Accuracy of impression techniques for an implant-supported prosthesis

Objectives: This in vitro study compared the dimensional accuracy of a stone index (control group) and of 2 impression techniques (squared impression copings and squared modified impression copings) for implant-supported prostheses. Materials and Methods: A mandibular brass cast with 4 stainless steel implant abutment analogues (master cast) and a passive implant framework were fabricated. Polyvinilsiloxane impression material (Express putty-light body-3M ESPE) was used for all impressions with a metal stock tray. Three groups (n=5): Index (I); Squared (S) and Squared Modified (SM) were tested. The measurement method employed was just one titanium screw tightened to the framework. The marginal gap measurements between analog and abutment were recorded with a Leica optical microscope at x100 magnification. The mean value of master cast was 31.63µm. Group's measurements (60 gap values) were analyzed using software (Leica QWin - Leica Imaging Systems Ltd) that received the images of a video camera coupled to microscope. The results were statistically analyzed (ANOVA, Holm-Sidak method, p<0.05). Results: The mean values of abutment/framework interface gaps were: I=45.25µm; S=96.14µm; SM=51.20µm. No significant difference was detected among I and SM techniques. Conclusion: The more accurate impression technique was SM. The techniques I or SM are preferred methods for making implant-supported fixed restorations with exceptional dimensional accuracy.