Time-dependent properties of human root dentin

Objectives: 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 3.5 mm outer diameter, 1.5 mm internal canal diameter and 6-10 mm 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 10-500.000 Ns(-1). Loading at constant displacement showed stress to be a decreasing function of time (i.e. stress relaxation). Significance: Dentin showed linear-viscoelastic behavior under various conditions of compressive loading. Time dependent properties of dentin should be taken into account in restorative dentistry. (C) 2002 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved.