Effect of prefabricated auxiliary devices in different optical properties and shapes on the accuracy of intraoral scanning of the edentulous arch with multiple implants: An in-vitro study.

Objectives: This study aimed to evaluate the impact of prefabricated auxiliary devices (PADs) in different optical properties and shapes on the accuracy of digital implant impressions.

Methods: An edentulous maxillary all-on-4 master model was fabricated. PADs were 3D-printed in different resin materials (Grey, Translucent, White, Yellow) and shapes (Cuboid, Cylinder, Sphere) using a 3D printer (AccuFab-C1s, 3DShining, Hangzhou, China). The master model was digitalized using a dental laboratory scanner (D2000, 3Shape, Copenhagen, Denmark) 4 times as the reference models. Test models were obtained without (control group) or with PADs by an intraoral scanner (Aoralscan 3, Shining3D, Hangzhou, China) for ten repetitions of each group using the scanning pattern recommended by the manufacturer. The related files were imported into inspection software to assess Root Mean Square (RMS), linear and angular accuracy. Aligned Ranks Transformation ANOVA, Kruskal-Wallis and Mann-Whitney tests were used to evaluate the differences in these values. The level of significance was set at α=0.05.

Results: PADs in different optical properties and shapes demonstrated accuracy enhancement to different extents depending on their combinations. The PADs in combinations of white-cuboid, grey-sphere and yellow-sphere demonstrated the optimal trueness enhancement. The Aligned Ranks Transformation ANOVA indicated that the optical properties of the PADs significantly influenced the RMS, linear and angular accuracy. The main effect of optical properties indicated that translucent PADs generally generated more deviations than the others. The shapes of the PADs significantly influenced the angular accuracy. The main effect of shapes indicated that cylinder resulted in lower angular trueness on YZ plane than cuboid (p = 0.006) and sphere (p < 0.001).

Conclusion: The optical properties and shapes of the PADs significantly influenced the scanning accuracy. Translucent PADs demonstrated more deviations than the others. Lower angular trueness on the YZ plane was seen in cylinder design compared to the others.

Clinical Significance: The optical properties and shapes of prefabricated auxiliary devices should be critically considered to optimize the scanning accuracy. Prefabricated auxiliary devices in translucent optical properties and cylinder shape should be avoided.