title: Dimensional accuracy of pickup implant impression: an in vitro comparison of novel modular versus standard custom trays.
abstract: OBJECTIVE
  The purpose of this in vitro study was to compare the dimensional accuracy of the pickup impression technique using a modular individual tray (MIT) and using a standard individual tray (ST) for multiple internal-connection implants. The roles of both materials and geometric misfits were considered.
  
  
  METHODS
  First, because the MIT relies on the stiffness and elasticity of acrylic resin material, a preliminary investigation of the resin volume contraction during curing and polymerization was done. Then, two sets of specimens were tested to compare the accuracy of the MIT (test group) to that of the ST (control group). The linear and angular displacements of the transfer copings were measured and compared during three different stages of the impression procedure. Experimental measurements were performed with a computerized coordinate measuring machine.
  
  
  RESULTS
  The curing dynamic of the acrylic resin was strongly dependent on the physical properties of the acrylic material and the powder/liquid ratio. Specifically, an increase in the powder/liquid ratio accelerated resin polymerization (curing time decreases by 70%) and reduced the final volume contraction by 45%. However, the total shrinkage never exceeded the elastic limits of the material; hence, it did not affect the coping's stability. In the test group, linear errors were reduced by 55% and angular errors were reduced by 65%.
  
  
  CONCLUSIONS
  Linear and angular displacements of the transfer copings were significantly reduced with the MIT technique, which led to higher dimensional accuracy versus the ST group. The MIT approach, in combination with a thin and uniform amount of acrylic resin in the pickup impression technique, showed no significant permanent distortions in multiple misalignment internal-connection implants compared to the ST technique.
authors.affiliation: pierosimeone@hotmail.it
authors.forename: Piero
authors.initials: P
authors.lastname: Simeone
authors.forename: Pier Paolo
authors.initials: PP
authors.lastname: Valentini
authors.forename: Roberto
authors.initials: R
authors.lastname: Pizzoferrato
authors.forename: Folco
authors.initials: F
authors.lastname: Scudieri
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D003758:Dental Implantation, Endosseous / Q000295:instrumentation* / Q000379:methods; D003760:Dental Impression Materials / Q000737:chemistry*; D003761:Dental Impression Technique / Q000295:instrumentation*; D017267:Dental Prosthesis Design / Q000295:instrumentation* / Q000379:methods; D006801:Humans; D008422:Materials Testing; D003765:Models, Dental; D015203:Reproducibility of Results
chemical_list: D000180:Acrylic Resins; D003760:Dental Impression Materials