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 dentinʹs elastic region, was found to be consistent with a material having linear viscoelastic behavior. A positive correlation (r2=0.79, P<0.001) was found between creep rate and stress. Youngʹs 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.