title: Effect of storage time on the viscoelastic properties of elastomeric impression materials.
abstract: OBJECTIVE
  The aim of this study was to evaluate creep and viscoelastic properties of dental impression materials after different storage times.
  
  
  METHODS
  Six commercially available impression materials (one polyether and five silicones) were tested after being stored for 30 min to 2 weeks under both static and dynamic testing. Shear and Young's moduli, dynamic viscosity, loss tangent and other viscoelastic parameters were calculated. Four of the materials were tested 1 h after setting under creep for three hours and recovery was recorder for 50 h.
  
  
  RESULTS
  The tested materials showed differences among them, while storage time had significant influence on their properties. Young's modulus E ranged from 1.81 to 12.99 MPa with the polyether material being the stiffest. All of the materials showed linear viscoelastic behavior exhibiting permanent deformation after 50h of creep recovery.
  
  
  CONCLUSIONS
  As storage time affects the materials' properties, pouring time should be limited in the first 48 h after impression.
authors: Department of Biomaterials, School of Dentistry, University of Athens, Greece. deminho@gmail.com
authors: Dimitris
authors: D
authors: Papadogiannis
authors: Roderic
authors: R
authors: Lakes
authors: George
authors: G
authors: Palaghias
authors: Yiannis
authors: Y
authors: Papadogiannis