Comparison of Three-Dimensional Accuracy of Digital and Conventional Implant Impressions: Effect of Interimplant Distance in an Edentulous Arch

Purpose: This study compared the three-dimensional (3D) accuracy of conventional impressions with digital impression systems (intraoral scanners and dental laboratory scanners) for two different interimplant distances in maxillary edentulous arches. Materials and Methods: Six impression systems comprising one conventional impression material(Impregum), two intraoral scanners (TRIOS and True Definition), and three dental laboratory scanners (Ceramill Map400, inEos X5, and D900) were evaluated on two completely edentulous maxillary arch master models (A and B) with six and eight implants, respectively. Centroid positions at the implant platform level were derived using either physical or virtual probe hits with a coordinate measuring machine. Comparison of centroid positions between master and test models (n = 5) defined linear distortions (d_x, d_y, d_z), global linear distortions (d_R), and 3D reference distance distortions between implants (ΔR). The two-dimensional (2D) angles between the central axis of each implant to the x- or y-axes were compared to derive absolute angular distortions (Absdθ_x, Absdθ_y). Results: Model A mean d_R ranged from 8.7 ± 8.3 μm to 731.7 ± 62.3 μm. Model B mean d_R ranged from 16.3 ± 9 μm to 620.2 ± 63.2 μm. Model A mean Absdθ_x ranged from 0.021 ± 0.205 degrees to -2.349 ± 0.166 degrees, and mean Absdθ_y ranged from -0.002 ± 0.160 degrees to -0.932 ± 0.290 degrees. Model B mean Absdθ_x ranged from -0.007 ± 0.076 degrees to -0.688 ± 0.574 degrees, and mean Absdθ_y ranged from -0.018 ± 0.048 degrees to -1.052 ± 0.297 degrees. One-way analysis of variance (ANOVA) by Impression system revealed significant differences among test groups for d_R and ΔR in both models, with True Definition exhibiting the poorest accuracy. Independent samples t tests for d_R, between homologous implant location pairs in Model A versus B, revealed the presence of two to four significant pairings (out of seven possible) for the intraoral scanner systems, in which instances d_R was larger in Model A by 110 to 150 μm. Conclusion: Reducing interimplant distance may decrease global linear distortions for intraoral scanner systems, but had no effect on Impregum and the dental laboratory scanner systems. Impregum consistently exhibited the best or second-best accuracy at all implant locations, while True Definition exhibited the poorest accuracy for all linear distortions in both models A and B. Impression systems could not be consistently ranked for absolute angular distortions. Keywords: 3D accuracy, CMM, dental laboratory scanner, digital impression, implant, intraoral scanner