Accuracy of multi-unit implant impression: traditional techniques versus a digital procedure

The objective of this study was to evaluate the accuracy of different impression techniques on multiple implants. A master cast simulating a jaw with four implants was used. Eight impression techniques were tested: open tray-polyether#1, open tray plus splint of impression copings with acrylic resin-polyether#1, closed tray-polyether#1, open tray-polyether#2, open tray-splint-polyether#2, closed tray-polyether#2, open tray-impression plaster, and digital impression (DI). Five impressions of the master cast were taken with each traditional impression (TI) technique, pouring 35 sample casts. Three different clinicians took 5 DI each (n = 15). A three-dimensional coordinate measurement machine (CMM) was used to measure implant angulation and inter-implant distances on TI casts. TI data and DI Standard Tessellation Language datasets were compared with the master cast. The best and the worst impressions made with TI and DI were selected to fabricate four milled titanium frameworks. Passive fit was evaluated through Sheffield test, screwing each framework on the master cast. Gaps between framework-implant analogs were measured through a stereomicroscope (x40 magnification). Statistically significant differences in accuracy were found comparing the different impression techniques by CMM (p < 0.01). DI performed the best, while TI techniques revealed a greater variability in the results. Sheffield test revealed a mean gap of 0.022 +/- 0.023 mm (the best TI), 0.063 +/- 0.059 mm (the worst TI), 0.015 +/- 0.011 mm (the best DI), and 0.019 +/- 0.015 mm (the worst DI). Within the limits of this in vitro study, the digital impression showed better accuracy compared to conventional impressioning. The digital impression might offer a viable alternative to traditional impressions for fabrication of full-arch implant-supported prostheses with satisfactory passive fit.