title: The effect of impression volume and double-arch trays on the registration of maximum intercuspation.
abstract: BACKGROUND
  The type of double-arch trays used may affect occlusion.
  
  
  OBJECTIVE
  The purpose of this study was to determine what effect, if any, double-arch tray design and impression material volume had on the registration of maximum intercuspation (MI).
  
  
  METHODS
  Quadrant impressions were made on articulated fracture-resistant dental casts mounted in maximum intercuspation occlusion. Three types of sideless double-arch impression trays were used: First Bite with nylon webbing, Sultan's 3-Way with double crosshatch webbing, and Premium's 3-in-1 Tray with single crosshatch webbing. Vinyl polysiloxane impression material (Aquasil Ultra Rigid Fast Set) was distributed at 2 different volumes (5.4 ml and 8.3 ml), and 60 impressions were made (n=10). A weight of 1.2 kg was placed on the upper arm of an Artex articulator, ensuring complete closure. The impressions were allowed to polymerize for 5 minutes. After polymerization, specimens were placed on a light box, and a camera set at a fixed distance was used to capture the light transmission that was projected through the impression material. The camera transferred the information to an image analysis program (ImageJ). This system allowed the different amounts of light projected through the impression to be translated into a gray scale value (GSV), which was assigned a thickness value, in millimeters, of a specified occlusal contact area. To assess reliability of the experimental design, 10 control impressions were made by directly applying impression material onto the typodont. These were analyzed in the same manner as the impressions made with trays. A 2-way ANOVA comparing volume by tray type was used (alpha=.05). This was followed by a Tukey HSD test.
  
  
  RESULTS
  There was no main effect for volume of impression material (P=.71). Tray type was significantly different (P<.001). Impressions made with Sultan trays were significantly less accurate than impressions made with First Bite or Premium impression trays. The Premium tray type had the highest mean (SD) GSV, 179.8 (8.1), significantly higher than First Bite (164.7 (19.8); P<.001) or Sultan (82.8 (7.4); P<.001) trays.
  
  
  CONCLUSIONS
  This in vitro study demonstrated that certain trays hinder closure into MI, which may negatively affect the accuracy of record making.
authors: Harvard School of Dental Medicine, Boston, MA 02115, USA. sara_hahn@hsdm.harvard.edu
authors: Sara M
authors: SM
authors: Hahn
authors: Philip L
authors: PL
authors: Millstein
authors: Taru H
authors: TH
authors: Kinnunen
authors: Robert F
authors: RF
authors: Wright
mesh_terms: D003725:Dental Articulators; D003760:Dental Impression Materials; D003761:Dental Impression Technique / Q000295:instrumentation*; D003768:Dental Occlusion, Centric; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007574:Jaw Relation Record; D003765:Models, Dental; D011145:Polyvinyls; D012833:Siloxanes; D014172:Transillumination
chemical_list: D003760:Dental Impression Materials; D011145:Polyvinyls; D012833:Siloxanes; C034183:vinyl polysiloxane