title: Dimensional accuracy of a new polyether impression material.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the dimensional accuracy of stone dies produced from standardized impressions with 1 new and 1 conventional polyether impression material and a polyvinyl siloxane reference material.
  
  
  METHODS
  Impressions with the polyether materials P2 and Impregum and with the polyvinyl siloxane Flexitime were produced at 23 degrees C or 37 degrees C from a truncated steel cone in cylindrical steel trays giving 4-mm impression layer thickness at the prominence line. Stone dies were poured after 1 or 24 hours of storage at ambient atmosphere. Additional impressions were stored at different relative humidity levels (0%, 33%, 50%, 75%, or 100%) for 24 hours prior to die pouring. The accuracy of the stone dies was determined as axial discrepancy between a steel ring, which fit perfectly on the steel die and the occlusal die surface. The base-diameter deviation (deltad) was calculated.
  
  
  RESULTS
  After 1 hour, a similar increase in deltad was noticed for impression materials when dies were poured at impression temperature. Impressions made at 37 degrees C exhibited significantly higher deltad than at 23 degrees C. Light-bodied P2 showed the highest deltad increase when dies were poured after 24 hours. Flexitime showed moderate deltad differences at the 2 pouring times. The deltad of dies made from polyether materials decreased significantly with increasing humidity, whereas polyvinyl siloxane was not adversely affected.
  
  
  CONCLUSIONS
  The dimensional accuracy of P2 is comparable to that of the conventional polyether impression material after short-term storage. Polyethers may absorb water, significantly compromising die accuracy upon storage at high humidity.
authors.affiliation: Division of Operative Dentistry, Department of Restorative Dentistry, Tohoku University Graduate School of Dentistry, Japan.
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Endo
authors.forename: Werner J
authors.initials: WJ
authors.lastname: Finger
mesh_terms: D000042:Absorption; D002133:Calcium Sulfate / Q000737:chemistry; D003760:Dental Impression Materials / Q000737:chemistry*; D003761:Dental Impression Technique / Q000295:instrumentation; D003764:Dental Materials / Q000737:chemistry; D004987:Ethers / Q000737:chemistry*; D006801:Humans; D006813:Humidity; D008422:Materials Testing; D003765:Models, Dental; D011145:Polyvinyls / Q000737:chemistry; D012117:Resins, Synthetic / Q000737:chemistry; D012833:Siloxanes / Q000737:chemistry; D013232:Steel / Q000737:chemistry; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors
chemical_list: D003760:Dental Impression Materials; D003764:Dental Materials; D004987:Ethers; C022821:Impregum; D011145:Polyvinyls; D012117:Resins, Synthetic; D012833:Siloxanes; C034183:vinyl polysiloxane; D013232:Steel; D002133:Calcium Sulfate