Effect of span length on the trueness of an intraoral scanner. (An in-vitro study)

Abstract
Statement of the problem:
Digital scanning has been widely used nowadays, however its accuracy in relation to the bridge span length needs further investigations.
Objective:
The aim of this study was to determine the effect of span length on the trueness of an intra-oral scanner.
Materials and methods:
On a typodont (Nissin Dental Model, Japan) preparations for two bridge span lengths were made. One resembling missing upper second premolar representing short straight span length (SS) while the second resembling missing upper first and second premolars representing long curved span (LS). Then typodont was scanned by a laboratory scanner (InEos X5 scanner) (Sirona Dental System, Bensheim, Germany) to act as a reference model scan to compare measurements for trueness. Then for each group five scans were taken for the typodont by Medit intraoral scanner (iScan version 1.2.0.1; Medit, Seoul, Korea) to be compared with the reference scan. Then data set from the scans were transferred to STL format and then exported to exocad (exocad version 2.3 Matera exocad GmbH,Darmstadt, Germany) software to get the measurements to determine the trueness.
Results:
Results of this study showed that in the comparison between short and long span bridges, the long span bridge scans showed statistically significant higher root mean square (RMS) mean value (0.23±0.10 mm), lower trueness than short span bridge scans (0.06±0.04 mm).
Conclusions:
Long span fixed bridge had an adverse effect on the scanning accuracy. Trueness of intraoral scanner may be affected by the complexity and length of the scanning area.