Effect of Implant Divergence on the Accuracy of Definitive Casts Created from Traditional and Digital Implant-Level Impressions: An In Vitro Comparative Study

Purpose: The purpose of this research was to compare the accuracy of definitive casts created with digital and conventional methods for implants with internal-octagon connections placed parallel or at different angles (15, 30, or 45 degrees). Materials and Methods: Four customized epoxy resin master casts were fabricated with two-implant analogs placed in the posterior mandible with different degrees of divergence. For the conventional (control) group, 10 traditional impressions were taken on each master cast with custom trays, open-tray impression copings, and polyvinyl siloxane; definitive stone casts were poured with type IV dental stone. For the digital group, 10 digital impressions were taken on each master cast with two-piece scannable impression copings and an intraoral digital scanner; definitive milled polyurethane casts were fabricated by the manufacturer. All four master casts and 80 control and test casts were scanned and digitized, and the data sets were compared. Any deviations in measurements between the definitive and corresponding master casts were analyzed statistically. Results: The amount of divergence between implants did not affect the accuracy of the stone casts created conventionally; however, it significantly affected the accuracy of the milled casts created digitally. A decreasing linear trend in deviations for both distance and angle measurements suggested that the digital technique was more accurate when the implants diverged more. At 0 and 15 degrees of divergence, the digital method resulted in highly significantly less accurate definitive casts. At 30 and 45 degrees of divergence, however, the milled casts showed either no difference or marginal differences with casts created conventionally. Conclusion: The digital pathway produced less accurate definitive casts than the conventional pathway with the tested two-implant scenarios. To ensure passive fit of definitive prostheses, verification devices and casts may be used when materials are produced digitally.