[Influence of scanning aid material and post space parameters on the trueness of intraoral scanners for post space: an in vitro study].

Objective: To investigate the effects of different post space parameters and scanning aid material on the trueness of digital impressions of post spaces obtained by two intraoral scanners, thereby providing a reference for clinically determining the conditions under which post spaces are suitable for digital impression technology. Methods: This study varied three variables of post space models of residual crowns: opening diameter, post space depth and adjacent tooth status,with specific settings: opening diameter were set at two levels (2.0 and 2.5 mm);post space depth was set at three levels (8.0, 10.0, and 12.0 mm); and adjacent tooth status were set at three levels [bilateral adjacent teeth present (A), unilateral adjacent tooth present (B), and bilateral adjacent teeth absent (C)]. A total of 18 model groups were prepared. Eighteen samples were printed using a three-dimensional printing instrument. Combined with scanning aid material, direct in vitro scanning of these post space models was performed using intraoral scanners (IOS) A (Trios 5) and B (Primescan connect), with 10 replicates per group (n=10). The scanned data were sequentially imported into reverse engineering software. The original design data of the models served as true values, and best-fit comparisons were performed. By calculating the average root mean square error (RMSE) values, the trueness of digital impressions of post spaces with different morphologies obtained by the two scanners was evaluated, both with and without the use of scanning aid material. Results: Under the experimental conditions set in this study, for IOS A, only the sample groups with opening diameter-post space depth-adjacent tooth status combinations of (2.0 8.0 ABC, 2.5 8.0 ABC, 2.5-10.0-ABC) could be identified, with RMSE results ranging from 46.5 to 365.0 μm. After adding scanning aid materials,RMSE results ranging from 46.0 to 185.0 μm, the trueness of the sample groups (2.0-8.0-A, 2.5-10.0-A) was significantly improved by more than 100 μm, and an additional sample group (2.5-12.0-C) could be identified. For IOS B, the identifiable sample groups included all 18 sample groups, with RMSE results ranging from 38.8 to 106.0 μm. After the addition of scanning aid materials, RMSE results ranging from 37.6 to 110.2 μm, the identifiable sample groups remained unchanged. Post space opening diameter, post space depth, and adjacent tooth status all had significant effects on the trueness of post space digital impressions for both IOS A and IOS B (P<0.05). Scanning aid materials had a significant effect on IOS A (P<0.05) but no significant effect on IOS B (P>0.05). Conclusions: IOS B exhibited superior post space scanning performance compared to IOS A, and its trueness for clinically common post spaces could meet clinical requirements. IOS A has certain requirements for post space opening diameter, post space depth, and adjacent tooth status. For narrow and long post spaces, scanning aid materials can be used to improve the scanning trueness.