title: The influence of tray type and other variables on the palatal depth of casts made from irreversible hydrocolloid impressions.
abstract: BACKGROUND
  There are conflicting data regarding the effect of various factors on the palatal depth of casts made from irreversible hydrocolloid impressions.
  
  
  OBJECTIVE
  This study examined the influence of tray type, water temperature, pouring technique, and stone expansion on the palatal depth of casts.
  
  
  METHODS
  Irreversible hydrocolloid impressions were made of a model under simulated oral conditions. Palatal depth was measured relative to a reference plane with a microscope. The reference planes were standardized by subjecting the data to three 2-dimensional mathematic rotations. A 2-factor analysis of variance (alpha=.05) was used to determine whether differences existed among tray types and among palatal locations.
  
  
  RESULTS
  The palatal depth of the casts increased approximately 0.06 mm compared with the master model with all but 2 variables. Statistical testing revealed that increased depth was not attributable to water temperature (52 degrees F or 72 degrees F) or tray type (custom resin, perforated metal, metal rimlock, or rimlock with built-up palate). Custom resin tray impressions poured with a lower expansion stone and perforated tray impressions inverted onto a base made from the same mix of stone resulted in casts with palatal depths most similar to that of the master model (P<.001).
  
  
  CONCLUSIONS
  Casts with palatal contours of comparable accuracy were obtained with the use of a stock metal or customized tray and the use of differing water temperatures to mix the impression material.
authors.affiliation: Department of Prosthodontics, School of Dentistry, University of Washington, Seattle, WA 98195-7452, USA. hiker2@u.washington.edu
authors.forename: Richard P
authors.initials: RP
authors.lastname: Frank
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Thielke
authors.forename: Glen H
authors.initials: GH
authors.lastname: Johnson
mesh_terms: D000180:Acrylic Resins; D000464:Alginates / Q000737:chemistry* / Q000145:classification; D000704:Analysis of Variance; D002133:Calcium Sulfate / Q000737:chemistry; D003102:Colloids / Q000737:chemistry; D003722:Dental Alloys; D003734:Dental Casting Investment / Q000737:chemistry; D003760:Dental Impression Materials / Q000737:chemistry* / Q000145:classification; D003761:Dental Impression Technique / Q000295:instrumentation*; D004867:Equipment Design; D006801:Humans; D007576:Jaw, Edentulous, Partially / Q000473:pathology; D008853:Microscopy; D003765:Models, Dental; D010159:Palate / Q000033:anatomy & histology; D012117:Resins, Synthetic; D013223:Statistics as Topic; D013499:Surface Properties; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D000180:Acrylic Resins; D000464:Alginates; D003102:Colloids; D003722:Dental Alloys; D003734:Dental Casting Investment; D003760:Dental Impression Materials; D012117:Resins, Synthetic; D014867:Water; D002133:Calcium Sulfate