title: Dimensional accuracy of dental casts: influence of tray material, impression material, and time.
abstract: OBJECTIVE
  This study evaluated the influence on dimensional accuracy of dental casts made with different types of trays and impression materials and poured at different and multiple times.
  
  
  METHODS
  Two types of stock trays (plastic stock tray, perforated metal stock tray) and 4 types of custom tray materials (autopolymerizing acrylic resin, thermoplastic resin, and 2 types of light-polymerized acrylic resins) were used with 2 types of impression materials (addition polymerizing silicone and polyether), to make impressions of a metal master model. Each tray and impression material was used to make 5 impressions. Casts were made by multiple pourings at 30 minutes, 6 hours, 24 hours, and 30 days after impression making. Using a measuring microscope, 12 distances were calculated based on measurements of 8 reference points. The absolute value of the difference of each measurement was calculated, as was the corresponding measurement on the master model. A Bayesian model using a simple noninformative prior was used to analyze these data.
  
  
  RESULTS
  Statistical differences within 6 microm were found only with thermoplastic resin tray material for addition silicone, and for thermoplastic resin tray material and 1 type of light-polymerized acrylic resin for polyether. Neither stock trays nor custom trays contributed to the differences in accuracy of the casts. All deviations in casts made with silicone impression material were within a clinically acceptable range. For the polyether, distortions occurred that were clinically unacceptable. Impressions made from polyether distorted over time. Silicone impression material has dimensional stability up to 30 days.
  
  
  CONCLUSIONS
  Accurate casts can be made with either stock trays or custom trays. An impression made from polyether should be poured only once and within 24 hours after impression making, because of the distortion of the material over time. Silicone impression material has better dimensional stability than polyether. .
authors.affiliation: Department of Restorative Dentistry, Indiana University School of Dentistry, Indianapolis, IN 46202, USA. taumtium@hotmail.com
authors.forename: Sudsukh
authors.initials: S
authors.lastname: Thongthammachat
authors.forename: B Keith
authors.initials: BK
authors.lastname: Moore
authors.forename: M Thomas
authors.initials: MT
authors.lastname: Barco
authors.forename: Suteera
authors.initials: S
authors.lastname: Hovijitra
authors.forename: David T
authors.initials: DT
authors.lastname: Brown
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Andres
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D000269:Adhesives / Q000737:chemistry; D000497:Alloys / Q000737:chemistry; D001499:Bayes Theorem; D002133:Calcium Sulfate / Q000737:chemistry; D003734:Dental Casting Investment / Q000737:chemistry; D003735:Dental Casting Technique; D003760:Dental Impression Materials / Q000737:chemistry*; D003761:Dental Impression Technique / Q000295:instrumentation*; D004867:Equipment Design; D004987:Ethers / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D003765:Models, Dental; D010969:Plastics / Q000737:chemistry; D012826:Silicone Elastomers / Q000737:chemistry; D013223:Statistics as Topic; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry; D013997:Time Factors
chemical_list: D000180:Acrylic Resins; D000269:Adhesives; D000497:Alloys; D003734:Dental Casting Investment; D003760:Dental Impression Materials; D004987:Ethers; C096535:Permadyne Premier; D010969:Plastics; D012826:Silicone Elastomers; D013501:Surface-Active Agents; D002133:Calcium Sulfate