title: Distortion of disposable plastic stock trays when used with putty vinyl polysiloxane impression materials.
abstract: BACKGROUND
  Impressions are made using high-viscosity putty vinyl polysiloxane impression materials in conjunction with disposable plastic stock trays. The impression materials have been shown to be dimensionally stable. However, it remains unclear if the disposable plastic stock trays are rigid enough to resist deformation thus yielding potentially unreliable results.
  
  
  OBJECTIVE
  This study evaluated the rigidity and ability to resist deformation of 6 commercially available disposable plastic stock trays and 1 metal stock tray when used in conjunction with a high-viscosity vinyl polysiloxane impression material.
  
  
  METHODS
  Ten impressions were made with 1 putty vinyl polysiloxane material (Reprosil Putty) using each of the 6 tested disposable plastic stock trays, Sani-Trays (perforated), Sani-Trays (nonperforated), COE Disposable Spacer Tray (perforated), COE Disposable Spacer Tray (nonperforated), Bosworth Tray-Aways (perforated), Track-it Trays (perforated), and 1 metal stock tray (nonperforated), Cadco Dental Products, as a control on a mandibular plastic model. The dimensions of the tray in cross section at the mandibular right first molar area were measured before, during, and after the impression procedures with an electronic digital caliper. The cross-arch dimensions of the tray were measured at similar intervals. One examiner made all measurements and each measurement was repeatable within +/-0.01 mm. A split plot repeated measures analysis of variance (ANOVA) was performed and 2-sided P -values were calculated (alpha=.05).
  
  
  RESULTS
  The results indicated that the disposable plastic trays tested were not sufficiently rigid to resist deformation when used with very high-viscosity putty material. Metal stock trays showed significantly less change in cross-arch dimension than plastic trays (F(1.68)=11.25, P =.001). Metal stock trays also showed significantly less change in cross-sectional arch dimension than plastic trays (F(1.68)=15.15, P<.001).
  
  
  CONCLUSIONS
  When disposable plastic stock trays were tested in conjunction with very high-viscosity impression materials there was distortion of the tray both across the arch and in cross section.
authors.affiliation: University of Southern California School of Dentistry, Los Angeles, California, USA.
authors.forename: George C
authors.initials: GC
authors.lastname: Cho
authors.forename: Winston W L
authors.initials: WW
authors.lastname: Chee
mesh_terms: D003760:Dental Impression Materials; D003761:Dental Impression Technique / Q000295:instrumentation*; D003762:Dental Instruments; D004867:Equipment Design; D010969:Plastics; D011145:Polyvinyls; D012833:Siloxanes; D014783:Viscosity
chemical_list: D003760:Dental Impression Materials; D010969:Plastics; D011145:Polyvinyls; D012833:Siloxanes; C034183:vinyl polysiloxane