title: A clinical study comparing the three-dimensional accuracy of a working die generated from two dual-arch trays and a complete-arch custom tray.
abstract: BACKGROUND
  Dual-arch trays are often used by the dentists to make crown impressions of opposing quadrants simultaneously. Metal and plastic trays are available, but little is known about the accuracy of the impressions and resultant working dies.
  
  
  OBJECTIVE
  The purpose of this study was to conduct a clinical trial to compare the accuracy of gypsum working dies made from impressions with metal dual-arch, plastic dual-arch, and complete-arch custom trays.
  
  
  METHODS
  Eight patients requiring a posterior single tooth implant restoration were selected on the basis of inclusion and exclusion criteria. A customized abutment was measured in 3 dimensions (buccolingual, mesiodistal, and occlusogingival) by use of a measuring microscope. Three polyvinyl siloxane impressions were made of the abutment with a complete-arch custom tray, a plastic, and a metal dual-arch tray. Each impression was poured with type IV improved dental die stone. The diameter (buccolingual and mesiodistal), from gingivoaxial to gingivoaxial point angle, and height (occlusogingival), gingivoaxial to occlusoaxial point angle of the abutment standard was determined by measuring each dimension several times to obtain a mean. These 3 mean values served as the controls and were compared with the same measurements of the gypsum dies generated by the 3 different impression techniques. The patient was asked to rank the 3 impressions in order of overall comfort. A multivariate repeated measures single factor ANOVA was used in the statistical analysis (alpha=.05). When main effects were significant, a pairwise comparison of mean values was conducted with Bonferonni adjustment for multiple comparisons.
  
  
  RESULTS
  There were no significant differences in die accuracy among the 3 trays for the mesiodistal (3.507 mm) and occlusogingival (3.584 mm) dimensions of the implant abutment. Dies were smaller than the standard for these 2 dimensions and larger in the buccolingual dimension. There was a significant difference in accuracy between the metal and plastic dual-arch trays. The dies produced from the metal dual-arch tray were 20 microm larger than the abutment standard compared with 3 microm larger for the plastic tray. The occlusogingival dimension of the working dies was 30 to 40 microm shorter than the implant abutment. Seven of the 8 patients ranked the plastic dual-arch impression as the most comfortable and the complete-arch custom tray as the least comfortable.
  
  
  CONCLUSIONS
  Within the limitations of this study, the dimensions of working dies from a custom tray impression did not differ significantly from those created with dual arch trays. However, working dies from a plastic dual-arch tray were more accurate buccolingually than those from metal dual-arch trays.
authors.affiliation: School of Dentistry, Department of Restorative Dentistry, University of Washington, Seattle, WA 98195-7456, USA.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Ceyhan
authors.forename: Glen H
authors.initials: GH
authors.lastname: Johnson
authors.forename: Xavier
authors.initials: X
authors.lastname: Lepe
authors.forename: Keith M
authors.initials: KM
authors.lastname: Phillips
mesh_terms: D003442:Crowns; D000044:Dental Abutments; D015921:Dental Implants; D003761:Dental Impression Technique / Q000295:instrumentation*; D006801:Humans; D008670:Metals; D003765:Models, Dental; D017060:Patient Satisfaction; D010969:Plastics; D015203:Reproducibility of Results
chemical_list: D015921:Dental Implants; D008670:Metals; D010969:Plastics