An evaluation of impression techniques for multiple internal connection implant prostheses

Abstract

Movement of impression copings inside the impression material using an open-tray impression technique during clinical and laboratory phases may cause inaccuracy in transferring the 3-dimensional spatial orientation of implants intraorally to the definitive cast. Consequently the restoration may require corrective procedures. This in vitro study evaluated the accuracy of 3 different impression techniques using polyether impression material to obtain a precise definitive cast for a multi-unit implant restoration with multiple internal connection implants. A reference acrylic resin model with 4 internal connection implants (3i Implant Innovations) was fabricated. Forty-five medium-consistency polyether impressions (Impregum Penta) of this model were made with square impression copings using an open-tray technique. Three groups of 15 specimens each were made with different impression techniques: in the first group, nonmodified square impression copings were used (NM group); in the second group, square impression copings were used and joined together with autopolymerizing acrylic resin before the impression procedure (R [resin] group); and in the third group, square impression copings previously airborne-particle abraded and coated with the manufacturer-recommended impression adhesive were used (M [modified] group). Matching implant replicas were screwed into the square impression copings in the impressions. Impressions were poured with ADA type IV stone (New Fujirock). A single calibrated examiner blinded to the nature of the impression technique used examined all definitive casts to evaluate the positional accuracy (μm) of the implant replica heads using a profile projector (at original magnification ×10). These measurements were compared to the measurements calculated on the reference resin model which served as control. Data were analyzed with a 1-way analysis of variance at α=.05, followed by the Student Newman-Keuls test (α=.05). The data obtained with the profile projector revealed significant differences within the 3 impression techniques (P