# Computerized Optical Impression Making of Fully Dentate Upper and Lower Jaws: An In Vitro Study
## 4 Discussion
In a recent study, the mean mandibular and maxillary trueness values ranged from 32 to 48 \(\upmu\)m with the iTero Element 5D, which is the latest iTero model generation [41]. The higher mean trueness values of the latest iTero model generation compared to the values of the iTero scanner used in this study were probably caused by the circumstance that natural teeth with filling materials were more difficult to scan. Nonetheless, this highlights that newer model generations do not necessarily produce scans with a higher trueness. An important feature of the TR is that, while scanning, the focal plane is changed in a periodic pattern without changing the scanner's head distance from the scanned object [38]. A high contrast is achieved as every point of the scanned surface is only scanned when the point is in focus and when it shows a maximum level of correlation in the scanner's optical field on the digital sensor. Scanning errors might occur when changing of the focal plane overlaps with changing positions of the operator's arm. This error is supposed to be minimized by a high speed of focal plane changes and very short data acquisition time [42]. The TR showed the highest number of datapoints in maxillary scans in the study at hand and the second highest number of datapoints in mandibular scans. However, the TR also exhibited the second highest number of outliers. Despite a higher number of outliers compared to the IT, CS and TD and non-uniform tessellation, The TR showed the highest overall trueness and precision of all intraoral scanners tested in this study. Nonetheless, there was no statistically significant difference between the overall mean trueness and precision of the TR, IT and CS (\(p<0.05\)). The TR showed significantly less blocked interproximal areas than the other scanner, which used parallel confocal microscopy in this study (IT). A major reason for this might be that the TR is a video-based system, while the IT works with single pictures. Mean trueness values of the TRIOS 3 and 4 in another in vitro study, which also made use of a full arch reference model with unprepared teeth, were higher than with the TRIOS scanner tested in this study [33]. The TRIOS 4 also produced higher mean trueness values in a recent study [41]. Thus, contrary to a study by [PERSON] et al. [21], which used a full arch model with missing and prepared teeth, TRIOS scanners did not show a significant trueness improvement in newer model generations. Despite the need for reflective coating and the risk of uneven powder application, the TD has previously been shown to work very accurately [36; 43; 44]. The TD delivers 3D images in a real-time video sequence by using a blue-LED-light wavefront sampling technique. The image acquisition process required a uniform surface, which was provided by reflective coating with titanium oxide powder. Identical reflecting properties were necessary because light reflections from different angles, like in triangulation-based optical sensors, are focused on optical sensors [36; 45]. The scanner used a rotating device, which is located in the front of the sensor. This device allows images of the same location from different angles and thus works like different cameras taking 2D images of the same object which are computed together to a single 3D picture [46]. Moving mechanical parts like the built-in rotating aperture and incorrectly applied reflective coating were potential sources of error for the scanning process. On the other hand, reflective coating can also increase scanning accuracy because it creates a more uniform reflecting surface than tooth surfaces composed of different materials [29]. The missing interproximal parts of TD scans might be due to insufficient powder application. The reference scanner, however, also needed reflective coating and accurately scanned interproximal areas. Thus, insufficient powder application most likely was not the reason for the insufficient acquisition of interproximal areas with the TD.