title: An accuracy evaluation of four removable die systems.
abstract: BACKGROUND
  The advent of implant dentistry has redefined the need for accuracy of working cast models. Die stone expansion and errors introduced by removable die casts may exceed the accuracy required for the passive fit of implant prostheses.
  
  
  OBJECTIVE
  Several removable die systems claim improved accuracy because of their design and/or technical advancements. This study evaluated the 3-dimensional accuracy of 4 removable die systems. All 4 systems tested use either 1 or 2 pins as the repositioning device.
  
  
  METHODS
  Four removable die systems were evaluated (Belle de St. Claire, Pindex, DVA, and conventional brass dowel system). Master model impressions were made with polyvinyl siloxane material and were later cast with type IV die stone material. Comparative dimensional analysis between the master model and the solid and sectioned casts was made by placing the cast in a standardized position and fabricating an individual custom base for each cast. Landmarks were measured with a traveling microscope, and by mathematically rotating the casts. Discrepancies beyond that of stone expansion or residual stress release at the time of die separation were due to the inability to precisely reposition the removable die of the sectioned cast. Data were analyzed with multivariate analysis of variance and paired t tests at alpha = .05 (n = 10).
  
  
  RESULTS
  Significant differences were found among die systems tested (P = .005). When sectioned dies were compared with the master model, the accuracy of all 4 die systems was within 0.055 mm of the master model. Once sectioned, the Pindex system had the least linear expansion in the y dimension, and the brass dowel system demonstrated the least reseating discrepancy in the z (occlusogingival) dimension.
  
  
  CONCLUSIONS
  All 4 die systems provided a similar degree of dimensional accuracy, although Pindex showed the least horizontal movement and the brass dowel system produced the least occlusogingival reseating discrepancy.
authors.affiliation: Department of Restorative Dentistry, University of Washington, Seattle, USA.
authors.forename: J G
authors.initials: JG
authors.lastname: Serrano
authors.forename: X
authors.initials: X
authors.lastname: Lepe
authors.forename: J D
authors.initials: JD
authors.lastname: Townsend
authors.forename: G H
authors.initials: GH
authors.lastname: Johnson
authors.forename: S
authors.initials: S
authors.lastname: Thielke
mesh_terms: D000704:Analysis of Variance; D003300:Copper; D003722:Dental Alloys; D003735:Dental Casting Technique / Q000295:instrumentation / Q000592:standards* / Q000706:statistics & numerical data; D003760:Dental Impression Materials; D003761:Dental Impression Technique / Q000295:instrumentation / Q000592:standards / Q000706:statistics & numerical data; D003772:Dental Pins; D006801:Humans; D007576:Jaw, Edentulous, Partially / Q000534:rehabilitation; D008334:Mandible; D003765:Models, Dental / Q000592:standards* / Q000706:statistics & numerical data; D015203:Reproducibility of Results; D013193:Stainless Steel; D015032:Zinc
chemical_list: D003722:Dental Alloys; D003760:Dental Impression Materials; D013193:Stainless Steel; C048399:brass; D003300:Copper; D015032:Zinc