## 4 Discussion
Our trueness analysis revealed that the accuracy of position reproduction was affected when the implant placement depth was at least 4.5 mm. [PERSON] et al. [17] showed a similar trend, concluding that the accuracy of digital impressions was not affected when implants were placed in the model at 0 mm, 2 mm, and 4 mm, and the ISB is attached. When the exposed length of the ISB was sufficient, a small change in that length did not significantly affect the accuracy. On the other hand, when assessingimage matching according to the exposed length of the ISB, [PERSON] et al. [24] found that for exposed lengths of the ISB of full exposure, 0.5 mm less exposure, 1.0 mm less exposure, 1.5 mm less exposure, 2.0 mm less exposure and 2.5 mm less exposure, the RMS values increased to 16.1 \(\pm\) 1.1 \(\upmu\)m, 93.4 \(\pm\) 0.8 \(\upmu\)m, 158.6 \(\pm\) 1.2 \(\upmu\)m, 300.4 \(\pm\) 1.0 \(\upmu\)m, 606.2 \(\pm\) 1.3 \(\upmu\)m, and 948.4 \(\pm\) 8.4 \(\upmu\)m, respectively, which differed from the results of the present study. This may be due to differences in the designs of the study models used in the experiments, scanning technologies, types of ISB used, algorithm modification methods, and other applied scanning protocols. The overall deviations of trueness obtained using the CS3600 scanner were 27.0 \(\pm\) 10.4 \(\upmu\)m, 24.7 \(\pm\) 6.8 \(\upmu\)m, and 23.7 \(\pm\) 15.8 \(\upmu\)m at the lateral incisor, first premolar, and first molar, respectively, when the implant was placed at the bone level. [PERSON] et al. [38] found a similar accuracy of 24.8 \(\pm\) 4.6 \(\upmu\)m, and that the RMS tended to increase as the implant depth increased to 4.5 mm and 6.0 mm. The RMS value for precision obtained using the TRIOS 3 scanner was 23.1 \(\pm\) 10.2 \(\upmu\)m at the first premolar when the implant was placed at the bone level, and 25.1 \(\pm\) 12.4 \(\upmu\)m at the first molar, which were similar to the findings of [PERSON] et al. The study also analyzed the precision of implant digital impression using a PEEK ISB made in the shape of a unilateral implant cylinder, and found an RMS value of 24.5 \(\pm\) 3.7 \(\upmu\)m. However, in the present study, the accuracy at the position of the lateral incisor was found to decrease significantly, showing a higher RMS value of 38.2 \(\pm\) 20.0 \(\upmu\)m.  
The errors found in this study when digital impressions were acquired while the exposed length of the ISB was insufficient can be considered high from a clinical standpoint. An error occurring in the first impression-taking step during the process of manufacturing a prosthesis may affect the accuracy of the implant prosthesis. This study has demonstrated that the exposed length of the ISB connected for digital impression acquisition can affect the positional reproducibility of the implant abutment. It was found that the precision was affected when the implant was submerged by at least 3.0 mm, while the trueness was affected for a submersion of at least 4.5 mm. The study results can be utilized when formulating a guideline on the accuracy of implant position reproduction according to various implant placement depths, implant positions, and types of oral scanners when fabricating implant prostheses with an oral scanner in clinical practice. If the exposed length of the ISB is insufficient when it is being scanned using the digital impression-taking technique in clinical practice, considering the level of the implant, the impression should instead be obtained using the conventional technique. Additionally, it was confirmed that even if an impression is obtained using conventional techniques, if the impression is digitized indirectly with a tabletop scanner, the errors that occur will vary with the exposed length of the ISB. Therefore, extra caution is needed in the digital prosthesis production workflow. Rather than connecting the ISB directly to the fixture, the accuracy can be increased by connecting a component of a supragingival level using a stock abutment or a multiunit abutment first and then performing a digital scan with an ISB.