title: Influence of polyurethane resin dies on the fit and adaptation of full veneer crowns.
abstract: BACKGROUND
  Polyurethane resin is a possible alternative to type IV dental stone for fabrication of indirect restorations however its dimensional accuracy is questionable.
  
  
  OBJECTIVE
  The aim was to investigate the dimensional accuracy of silica filled polyurethane resin die material by evaluating the marginal fit and adaptation of indirect gold castings.
  
  
  METHODS
  Experimental, in vitro study.
  
  
  METHODS
  Totally 40 copper plated replicas of a nickel chrome master die analogous to a veneer gold crown preparation were made and impressions recorded using polyvinylsiloxane material. Twenty impressions were poured in type IV dental stone (control group (Vel-mix, Kerr, UK) and the remaining (n = 20) in silica filled polyurethane die material (test group) (Alpha Die MF, CA, USA). Gold castings were fabricated for each die using standardized techniques. The castings were seated on their respective copper plated dies, embedded in resin and sectioned. The specimens were analyzed by measuring marginal opening and the area beneath the casting at a ×63 magnification and using image analysis software.
  
  
  METHODS
  Data were analyzed using a Student's t-test.
  
  
  RESULTS
  No significant difference was observed between the experimental groups (P > 0.05). The mean marginal opening for type IV, dental stone and polyurethane resin, was 57 ± 22.6 μm and 63.47 ± 27.1 μm, respectively. Stone displayed a smaller area beneath the casting (31581 ± 16297 μm 2 ) as compared to polyurethane resin (35003 ± 23039 μm 2 ).
  
  
  CONCLUSIONS
  The fit and adaptation of indirect gold castings made on polyurethane and type IV dental stone dies were comparable.
authors.forename: Graeme R R
authors.initials: GR
authors.lastname: Lillywhite
authors.affiliation: Department of Prosthetic Dental Science, College of Dentistry, King Saud University, Riyadh 11545, Kingdom of Saudi Arabia.
authors.forename: Fahim
authors.initials: F
authors.lastname: Vohra
mesh_terms: D003300:Copper / Q000737:chemistry; D003442:Crowns; D003735:Dental Casting Technique; D003801:Dental Veneers; D006046:Gold / Q000737:chemistry; D006801:Humans; D066298:In Vitro Techniques; D011140:Polyurethanes / Q000737:chemistry*; D011145:Polyvinyls / Q000737:chemistry; D012833:Siloxanes / Q000737:chemistry
chemical_list: D011140:Polyurethanes; D011145:Polyvinyls; D012833:Siloxanes; C034183:vinyl polysiloxane; D006046:Gold; D003300:Copper