[Effect of digital intraoral full-arch scan strategies on scan time and accuracy on conditions of intraoral head-simulator].

To comparatively evaluate the accuracy and the scan time of three full-arch scan strategies on the head-simulator, to explore a full-arch scan strategy with better clinical operability and high accuracy. A cross-controlled study design was used. A model with melamine-formaldehyde resin teeth and silica gel gingiva of an upper dental arch which can be fixed on a head simulator was scanned with an optical scanner (ATOS Core) in order to obtain the standard tessellation language (STL) dataset as reference. Intraoral scans were performed on the model fixed on the head simulator with four intraoral scanners (IOS) [A (TRIOS 3), B (CS 3600), C (CEREC Omnicam), D (iTero)]. The STL datasets were obtained from each of the four different IOS systems by using three scan strategies (scan strategies 1, 2 and 3 were composed of 10, 5 and 7 paths respectively) all by one attending doctor with 3 years of intraoral scanning experience. For each scanner and each scan strategy, nine scans were acquired. And the scan time was recorded for each scan. Following the scan strategy, the scan path was completed to obtain a full-arch digital model, and the scan time was recorded as full-arch scan time. Complementary scans were performed to fill the missing image, and this scan time was recorded as complementary scan time. The total scan time was obtained by adding full-arch scan time and complementary scan time. Through the Geomagic Wrap software, the three-dimensional (3D) models were overlaid by best fit alignment function and compared to obtain the root mean square values of the discrepancies by 3D compare function. The intraoral scanning datasets were compared with the reference for trueness. The nine intraoral scanning datasets were cross compared with same scan strategy and same intraoral scanner for precision. There were no significant differences among the three scan strategies for trueness (>0.05), while the differences among the three scan strategies for precision were affected by difference IOSs (<0.05), and only scan strategy 3 showed the highest precision with all the four IOS. The full-arch scan time of scan strategies 1, 2 and 3 were (130±24), (72±17) and (90±19) s respectively (<0.05). For complementary scan time, scan strategy 2 [(50±24) s] took longer time than scan strategy 1 [(26±18) s] and scan strategy [(25±21) s] (<0.05), while no significant differences between the latter two (>0.05). For total scan time, scan strategy 1 [(156±31) s] took longer time than scan strategy 2 [(122±30) s ] and scan strategy 3 [(115±29) s ] (<0.05), while no significant differences between the latter two (>0.05). Full-arch scanning on the head-simulator with scan strategy 3 which can obtain scanning datasets with high accuracy, was more convenient to operate and took shorter scan time, and is generally suitable for intraoral scanners commonly used in clinic.