A 3-dimensional accuracy assessment of digital impression in a single implant-supported prosthesis

Objectives: To establish a metrology-based accuracy assessment method for digital impressions of a single implant-supported prosthesis
Methods:
A simulation model using human extracted teeth containing an implant analog was prepared as a master model. Three reference spheres
were attached to the model. Duplicated models (DMs) were made using conventional impression with polyvinyl siloxane. The master model
was digitised by an intraoral scanner (Dental Wings, DWIO), a laboratory scanner (Dental Wings, 7-series, DW-7) and a coordinate measuring machine (Renishaw, Incise, CMM). The DMs were digitised by CMM only. The data were analysed by 3-D software.
Results:
Based on reference spheres - The accuracy, determined by the mean deviation of measured diameter to the actual diameter of spheres (N=3), was 0.048mm for CMM, 0.142 mm for DW-7 and 0.072 mm for DWIO. The sphericity, determined by the standard deviations (SDs) of the best fit of the spheres, were 0.004, 0.012, and 0.032 mm for CMM, DW-7 and DWIO respectively.
Based on the master model - The reproducibility, determined by the SDs (N=6), was 0.00 mm for CMM, 0.02 mm for DW-7, 0.06 mm for DWIO and 0.01 mm for DM
Based on the reference device-The accuracy was determined by the mean 3-D linear deviations of the selected regions from CMM (N=6). For DWIO, the deviations were 0.19 mm over the teeth and 0.60 mm over the scan body; whereas for the DM, were 0.07 mm and 0.27 mm respectively.
Conclusions: 1.The sphericity and accuracy of the sphere digitised by CMM was the best among three digitising devices and the reproducibility of the model digitisation was the best when using CMM. Therefore, CMM can be used as a reference device for comparison with digital impressions.
2. The conventional impression had better accuracy than the intraoral scanner in a single implant-supported prosthesis when using an appropriate measurement protocol.