title: Influence of tray rigidity and impression technique on accuracy of polyvinyl siloxane impressions.
abstract: OBJECTIVE
  The aim of this study was to determine how tray rigidity and impression technique affect the accuracy of polyvinyl siloxane impressions.
  
  
  METHODS
  Disposable plastic trays and metallic Rim-Lock trays were used in combination with a heavy/light body technique or with two different putty-wash techniques. For each technique-tray combination, 10 impressions were made of a master cast with two steel abutments representing the mandibular right first premolar and second molar, between which a steel rod was placed at the ridge level. Each steel abutment had five marks, while the steel rod in between the two abutments had only one mark, which served as a reference point. With a universal measuring microscope, the x-, y-, and z-coordinates were recorded for each mark on the master cast and impressions. The distances between the different marks and the reference point on the impressions were calculated and compared with those of the master cast.
  
  
  RESULTS
  All techniques used with the plastic trays had distances that were significantly different from the master cast (P < .05), while for the metal trays, it was only the heavy/light body technique that resulted in distances that were significantly different from the master cast (P < .05).
  
  
  CONCLUSIONS
  Plastic trays produced less accurate impressions than metal trays. When metal trays were used, putty-based impressions were dimensionally better than heavy/light body impressions.
authors.affiliation: Department of Prosthodontics, University of Florida, Gainesville, FL, USA.
authors.forename: Alex
authors.initials: A
authors.lastname: Hoyos
authors.forename: Karl-Johan
authors.initials: KJ
authors.lastname: Soderholm
mesh_terms: D001641:Bicuspid; D000044:Dental Abutments; D003722:Dental Alloys / Q000737:chemistry; D003760:Dental Impression Materials / Q000737:chemistry*; D003761:Dental Impression Technique / Q000295:instrumentation* / Q000592:standards; D004209:Disposable Equipment; D055119:Elastic Modulus; D004867:Equipment Design; D006801:Humans; D006813:Humidity; D008422:Materials Testing; D008853:Microscopy; D008963:Molar; D010969:Plastics / Q000737:chemistry; D011145:Polyvinyls / Q000737:chemistry*; D012833:Siloxanes / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors; D014783:Viscosity
chemical_list: D003722:Dental Alloys; D003760:Dental Impression Materials; C502512:Exaflex type O; D010969:Plastics; D011145:Polyvinyls; D012833:Siloxanes; C480691:aquasil; C034183:vinyl polysiloxane