title: A clinical comparison of two vinyl polysiloxane impression materials using the one-step technique.
abstract: BACKGROUND
  Impression making remains a challenging procedure due to the potential for voids and tears, which may adversely affect the precise fabrication of indirect restorations.
  
  
  OBJECTIVE
  The purpose of this study was to compare vinyl polysiloxane (VPS) impression materials using the 1-step impression technique for single and 2-unit crowns.
  
  
  METHODS
  Twenty subjects provided informed consent, and two 1-step double-phase master impressions (1 of each material combination) were made of 25 crown preparations. A relatively new VPS material with heavy-body (HB) and light-body (LB) viscosities, which was defined as the experimental group (Imprint 3), was compared to a standard VPS with medium-body (MB) and light-body (LB) viscosities, which was defined as the control group (Aquasil Ultra). Stock trays were used to make a total of 40 master impressions. The order of impression making was randomized as related to the different groups. Impressions were rated visually by 2 evaluators (a clinician and a dental technician). The rating resulted in ordinally structured data for the outcome variables (alpha: excellent, no defects; bravo: acceptable, small defects; charlie: defects require impression to be remade; delta: unacceptable, defects at finish line). Definitive casts made of impressions rated as alpha or bravo were further rated by a dental technician, and that which was rated best was used for making the definitive crown.
  
  
  RESULTS
  Twenty-three (92%) of the experimental and 24 (96%) of the control impressions were rated as alpha or bravo by the evaluator (P=.57; McNemar's test for clustered paired proportions using GEE). All 25 dies in the definitive casts of both groups were rated as alpha or bravo by the dental technician. Fifteen dies were selected from the control group and 10 from the experimental group for the fabrication of the definitive crowns (P=.41; 1-sample binomial test for clustered data using GEE).
  
  
  CONCLUSIONS
  Within the limitations of this clinical study, there was no statistical difference in the clinical performance of the experimental and control VPS impression materials. (J Prosthet Dent 2009;102:179-186).
authors.affiliation: Graduate Prosthodontics, Department of Restorative Dentistry, School of Dentistry, University of Washington, Seattle, Wash, USA. araigrod@u.washington.edu
authors.forename: Ariel J
authors.initials: AJ
authors.lastname: Raigrodski
authors.forename: Sami
authors.initials: S
authors.lastname: Dogan
authors.forename: Lloyd A
authors.initials: LA
authors.lastname: Mancl
authors.forename: Harald
authors.initials: H
authors.lastname: Heindl
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003442:Crowns; D003760:Dental Impression Materials / Q000737:chemistry*; D003761:Dental Impression Technique; D017267:Dental Prosthesis Design / Q000295:instrumentation / Q000379:methods; D006801:Humans; D008875:Middle Aged; D003765:Models, Dental / Q000592:standards*; D015588:Observer Variation; D011145:Polyvinyls / Q000737:chemistry*; D015203:Reproducibility of Results; D012833:Siloxanes / Q000737:chemistry*; D018709:Statistics, Nonparametric
chemical_list: D003760:Dental Impression Materials; D011145:Polyvinyls; D012833:Siloxanes; C034183:vinyl polysiloxane