title: The effect of sulcular width on the linear accuracy of impression materials in the presence of an undercut.
abstract: OBJECTIVE
  This study examined the effect of gingival sulcular width, in the presence of an undercut, on the accuracy of dies poured from impressions made with different impression materials.
  
  
  METHODS
  Three polyvinyl siloxanes (Examix, Elite, and Express), one polyether (Permadyne), and one polysulfide (Permlastic) were used to make impressions of six metal dies. The dies were machined to simulate teeth with a chamfer preparation, root convergence, and sulci of varying widths (0.10 to 0.40 mm). The impressions were poured with type IV stone, and the resulting dies were measured under a traveling microscope at the level of the finish line. The distortion of each die was calculated.
  
  
  RESULTS
  The distortion ranged from 0.01% to 0.89%. All materials showed similar behavior: At the narrowest sulcular width (0.10 mm), the distortion was considerably larger (0.43% to 0.89%) than at the wider sulci (up to 0.20% in most cases). Examix (polyvinyl siloxane), Permlastic (polysulfide), and Permadyne (polyether) gave the most accurate dies for sulci 0.15 mm and wider. Express (polyvinyl siloxane) showed greater deformation than other materials in most sulcular widths under the conditions of this study.
  
  
  CONCLUSIONS
  Accurate impressions can be expected in sulci > or = 0.15 mm in width at the level of the finish line coronal to an undercut. Impressions with 0.10-mm sulci widths are not predictable. The physical properties of the impression materials used cannot be anticipated based on their chemical group.
authors.affiliation: Department of Oral Rehabilitation, The Maurice and Gabriela Goldshleger School of Dental Medicine, Tel Aviv University, Israel.
authors.forename: Haim
authors.initials: H
authors.lastname: Baharav
authors.forename: Irit
authors.initials: I
authors.lastname: Kupershmidt
authors.forename: Ben-Zion
authors.initials: BZ
authors.lastname: Laufer
authors.forename: Harold S
authors.initials: HS
authors.lastname: Cardash
mesh_terms: D000704:Analysis of Variance; D003735:Dental Casting Technique; D003760:Dental Impression Materials; D005881:Gingiva / Q000033:anatomy & histology*; D006801:Humans; D008422:Materials Testing; D003765:Models, Dental; D011145:Polyvinyls; D015203:Reproducibility of Results; D012833:Siloxanes; D018709:Statistics, Nonparametric; D013440:Sulfides; D019231:Tooth Preparation, Prosthodontic
chemical_list: D003760:Dental Impression Materials; C495447:Permadyne; D011145:Polyvinyls; D012833:Siloxanes; D013440:Sulfides; C034183:vinyl polysiloxane; C032915:polysulfide