title: Accuracy of open tray implant impressions: an in vitro comparison of stock versus custom trays.
abstract: BACKGROUND
  The accuracy of an implant fixture-level impression is affected by the type of impression tray used.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to investigate the accuracy of open tray implant impressions comparing polycarbonate stock impression trays and rigid custom-made impression trays to make implant fixture-level impressions.
  
  
  METHODS
  Gold cylinder pairs, splinted by gold bars (reference frameworks) were constructed on an aluminum typodont. Polyether impressions were made of 2 pairs of Brånemark 3.75-mm diameter fixtures mounted in an aluminium typodont, with 3 stock impression trays, 3 close-fit custom trays, and 3 spaced custom impression trays, by use of an open tray technique. The casts produced were assessed for accuracy by attaching the reference frameworks with alternate single screws and measuring the vertical fit discrepancy of these reference frameworks to the analogs within the working cast using a traveling microscope. Comparison of gap dimensions by tray type was performed with a nonparametric Kruskal-Wallis analysis of variance (ANOVA) followed by pair-wise Mann-Whitney U tests. To adjust for multiple comparisons in the post-ANOVA contrasts (P<.02). Comparison of gap dimensions between anterior and posterior regions were performed with Mann-Whitney U tests (P <.05).
  
  
  RESULTS
  The results showed that the mean fit accuracy, as measured by vertical fit discrepancy, of casts from the stock trays (23 +/- 20 microm) were statistically significantly less (P<.001) than the spaced custom trays (12 +/- 10 microm) or close fit custom trays (11 +/- 10 microm). The difference in median gap size for analogs with a 20-mm separation was 10 microm.
  
  
  CONCLUSIONS
  Within the limits of this in vitro study, rigid custom trays produced significantly more accurate impressions than the polycarbonate stock trays. The stock trays used in this study could not produce accurate impressions consistently. For analogs with a 20-mm separation, there was a difference in medians of 10 microm in accuracy between the stock and custom trays.
authors.affiliation: Guys Hospital, London, England. jason@molars.com
authors.forename: Jason
authors.initials: J
authors.lastname: Burns
authors.forename: Richard
authors.initials: R
authors.lastname: Palmer
authors.forename: Leslie
authors.initials: L
authors.lastname: Howe
authors.forename: Ron
authors.initials: R
authors.lastname: Wilson
mesh_terms: D000704:Analysis of Variance; D002133:Calcium Sulfate / Q000737:chemistry; D000044:Dental Abutments; D015921:Dental Implants; D003760:Dental Impression Materials / Q000737:chemistry; D003761:Dental Impression Technique / Q000295:instrumentation*; D003764:Dental Materials / Q000737:chemistry; D004867:Equipment Design; D006801:Humans; D016555:Matched-Pair Analysis; D008422:Materials Testing; D003765:Models, Dental; D018583:Pliability; D011076:Polycarboxylate Cement / Q000737:chemistry; D012117:Resins, Synthetic / Q000737:chemistry; D018709:Statistics, Nonparametric; D013499:Surface Properties
chemical_list: D015921:Dental Implants; D003760:Dental Impression Materials; D003764:Dental Materials; C022821:Impregum; D011076:Polycarboxylate Cement; D012117:Resins, Synthetic; C005506:polycarbonate; D002133:Calcium Sulfate