Comparing the accuracy of intraoral scanners, using advanced micro computed tomography

Intraoral scanners have been gaining importance in dental offices. The technology has become a valuable and economically reasonable alternative to conventional silicone impressions and the conventional plaster casts because of the reduced treatment time and the sufficient precision achieved. The required precision of the dental prostheses depends on the clinical needs. For the production of working models, the tolerable inaccuracy is relatively large. Especially for crowns, bridges and larger dental prostheses, which include several teeth over the dental arch, however, extra work is often performed, that presumably caused by the limited accuracy of intraoral scanners. Therefore, the paper deals with the detailed evaluation of selected, commercially available intraoral scanner systems. For this purpose, we have designed and realized a model of a full arch upper jaw on the basis of clinically relevant imaging data. As well-defined references, we have incorporated cylinders with a diameter of 4 mm. This standard to be used as reference, was quantitatively characterized by four independent measurements using the advanced CT-system phoenix nanotom® m (GE Sensing & Inspection Technologies GmbH, Wunstorf, Germany) with a pixel size of 35 μm. The standard was also scanned using five commercially available intraoral scanners. In order to compare the accuracy of the ten measurements per scanner, the data were matched to the standard. Their displacements were made visible with GOM Inspect (GOM GmbH Braunschweig, Germany). Applying the same approach, we have analyzed the accuracy of two three-dimensionally printed dental models by the stereolithography printers Form 2, Formlabs Inc., Somerville MA, USA). The results demonstrate the currently possible level of precision by the selected intraoral scanners. They differ, however, not only in scanning time necessary and the ease of handling, but also in reachable accuracy. The precision ranged from (35 ± 5) μm (TRIOS® 3) to (97 ± 22) μm (EmeraldTM). The largest deviations to the standard were found in the transversal plane (412 ± 247) μm (Medit i500). The combination of advanced conventional microCT and adequate software for quantitative analysis permits a detailed evaluation of the performance of the currently available intraoral scanners.