paraffin / Q000737:chemistry; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013997:Time Factors; D014092:Tooth Root / Q000502:physiology*; D014783:Viscosity; D016474:Weight-Bearing
chemical_list: D010232:Paraffin