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Korean J Orthod 2021; 51(6): 363-365

Published online November 25, 2021 https://doi.org/10.4041/kjod.2021.51.6.363

Copyright © The Korean Association of Orthodontists.

READER’S FORUM

Seung-Youp Lee

Department of Orthodontics, School of Dentistry, Jeonbuk National University, Iksan, Korea

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Miran Kwon, Youngmok Cho, Dong-Wook Kim, MyungSu Kim, Yoon-Ji Kim, Minho Chang

Full-arch accuracy of five intraoral scanners: In vivo analysis of trueness and precision.

- Korean J Orthod 2021;51:95-104

I appreciate the authors’ work to investigate the full-arch accuracy of five intraoral scanners. For better understanding, I would like to ask some questions.

Q1. In this article, the main key issue was the concept of trueness and precision. Would you explain in more detail about the concept of trueness and precision in analysis of the scanners?

Q2. You compared five scanners in this article. In capturing data, were there any technical differences among them in terms of the possibility of errors?

Q3. I thankfully read your article for reference of each scanners. Did you have any comforts or disturbances in manipulating each scanner? If you experienced anything worthwhile, would you advise for readers.

Questioned by

Seung-Youp Lee

Department of Orthodontics, School of Dentistry, Jeonbuk National University, Iksan, Korea

A1. The trueness and precision of the scanners were analyzed by measuring linear distances of the full-arch scan data acquired from the scanners. Four reference spheres were placed in the dental arch (two in the canines and two in the molars), and the distance between the spheres was analyzed (Figure 1). Using the distance between the spheres instead of the tooth’s anatomic landmarks minimizes measurement errors because the Geomagic Control X software (version 2018.1.1; Evatronix SA, Bielsko-Biala, Poland) that was used in the study automatically detects the spheres and calculates the distance between the centers of the spheres; thus, minimizing the error from positioning the anatomic landmarks, such as the cusp tip. Trueness indicates the difference between the intra-arch linear measurements acquired from the intraoral scan data and those from the extraoral industrial-grade scanner, which was the reference scanner. The industrial scanner has an accuracy of 7 µm and served as the “truth.” Precision was analyzed by calculating the mean pairwise difference from the five repeated scans per scanner. Tables 1 and 2 display the raw data for trueness and precision acquired from the scan data of a patient using an i500 scanner (Medit Corp., Seoul, Korea), respectively.

Table 1 . Sample raw data for trueness acquired from one patient (Pt) using an i500 scanner (mm)

Distance 123456
Reference (A)*15.75039.76245.20029.44939.14614.322
Actual value (B)Pt1_i500 (1)15.78239.90745.41829.54139.28514.334
Pt1_i500 (2)15.76339.80045.24529.48139.19314.348
Pt1_i500 (3)15.74139.78345.22029.40839.09114.324
Pt1_i500 (4)15.77339.82945.13229.47139.07614.355
Pt1_i500 (5)15.77139.85145.35329.48639.23014.346
Deviation (B-A)Pt1_i500 (1)0.0320.1460.2180.0920.1390.011
Pt1_i500 (2)0.0130.0380.0450.0320.0470.026
Pt1_i500 (3)−0.0090.0220.019−0.041−0.0550.002
Pt1_i500 (4)0.0230.067−0.0680.022−0.0700.033
Pt1_i500 (5)0.0210.0890.1520.0370.0840.024

For each patient, distances were measured for each of the five scans [(1)–(5)] performed per scanner. Then, the difference between the distance measured from the reference scan and the intraoral scan was calculated. Mean absolute distances were regarded as the trueness for the scanner.

1, distance between reference spheres 1 and 2; 2, distance between reference spheres 1 and 3; 3, distance between reference spheres 1 and 4; 4, distance between reference spheres 2 and 3; 5, distance between reference spheres 2 and 4; 6, distance between reference spheres 3 and 4.

*Indicates the distance measured from the scans taken with the industrial scanner (Solutionix C500; Medit Corp., Seoul, Korea).

Indicates the distance measured from the intraoral scanner (i500; Medit Corp.).

Indicates the difference between the distance measured from the industrial scanner and the intraoral scanner.



Table 2 . Sample raw data for precision acquired from one patient using an i500 scanner (mm)

Distance123456
Difference between scans
(1), (2)−0.021−0.091−0.146−0.062−0.0980.002
(1), (3)−0.004−0.070−0.112−0.024−0.045−0.007
(1), (4)−0.005−0.097−0.168−0.045−0.0820.004
(1), (5)−0.0890.0180.0180.004−0.002−0.002
(2), (3)0.0170.0210.0350.0390.053−0.009
(2), (4)0.016−0.006−0.0220.0170.0160.003
(2), (5)0.0200.1090.1650.0660.096−0.003
(3), (4)−0.009−0.027−0.057−0.022−0.0370.011
(3), (5)0.0030.0890.1300.0270.0430.006
(4), (5)0.0040.1150.1870.0490.080−0.006

Pairwise differences from the five repeated scans [(1)–(5)] were calculated and the mean was regarded as the precision of the scanner for the patient.

1, distance between reference spheres 1 and 2; 2, distance between reference spheres 1 and 3; 3, distance between reference spheres 1 and 4; 4, distance between reference spheres 2 and 3; 5, distance between reference spheres 2 and 4; 6, distance between reference spheres 3 and 4.



Figure 1. Measurement of linear distances. Linear distances between spheres are automatically calculated by matching with pre-imputed specification data.
Distance 1, between reference spheres 1 and 2; Distance 2, between reference spheres 1 and 3; Distance 3, between reference spheres 1 and 4; Distance 4, between reference spheres 2 and 3; Distance 5, between reference spheres 2 and 4; Distance 6, between reference spheres 3 and 4.

A2. There were statistically significant differences in trueness and precision among the five scanners for certain measured distances (Table 3). We believe that scanning technology, such as confocal microscopy (Trios; 3Shape A/S, Copenhagen, Denmark/iTero; Align Technology, Inc., San Jose, CA, USA) and optical triangulation (i500/Omnicam; Dentsply Sirona, York, PA, USA/CS3600; Carestream Health, Rochester, NY, USA), is a major factor associated with scanner accuracy. A systematic review of intraoral scanner accuracy has also shown that there is a difference in accuracy according to intraoral scanner technologies, and a meta-analysis showed that Trios is more accurate than Omnicam in both trueness and precision.1 Moreover, the scan accuracy is also affected by the scan strategy.2-4 Therefore, it is important to scan the arch according to the manufacturer’s instructions. Other factors associated with the scan data accuracy are scanner software versions,5,6 ambient lights,7 and scanning skills.8 In our study, an intraoral scan was performed following the manufacturer’s instructions to minimize errors during data capturing.

Table 3 . Tests of fixed effects

EffectNumerator DFDenominator DFF
value
p-value
Distance5185140.3< 0.0001
Scanner type4371.130.357
Distance × Scanner type201851.660.044

DF, degrees of freedom.



A3. Regarding manipulations, the scanner head should be small, light-weight, and ergonomic in design. Personally, I prefer a pod-type scanner to a gun-type scanner. iTero has a heavy (approximately 500 g) and large scanner head that makes it difficult when scanning patients who have limited mouth opening or temporomandibular joint issues. However, it has advanced software features such as automated tooth setup and tooth movement tracking features. Medit’s i500 also has an automated tooth setup function that may be used for patient consultations. i500 has the lightest scanner head (280 g). The Omnicam scanner has a solid build and the scanner head is small. The Trios scanner has the highest accuracy. The accuracy for a full arch scan of the studied intraoral scanners was clinically acceptable for orthodontic treatments, such as virtual setup and clear aligner therapy. However, for prosthodontic treatment, such as long-span fixed partial dentures, errors ranging from 200–300 µm can be problematic.9

Replied by

Yoon-Ji Kim

Department of Orthodontics, Asan Medical Center, University of Ulsan School of Medicine, Seoul, Korea

  1. Kachhara S, Nallaswamy D, Ganapathy DM, Sivaswamy V, Rajaraman V. Assessment of intraoral scanning technology for multiple implant impressions - a systematic review and meta-analysis. J Indian Prosthodont Soc 2020;20:141-52.
    Pubmed KoreaMed CrossRef
  2. Müller P, Ender A, Joda T, Katsoulis J. Impact of digital intraoral scan strategies on the impression accuracy using the TRIOS Pod scanner. Quintessence Int 2016;47:343-9.
  3. Medina-Sotomayor P, Pascual-Moscardó A, Camps I. Accuracy of four digital scanners according to scanning strategy in complete-arch impressions. PLoS One 2018;13:e0202916.
    Pubmed KoreaMed CrossRef
  4. Oh KC, Park JM, Moon HS. Effects of scanning strategy and scanner type on the accuracy of intraoral scans: a new approach for assessing the accuracy of scanned data. J Prosthodont 2020;29:518-23.
    Pubmed CrossRef
  5. Haddadi Y, Bahrami G, Isidor F. Effect of software version on the accuracy of an intraoral scanning device. Int J Prosthodont 2018;31:375-6.
    Pubmed CrossRef
  6. Schmidt A, Schlenz MA, Liu H, Kämpe HS, Wöstmann B. The influence of hard- and software improvement of intraoral scanners on the implant transfer accuracy from 2012 to 2021: an in vitro study. Appl Sci 2021;11:7166.
    CrossRef
  7. Revilla-León M, Subramanian SG, Özcan M, Krishnamurthy VR. Clinical study of the influence of ambient light scanning conditions on the accuracy (trueness and precision) of an intraoral scanner. J Prosthodont 2020;29:107-13.
    Pubmed CrossRef
  8. Lim JH, Park JM, Kim M, Heo SJ, Myung JY. Comparison of digital intraoral scanner reproducibility and image trueness considering repetitive experience. J Prosthet Dent 2018;119:225-32.
    Pubmed CrossRef
  9. Waldecker M, Rues S, Rammelsberg P, Bömicke W. Accuracy of complete-arch intraoral scans based on confocal microscopy versus optical triangulation: a comparative in vitro study. J Prosthet Dent 2021;126:414-20.
    Pubmed CrossRef

Article

Reader's Forum

Korean J Orthod 2021; 51(6): 363-365

Published online November 25, 2021 https://doi.org/10.4041/kjod.2021.51.6.363

Copyright © The Korean Association of Orthodontists.

READER’S FORUM

Seung-Youp Lee

Department of Orthodontics, School of Dentistry, Jeonbuk National University, Iksan, Korea

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Body

Miran Kwon, Youngmok Cho, Dong-Wook Kim, MyungSu Kim, Yoon-Ji Kim, Minho Chang

Full-arch accuracy of five intraoral scanners: In vivo analysis of trueness and precision.

- Korean J Orthod 2021;51:95-104

Body

I appreciate the authors’ work to investigate the full-arch accuracy of five intraoral scanners. For better understanding, I would like to ask some questions.

Q1. In this article, the main key issue was the concept of trueness and precision. Would you explain in more detail about the concept of trueness and precision in analysis of the scanners?

Q2. You compared five scanners in this article. In capturing data, were there any technical differences among them in terms of the possibility of errors?

Q3. I thankfully read your article for reference of each scanners. Did you have any comforts or disturbances in manipulating each scanner? If you experienced anything worthwhile, would you advise for readers.

Questioned by

Seung-Youp Lee

Department of Orthodontics, School of Dentistry, Jeonbuk National University, Iksan, Korea

Body

A1. The trueness and precision of the scanners were analyzed by measuring linear distances of the full-arch scan data acquired from the scanners. Four reference spheres were placed in the dental arch (two in the canines and two in the molars), and the distance between the spheres was analyzed (Figure 1). Using the distance between the spheres instead of the tooth’s anatomic landmarks minimizes measurement errors because the Geomagic Control X software (version 2018.1.1; Evatronix SA, Bielsko-Biala, Poland) that was used in the study automatically detects the spheres and calculates the distance between the centers of the spheres; thus, minimizing the error from positioning the anatomic landmarks, such as the cusp tip. Trueness indicates the difference between the intra-arch linear measurements acquired from the intraoral scan data and those from the extraoral industrial-grade scanner, which was the reference scanner. The industrial scanner has an accuracy of 7 µm and served as the “truth.” Precision was analyzed by calculating the mean pairwise difference from the five repeated scans per scanner. Tables 1 and 2 display the raw data for trueness and precision acquired from the scan data of a patient using an i500 scanner (Medit Corp., Seoul, Korea), respectively.

Table 1 . Sample raw data for trueness acquired from one patient (Pt) using an i500 scanner (mm).

Distance 123456
Reference (A)*15.75039.76245.20029.44939.14614.322
Actual value (B)Pt1_i500 (1)15.78239.90745.41829.54139.28514.334
Pt1_i500 (2)15.76339.80045.24529.48139.19314.348
Pt1_i500 (3)15.74139.78345.22029.40839.09114.324
Pt1_i500 (4)15.77339.82945.13229.47139.07614.355
Pt1_i500 (5)15.77139.85145.35329.48639.23014.346
Deviation (B-A)Pt1_i500 (1)0.0320.1460.2180.0920.1390.011
Pt1_i500 (2)0.0130.0380.0450.0320.0470.026
Pt1_i500 (3)−0.0090.0220.019−0.041−0.0550.002
Pt1_i500 (4)0.0230.067−0.0680.022−0.0700.033
Pt1_i500 (5)0.0210.0890.1520.0370.0840.024

For each patient, distances were measured for each of the five scans [(1)–(5)] performed per scanner. Then, the difference between the distance measured from the reference scan and the intraoral scan was calculated. Mean absolute distances were regarded as the trueness for the scanner..

1, distance between reference spheres 1 and 2; 2, distance between reference spheres 1 and 3; 3, distance between reference spheres 1 and 4; 4, distance between reference spheres 2 and 3; 5, distance between reference spheres 2 and 4; 6, distance between reference spheres 3 and 4..

*Indicates the distance measured from the scans taken with the industrial scanner (Solutionix C500; Medit Corp., Seoul, Korea)..

Indicates the distance measured from the intraoral scanner (i500; Medit Corp.)..

Indicates the difference between the distance measured from the industrial scanner and the intraoral scanner..



Table 2 . Sample raw data for precision acquired from one patient using an i500 scanner (mm).

Distance123456
Difference between scans
(1), (2)−0.021−0.091−0.146−0.062−0.0980.002
(1), (3)−0.004−0.070−0.112−0.024−0.045−0.007
(1), (4)−0.005−0.097−0.168−0.045−0.0820.004
(1), (5)−0.0890.0180.0180.004−0.002−0.002
(2), (3)0.0170.0210.0350.0390.053−0.009
(2), (4)0.016−0.006−0.0220.0170.0160.003
(2), (5)0.0200.1090.1650.0660.096−0.003
(3), (4)−0.009−0.027−0.057−0.022−0.0370.011
(3), (5)0.0030.0890.1300.0270.0430.006
(4), (5)0.0040.1150.1870.0490.080−0.006

Pairwise differences from the five repeated scans [(1)–(5)] were calculated and the mean was regarded as the precision of the scanner for the patient..

1, distance between reference spheres 1 and 2; 2, distance between reference spheres 1 and 3; 3, distance between reference spheres 1 and 4; 4, distance between reference spheres 2 and 3; 5, distance between reference spheres 2 and 4; 6, distance between reference spheres 3 and 4..



Figure 1. Measurement of linear distances. Linear distances between spheres are automatically calculated by matching with pre-imputed specification data.
Distance 1, between reference spheres 1 and 2; Distance 2, between reference spheres 1 and 3; Distance 3, between reference spheres 1 and 4; Distance 4, between reference spheres 2 and 3; Distance 5, between reference spheres 2 and 4; Distance 6, between reference spheres 3 and 4.

A2. There were statistically significant differences in trueness and precision among the five scanners for certain measured distances (Table 3). We believe that scanning technology, such as confocal microscopy (Trios; 3Shape A/S, Copenhagen, Denmark/iTero; Align Technology, Inc., San Jose, CA, USA) and optical triangulation (i500/Omnicam; Dentsply Sirona, York, PA, USA/CS3600; Carestream Health, Rochester, NY, USA), is a major factor associated with scanner accuracy. A systematic review of intraoral scanner accuracy has also shown that there is a difference in accuracy according to intraoral scanner technologies, and a meta-analysis showed that Trios is more accurate than Omnicam in both trueness and precision.1 Moreover, the scan accuracy is also affected by the scan strategy.2-4 Therefore, it is important to scan the arch according to the manufacturer’s instructions. Other factors associated with the scan data accuracy are scanner software versions,5,6 ambient lights,7 and scanning skills.8 In our study, an intraoral scan was performed following the manufacturer’s instructions to minimize errors during data capturing.

Table 3 . Tests of fixed effects.

EffectNumerator DFDenominator DFF
value
p-value
Distance5185140.3< 0.0001
Scanner type4371.130.357
Distance × Scanner type201851.660.044

DF, degrees of freedom..



A3. Regarding manipulations, the scanner head should be small, light-weight, and ergonomic in design. Personally, I prefer a pod-type scanner to a gun-type scanner. iTero has a heavy (approximately 500 g) and large scanner head that makes it difficult when scanning patients who have limited mouth opening or temporomandibular joint issues. However, it has advanced software features such as automated tooth setup and tooth movement tracking features. Medit’s i500 also has an automated tooth setup function that may be used for patient consultations. i500 has the lightest scanner head (280 g). The Omnicam scanner has a solid build and the scanner head is small. The Trios scanner has the highest accuracy. The accuracy for a full arch scan of the studied intraoral scanners was clinically acceptable for orthodontic treatments, such as virtual setup and clear aligner therapy. However, for prosthodontic treatment, such as long-span fixed partial dentures, errors ranging from 200–300 µm can be problematic.9

Replied by

Yoon-Ji Kim

Department of Orthodontics, Asan Medical Center, University of Ulsan School of Medicine, Seoul, Korea

Fig 1.

Figure 1.Measurement of linear distances. Linear distances between spheres are automatically calculated by matching with pre-imputed specification data.
Distance 1, between reference spheres 1 and 2; Distance 2, between reference spheres 1 and 3; Distance 3, between reference spheres 1 and 4; Distance 4, between reference spheres 2 and 3; Distance 5, between reference spheres 2 and 4; Distance 6, between reference spheres 3 and 4.
Korean Journal of Orthodontics 2021; 51: 363-365https://doi.org/10.4041/kjod.2021.51.6.363

Table 1 . Sample raw data for trueness acquired from one patient (Pt) using an i500 scanner (mm).

Distance 123456
Reference (A)*15.75039.76245.20029.44939.14614.322
Actual value (B)Pt1_i500 (1)15.78239.90745.41829.54139.28514.334
Pt1_i500 (2)15.76339.80045.24529.48139.19314.348
Pt1_i500 (3)15.74139.78345.22029.40839.09114.324
Pt1_i500 (4)15.77339.82945.13229.47139.07614.355
Pt1_i500 (5)15.77139.85145.35329.48639.23014.346
Deviation (B-A)Pt1_i500 (1)0.0320.1460.2180.0920.1390.011
Pt1_i500 (2)0.0130.0380.0450.0320.0470.026
Pt1_i500 (3)−0.0090.0220.019−0.041−0.0550.002
Pt1_i500 (4)0.0230.067−0.0680.022−0.0700.033
Pt1_i500 (5)0.0210.0890.1520.0370.0840.024

For each patient, distances were measured for each of the five scans [(1)–(5)] performed per scanner. Then, the difference between the distance measured from the reference scan and the intraoral scan was calculated. Mean absolute distances were regarded as the trueness for the scanner..

1, distance between reference spheres 1 and 2; 2, distance between reference spheres 1 and 3; 3, distance between reference spheres 1 and 4; 4, distance between reference spheres 2 and 3; 5, distance between reference spheres 2 and 4; 6, distance between reference spheres 3 and 4..

*Indicates the distance measured from the scans taken with the industrial scanner (Solutionix C500; Medit Corp., Seoul, Korea)..

Indicates the distance measured from the intraoral scanner (i500; Medit Corp.)..

Indicates the difference between the distance measured from the industrial scanner and the intraoral scanner..


Table 2 . Sample raw data for precision acquired from one patient using an i500 scanner (mm).

Distance123456
Difference between scans
(1), (2)−0.021−0.091−0.146−0.062−0.0980.002
(1), (3)−0.004−0.070−0.112−0.024−0.045−0.007
(1), (4)−0.005−0.097−0.168−0.045−0.0820.004
(1), (5)−0.0890.0180.0180.004−0.002−0.002
(2), (3)0.0170.0210.0350.0390.053−0.009
(2), (4)0.016−0.006−0.0220.0170.0160.003
(2), (5)0.0200.1090.1650.0660.096−0.003
(3), (4)−0.009−0.027−0.057−0.022−0.0370.011
(3), (5)0.0030.0890.1300.0270.0430.006
(4), (5)0.0040.1150.1870.0490.080−0.006

Pairwise differences from the five repeated scans [(1)–(5)] were calculated and the mean was regarded as the precision of the scanner for the patient..

1, distance between reference spheres 1 and 2; 2, distance between reference spheres 1 and 3; 3, distance between reference spheres 1 and 4; 4, distance between reference spheres 2 and 3; 5, distance between reference spheres 2 and 4; 6, distance between reference spheres 3 and 4..


Table 3 . Tests of fixed effects.

EffectNumerator DFDenominator DFF
value
p-value
Distance5185140.3< 0.0001
Scanner type4371.130.357
Distance × Scanner type201851.660.044

DF, degrees of freedom..


References

  1. Kachhara S, Nallaswamy D, Ganapathy DM, Sivaswamy V, Rajaraman V. Assessment of intraoral scanning technology for multiple implant impressions - a systematic review and meta-analysis. J Indian Prosthodont Soc 2020;20:141-52.
    Pubmed KoreaMed CrossRef
  2. Müller P, Ender A, Joda T, Katsoulis J. Impact of digital intraoral scan strategies on the impression accuracy using the TRIOS Pod scanner. Quintessence Int 2016;47:343-9.
  3. Medina-Sotomayor P, Pascual-Moscardó A, Camps I. Accuracy of four digital scanners according to scanning strategy in complete-arch impressions. PLoS One 2018;13:e0202916.
    Pubmed KoreaMed CrossRef
  4. Oh KC, Park JM, Moon HS. Effects of scanning strategy and scanner type on the accuracy of intraoral scans: a new approach for assessing the accuracy of scanned data. J Prosthodont 2020;29:518-23.
    Pubmed CrossRef
  5. Haddadi Y, Bahrami G, Isidor F. Effect of software version on the accuracy of an intraoral scanning device. Int J Prosthodont 2018;31:375-6.
    Pubmed CrossRef
  6. Schmidt A, Schlenz MA, Liu H, Kämpe HS, Wöstmann B. The influence of hard- and software improvement of intraoral scanners on the implant transfer accuracy from 2012 to 2021: an in vitro study. Appl Sci 2021;11:7166.
    CrossRef
  7. Revilla-León M, Subramanian SG, Özcan M, Krishnamurthy VR. Clinical study of the influence of ambient light scanning conditions on the accuracy (trueness and precision) of an intraoral scanner. J Prosthodont 2020;29:107-13.
    Pubmed CrossRef
  8. Lim JH, Park JM, Kim M, Heo SJ, Myung JY. Comparison of digital intraoral scanner reproducibility and image trueness considering repetitive experience. J Prosthet Dent 2018;119:225-32.
    Pubmed CrossRef
  9. Waldecker M, Rues S, Rammelsberg P, Bömicke W. Accuracy of complete-arch intraoral scans based on confocal microscopy versus optical triangulation: a comparative in vitro study. J Prosthet Dent 2021;126:414-20.
    Pubmed CrossRef