Effects of Viscosity of Silicone Impression Materials on the Accuracy of Working Model for Implants

Objectives: The purpose of this study was to compare the dimensional accuracy of three different viscosities of the various silicone impression materials and compare the impression techniques between 1-step and 2-step.
Methods: Six different brands (Imprint II, 3M ESPE; Aquasil, Dentsply; Honigum, DMG; Examixfine, GC; Vonflex S, Vonflex S-new, Vericom) of impression materials with 3 different viscosity (light-body, medium-body, heavy-body) were tested. A machined aluminum arch was fabricated to serve as a master model, simulating an edentulous dental arch. Five parallel holes were drilled perpendicular to the aluminum block, and five internal-octagon implants were positioned parallel to each other. For each group, ten impressions were taken using 1-step (light-body/putty, medium-body, heavy-body) and 2-step (light-body/putty) technique. Five definitive casts were obtained after 1 hr. The center-to-center distances between the solid abutments of the five implants in each definitive cast and a solid aluminum master model were measured in the horizontal plane using a computer-aided microscope. The dimensional accuracy was evaluated using differences between distances in aluminum master model and distances in definitive cast. The data were analyzed using t-test and Newman-Keuls multiple comparisons test (p=0.05).
Results: Distances between each abutment in definitive cast from the light-body/putty systems were longer than those from the aluminum master model itself regardless of impression techniques (1-step or 2-step). Light-body/putty systems (1-step or 2-step) showed less dimensional accuracy than the medium-body 1-step or heavy-body 1-step. Distances between each abutment in definitive cast from the medium-body or heavy-body impression 1-step techniques were shorter than those from the aluminum master model itself. Light-body/putty 1-step technique showed less dimensional accuracy than the light-body/putty 2-step technique (p<0.05) , except for Dentsply.
Conclusions: : It can be suggested that medium body or mono-phase silicone impression materials rather than light-body/putty combination may recommend the impression taking for implant-retained prosthesis.