[Quantitative study of intraoral scanners' accuracy]

Objective: To establish a standard method to evaluate the scanning accuracy of intraoral scanner (IOS) and to investigate six IOS's scanning accuracy and the relationship between different scan span. Methods: Five simplified six abutments full arch model were fabricated by high accuracy (5 μm) milling machine with 7075 aluminum alloy. The machining accuracy, which was verified by a coordinate measuring machine with higher accuracy (0.7 μm), was considered as the reference accuracy. The model with the highest machining accuracy was considered as the test model in IOS's scanning accuracy test, and computer-aided design (CAD) data of the model was used as the reference data. Six IOS scanned the test model 10 times with the same scanning path, obtained 60 test data. CAD data and test data were input into Geomagic Studio 2014. The preparation part above the margin of the abutments of the data was isolated and divided into 4 segments of interest: single crown, three-unit bridge, five-unit bridge, and full arch. The test data were then best-fit aligned to CAD data or each other followed by deviation analysis. Scanning trueness and precision were then calculated. Results: The mid-value of scanning trueness and precision of six IOS in single crown, three-unit bridge, five-unit bridge and full arch were 13.3-29.6 μm and 7.6-20.7 μm, 15.4-30.9 μm and 8.7-26.5 μm, 17.0-66.1 μm and 11.3-44.2 μm, 24.0-107.9 μm and 24.6-150.1 μm respectively. Conclusions: Long-span scanning can affect the accuracy of IOS to a varying extent.