title: Working time of elastomeric impression materials: relevance of rheological tests.
abstract: OBJECTIVE
  To study possible relationships between rheological parameters of elastomeric impression materials and their dimensional accuracy at different stages during setting within the manufacturers' recommended working time.
  
  
  METHODS
  Four chemically different impression material-types were tested. Impressions were taken of a master cone at 30-second intervals after mixing and up to 30 seconds beyond the recommended working time. Impression accuracy (deltad) was determined as the dimensional deviation of stone dies from the master cone. The phase angle delta(t) and storage modulus G'(t) were measured and the working time determined according to ISO 4823. Three operators assessed the latest point in time for uncompromised impression taking. Correlation analysis was performed using Spearman's Rho (P = 0.05).
  
  
  RESULTS
  For most materials investigated, deltad(t) was constant within the manufacturers' recommended working time whereas delta(t) and G'(t) changed significantly. There was no correlation (P > 0.05) between deltad(t) versus delta(t) and G'(t), respectively. When determined according to ISO 4823, working time was longer than operator-assessed working time for all materials investigated.
authors.affiliation: Department of Prosthetic Dentistry, School of Dental Medicine, Justus-Liebig-University, Giessen, Germany. markus.balkenhol@dentist.med.uni-giessen.de
authors.forename: Markus
authors.initials: M
authors.lastname: Balkenhol
authors.forename: Masafumi
authors.initials: M
authors.lastname: Kanehira
authors.forename: Werner J
authors.initials: WJ
authors.lastname: Finger
authors.forename: Bernd
authors.initials: B
authors.lastname: Wöstmann
mesh_terms: D003760:Dental Impression Materials / Q000737:chemistry*; D003761:Dental Impression Technique / Q000295:instrumentation / Q000706:statistics & numerical data; D004548:Elasticity; D020724:Elastomers / Q000737:chemistry*; D004987:Ethers / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D003765:Models, Dental; D044367:Phase Transition; D011145:Polyvinyls / Q000737:chemistry; D012117:Resins, Synthetic / Q000737:chemistry; D012212:Rheology; D012833:Siloxanes / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors
chemical_list: D003760:Dental Impression Materials; D020724:Elastomers; D004987:Ethers; C022821:Impregum; D011145:Polyvinyls; D012117:Resins, Synthetic; D012833:Siloxanes; C034183:vinyl polysiloxane