Beschreibung
The purpose of the present study was to investigate the transfer accuracies of conventional and digital implant impression taking with different impression trays and intraoral scanners in vitro. The aim was to determine whether additively manufactured impression trays and prefabricated foil impression trays represent an alternative to conventionally manufactured individual impression trays in terms of the impression accuracy achieved. To date, there are no known studies that evaluate the cantilever accuracy for full-arch implant impressions with a reference system and compare the above-mentioned impression methods with each other.
To investigate the impression accuracy, individual impression trays were additively manufactured on a master model (reference model) with four implants and a reference cuboid using two different 3D printers (SHERAprint, SHERA Werkstofftechnologie, Lemförde, Germany; Primeprint, Sirona, Bensheim, Germany), and an individual impression tray was conventionally manufactured in the dental laboratory. Ten pick-up impressions (Impregum, 3M Espe, Seefeld, Germany) were taken on each of these impression trays and a prefabricated foil impression tray (Miratray Implant, Hager und Werken, Duisburg, Germany) and conventional plaster models were fabricated on the described master model. In addition, ten digital impressions of the reference model were made using three different intraoral scanners (Trios 4, 3Shape, Copenhagen, Denmark; i700, Medit Seoul, South Korea; Primescan, Sirona, Bensheim, Germany). After tactile measurement of the conventional models in a coordinate measuring machine, all models were evaluated and compared with a previously generated reference data set of the original model using 3D analysis software (GOM Inspect 2019, Braunschweig, Germany). A defined coordinate system was applied to each model in the area of the reference cube, allowing the coordinates of the implant centers and their linear deviation from the reference points to be determined.
Of all the methods investigated, the two 3D printed trays showed the significantly highest impression accuracy. However, no significant difference in transfer accuracy was found between all other methods, both intra-oral scanners and conventional impression trays, with the conventional impression tending to achieve the higher transfer accuracy.
The conventional impression in general also showed a constant deviation over the entire jaw, whereas a higher deviation of the implant positions with increasing scan path length was observed for the digital implant impression.
In summary, the in vitro results suggest that additively manufactured custom impression trays are an alternative to conventionally manufactured custom impression trays for implant impression taking. Conventional implant impression taking with customized trays provides higher accuracy for full-arch impressions than digital impression taking. Further studies would be desirable for an absolute statement on clinical transferability.
