title: Rheological properties of vinyl polysiloxane impression pastes.
abstract: OBJECTIVE
  Some vinyl polysiloxane impression (VPS) materials are claimed to be 'thixotropic' so that they will have 'non-drip' properties and not flow off an impression tray during insertion of the material into the mouth. This work was carried out to investigate rheological properties of VPS materials by determination of their flow properties under different experimental conditions relevant to their dental application.
  
  
  METHODS
  The rheological characteristics of each component paste of two low viscosity VPS materials were assessed by a Dynamic Stress Rheometer using cone and plate geometry.
  
  
  RESULTS
  Both pastes of one product (Imprint II) showed a yield stress of around 40 Pa in addition to some degree of true thixotropy. In contrast, both Examix pastes had no yield stress value, but the catalyst paste was markedly thixotropic, as shown by a drop in viscosity as a result of application of shear force over time. Both products had thixotropic properties. The Imprint II in addition showed a yield stress that would also contribute to the 'non-drip' properties.
  
  
  CONCLUSIONS
  Combination of yield stress and thixotropy will prevent the undesirable drip of the materials once it has been injected around the tooth preparation until the impression tray is loaded and seated. After seating the tray, a thixotropic material will not flow.
authors.affiliation: Department of Restorative Sciences, College of Dental Medicine, Nova Southeastern University, Fort Lauderdale, FL, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Martinez
authors.forename: E C
authors.initials: EC
authors.lastname: Combe
authors.forename: I J
authors.initials: IJ
authors.lastname: Pesun
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003760:Dental Impression Materials / Q000737:chemistry*; D008422:Materials Testing; D011145:Polyvinyls / Q000737:chemistry*; D012212:Rheology; D012833:Siloxanes / Q000737:chemistry*; D014783:Viscosity
chemical_list: D003760:Dental Impression Materials; D011145:Polyvinyls; D012833:Siloxanes; C034183:vinyl polysiloxane