title: Influence of prolonged setting time on permanent deformation of elastomeric impression materials.
abstract: BACKGROUND
  Upon removal, tear forces occur in various areas of an impression. As a result, thin sulcus details may be permanently deformed, affecting the impression's accuracy.
  
  
  OBJECTIVE
  The purpose of this study was to investigate the effect of the chemistry and prolonged setting time on the permanent deformation of light-body impression materials after stretching.
  
  
  METHODS
  A dumbbell-shaped mold (2 mm x 4 mm x 75 mm) was used to prepare specimens (n=20) of 6 different impression materials (Affinis Light Body, Aquasil Ultra XLV, Express 2 Light Body Flow Quick, Flexitime Correct Flow, P2 Polyether Light, and Impregum Garant L DuoSoft). After water storage (35 degrees C), either for the manufacturer's suggested setting time or for 5 minutes, specimens were stretched by 80% using a universal testing machine at a crosshead speed of 200 mm/min. The permanent deformation (Deltal (%)) was determined after 2 hours of storage in ambient conditions. A 2-way ANOVA followed by a Games-Howell test was used to analyze the influence of material and storage time (alpha=.05).
  
  
  RESULTS
  Polyether materials showed a significantly higher permanent deformation (Deltal>4% to 5%) than vinyl polysiloxane materials (P<.05). Extending the manufacturer's suggested setting time resulted in clinically relevant improvements in elastic recovery for products with a polyether backbone only.
  
  
  CONCLUSIONS
  Increasing the setting time might be necessary for impression materials with a polyether backbone to improve elastic recovery.
authors.affiliation: Department of Prosthodontics, Justus Liebig University, Giessen, Germany. markus.balkenhol@dentist.med.uni-giessen.de <markus.balkenhol@dentist.med.uni-giessen.de>
authors.forename: Markus
authors.initials: M
authors.lastname: Balkenhol
authors.forename: Sylvia
authors.initials: S
authors.lastname: Haunschild
authors.forename: Christina
authors.initials: C
authors.lastname: Erbe
authors.forename: Bernd
authors.initials: B
authors.lastname: Wöstmann
mesh_terms: D003760:Dental Impression Materials / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D055119:Elastic Modulus; D004548:Elasticity; D020724:Elastomers / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D011145:Polyvinyls / Q000737:chemistry; D012117:Resins, Synthetic / Q000737:chemistry; D012833:Siloxanes / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D003760:Dental Impression Materials; D020724:Elastomers; C022821:Impregum; D011145:Polyvinyls; D012117:Resins, Synthetic; C510540:SENN polyvinylsiloxane-polyether hybrid; D012833:Siloxanes; C480691:aquasil; C034183:vinyl polysiloxane; D014867:Water