Effect of using auxiliary geometric part on digital impression precision in full ARCH restorations: An in vitro study

The use of digital impression is increasing day by day in the production of implant supported prostheses. However, conflicting results were reported when there are wide toothless areas between implants. The aim of this study is to evaluate the passive fit of implant supported multi-unit screwed superstructures fabricated via conventional, digital impressions and digital impressions with the aid of auxiliary geometric part. In this in-vitro study, an epoxy resin master cast simulating an edentulous maxilla with four implants was used as a reference model. The abutments of the screwed superstructure were torqued onto the implants. Impressions were taken from this reference model with four different methods: Scanning with a laboratory scanner over a direct reference model, splinted open tray technique, digital impression with intraoral scanner, digital impression with intraoral scanner using an acrylic auxiliary geometric part which will create an uninterrupted reference point between the scan bodies. Using the data obtained, a single piece screwed metal superstructure was produced by the SLM method. Sheffield test was applied to evaluate passive fit of the restorations. Misfits between each abutment and superstructure that occurred during the test was evaluated with a stereomicroscope at x45 magnification. One-way ANOVA was used to evaluate the effect of the measurement method on the vertical marginal gap (VMA), and Scheffe posthoc test was used for pairwise comparisons. As a result of the study, it was found that there was a significant difference between the measurement methods. The average VMA values of the superstructures produced by digital impression technique are significantly higher than the other groups. It was determined that the use of auxiliary geometric part improved the digital measurement accuracy.