# Assessment of Dental Arch Reproduction Quality by Using Traditional and Digital Methods
## 4 Discussion  
Various procedures for measuring digital dental arch models were used, to assess the accuracy of the digital impression method. Superimposing digital models using a 3D analysis program is the most commonly used method to measure and visualize surface deviations between digital models and the reference model [8; 13; 14; 15]. Measuring linear distances between specific points located on the teeth or between reference objects attached to the model is also common practice [16; 17; 18]. Another method of assessing accuracy is scanning calibrated objects which dimensions are known [19] or measuring the marginal fit of final permanent prosthetic restorations [20; 21; 22]. However, these calibrated objects are small and do not have typical morphology of teeth or dental arches. In turn, the restoration fit assessment includes the entire production process, not just the assessment of the preparation scan quality [23]. Some sources of inaccuracy include 3D data registration by digital scanners and data processing by the CAD/CAM software program. The process of milling or printing dental models produces its own inaccuracies but also includes errors that occur at all stages [24]. We made the decision to assess the reproduction of the entire dental arch after printing the models, for this study. In the available literature, most researchers evaluated intraoral scanners by using 3D comparative analysis, measuring only virtual models without producing real master models [8; 13; 14; 15]. Only a few studies compared dimensional error after creating the physical model [25; 26; 27]. Some previous studies were based on only a single tooth, without checking representation of the entire arch [28]. Their clinical value is therefore limited because the authenticity of the reproduction assessed in them cannot be related to more extensive and complicated clinical situations. For single tooth, [PERSON] et al. [29] obtained high values of the trueness of virtual models, due to the examined intraoral scanners with an RMS variable value range from 0.0069 \(\pm\) 0.0009 mm for the TRIOS 2 scanner to 0.0452 \(\pm\) 0.0171 mm in the case of the Omnican camera. In turn, for the entire arch, [PERSON] et al. [30] achieved the trueness of tested intraoral scanners at the level of 0.038 to 0.3329 mm for the model with 14 prepared teeth, while [PERSON] et al. [31] found trueness to vary from 0.0294 to 0.0449 mm. In the present study, traditional methods using impressions with addition silicone material (SGM) ensured the highest trueness (RMS = 0.0424 \(\pm\) 0.0102 mm) in the reproduction of the phantom. Digital methods (TPM) provided lower trueness (RMS = 0.1059 \(\pm\) 0.0041 mm) to a statistically significant degree. In in vitro studies conducted by [PERSON] et al. [26], comparison of models in the Geomagic program did not show statistically significant differences between printed models (SLA), which achieved accuracy at the level of 0.1143 \(\pm\) 0.0018 mm, and gypsum, with value of  
Figure 10: Distribution of absolute values of the V\({}_{\rm LD}\) coefficient for the examined linear dimensions (TPM). 0.11112 \(\pm\) 0.0031 mm. The authors stated that the accuracy value achieved by models printed from photopolymer materials (SLA) is sufficient for clinical applications. Since previous digital model accuracy tests recommended a measurement error of less than 0.2 mm as acceptable in clinical settings [26; 32], the average accuracy of the models printed in this study was 0.1059 mm, indicating their potential for use in clinical settings. Studies focused on full-arch scans using intraoral scanners have found large deviations in the lateral segment of the dental arch on the opposite side to the point where the scan was started [33]. The limited complexity of the front teeth geometry contributes to the accumulation of errors in matching the sequentially captured images [23; 31; 34]. Small errors in this region, especially those affecting angular relationships, add relatively large deviations at the end of the arch [17; 18].