Comparison of two intraoral scanners based on three-dimensional surface analysis
Lee Progress in Orthodontics
Comparison of two intraoral scanners based on three-dimensional surface analysis
Kyung-Min Lee 0
0 Department of Orthodontics, School of Dentistry, Chonnam National University , 33 Yongbong-ro, Buk-gu, Gwangju 61186 , South Korea
Background: This in vivo study evaluated the difference of two well-known intraoral scanners used in dentistry, namely iTero (Align Technology) and TRIOS (3Shape). Methods: Thirty-two participants underwent intraoral scans with TRIOS and iTero scanners, as well as conventional alginate impressions. The scans obtained with the two intraoral scanners were compared with each other and were also compared with the corresponding model scans by means of three-dimensional surface analysis. The average differences between the two intraoral scans on the surfaces were evaluated by color-mapping. The average differences in the three-dimensional direction between each intraoral scans and its corresponding model scan were calculated at all points on the surfaces. Results: The average differences between the two intraoral scanners were 0.057 mm at the maxilla and 0.069 mm at the mandible. Color histograms showed that local deviations between the two scanners occurred in the posterior area. As for difference in the three-dimensional direction, there was no statistically significant difference between two scanners. Conclusions: Although there were some deviations in visible inspection, there was no statistical significance between the two intraoral scanners.
Intraoral scan; Three-dimensional surface analysis; Digital impression
With the advances in computer technology, digital
dental models are now being widely used for orthodontic
diagnosis and treatment planning. The use of digital
models alleviates many of the challenges posed by
plaster models made from conventional impressions, which
include the burden of storage, the risk of damage or
breakage, and the difficulties in sharing the data with
other clinicians involved in the patients’ care [
Digital dental models can be created through either
indirect or direct techniques. Indirect methods involve
laser scanning or computed tomographic imaging of the
alginate impressions or plaster models, and direct
methods involve intraoral scanners. With the
introduction of chairside intraoral scanners, interest in obtaining
digital dental model using the direct method has
After the introduction of computer-aided
design/computer-aided manufacturing (CAD/CAM) concepts into
dental applications by Dr. Francois Duret at the Chicago
Midwinter Meeting in 1989 [
], several intraoral
scanners have been introduced. Recently, a few intraoral
scanners have been released on the market, including
the iTero (Align Technologies), TRIOS (3Shape), True
Definition (3M ESPE), CEREC Omnicam (Sirona), and
CS 3600 (Carestream Dental) [
The accuracy of intraoral scanners has been evaluated
for both single abutment [
] and short-span fixed
dental prostheses [
]. To determine the accuracy of
intraoral scanners, researchers have performed in vitro
studies using reference models [
shortspan intraoral scans have exhibited excellent accuracy,
few in vivo studies have investigated the accuracy of
intraoral scans on whole dentition in the clinical setting.
Kuhr et al. [
] developed a new method of measuring
the trueness of full-arch intraoral scans using reference
spheres. However, the authors investigated only lower
]. Anh et al. [
] compared the precision of
images acquired using the iTero and TRIOS intraoral
scanners; however, they performed in vitro studies using
fabricated dental arch models.
The iTero and TRIOS scanners allow full-arch
scanning and do not require powdering of the tooth surfaces.
Moreover, these two scanners have incorporated the
orthodontic application software within the scanners. To
our knowledge, iTero and TRIOS are the two
bestknown commercially available intraoral scanners in
dentistry; therefore, it is important to compare their relative
scanning accuracy (Table 1). We cannot assume that all
intraoral scanners will produce the same level of
clinically acceptable results, and it would be beneficial to see
how the measurements compare between different
scanners. With this in mind, the present study aimed to
compare the scanning results of the iTero and TRIOS
Thirty-two participants were enrolled in the study after
providing informed consent. This study was approved by
the Institutional Review Board for Medical Science at
the Chonnam National University Hospital, Gwangju,
Korea (CNUDH-2015-003). The inclusion criteria were
complete permanent dentition, with no missing tooth
and no crown or bridge restoration. In addition,
participants with moderate or severe crowding and dentofacial
deformity were excluded from this study.
Intraoral scanning with TRIOS and iTero
Intraoral scans of 32 participants were included in the
present study. Each participant underwent intraoral
scanning with TRIOS (3Shape, Copenhagen, Denmark)
and iTero (version 4.0; Align Technology, San Jose, CA),
as well as alginate impression. All intraoral scans with
the iTero and TRIOS scanners were recorded by a single
examiner. The scanners were calibrated every 8 days
according to the manufacturers’ recommendation. TRIOS
scanning was performed following the instructions of
the manufacturer. In brief, the scanning was started
from the left side and continued to the right side along
the occlusion. After the occlusal surfaces were scanned,
lingual and buccal surface scans were performed. In the
upper arch, the occlusal surfaces were scanned first, in
the same manner as in the lower arch, whereas the
buccal and lingual surfaces were scanned in order. When
scanning the occlusal surfaces, the scanner head was
kept at 0–5 mm from the tooth. For the scanning of the
buccal and lingual surfaces, the scanner tip was rolled
45°–90° to the buccal and lingual sides, respectively. The
image could be continuously viewed on a screen during
the scanning process, which allowed direct visual
feedback to ensure that no areas were missed. After
scanning, all scan data were sent to the OrthoAnalyzer™
(3Shape, Copenhagen, Denmark) software program,
where they were reprocessed as a stereolithography
(STL) file. The iTero scanning was performed in a
predetermined sequence. The mandibular left area was
scanned from the second molar to the incisor. The
mandibular right area was scanned from the second molar.
In the maxilla, the right quadrant was scanned first. The
scan data were reprocessed as an STL file.
Conventional alginate impression taking
Alginate impressions (Cavex Normal set; Cavex Holland
BV, Haarlem, The Netherlands) for the maxilla and
mandible were taken in a metal tray. Each impression was
rinsed with tap water and disinfected via spraying
(CONTINU Dental Impression Disinfectant, Premium
Plus, Bournemouth, UK). After disinfection, the
impression was directly poured with dental stone. The stone
casts were stored for 5–7 days at a temperature of 23 °C
± 1 °C and humidity of 40% ± 10%. The dental models
were scanned with a laboratory scanner (Orapix, Seoul,
Korea). By means of a reverse engineering software
program (Rapidform 2006; 3D Systems, Rock Hill, SC), the
laboratory-scanned file was converted to STL format.
The adjacent gingival tissue was deleted along the
margin of the clinical crown to allow accurate best-fit
alignment of the crowns.
Comparison of the two intraoral scanners based on
threedimensional surface analysis
The scanning results were compared by using
threedimensional analysis with “shell/shell deviation” software
commands regarding the average surface differences
with subsequent color-coded charts. Two intraoral scans
were registered by using the software’s best-fit algorithm,
and overall, three-dimensional comparisons were
performed. Since the presence of adjacent soft tissue could
increase the range of error, these areas were deleted,
along with the gingival margin, to allow superimposition
of the clinical crowns. The initial registration involved
the selection of three corresponding points on each of
the two intraoral scans. Subsequently, automatic fine
registration was used to finalize the registration (Fig. 1).
The average deviations between the two intraoral scans
at all points on the surfaces were computed by using the
“shell/shell deviation” function in the program. To
remove outlier values, the calculation tolerance value in
the program was set at 1.0 mm [
]. In addition, the
differences between the two scans were evaluated by means
of color histograms.
Deviations in the three-dimensional direction were
also calculated in the incisor and molar regions. Three
reference points were selected, and the point-to-point
distance between each point on the intraoral scan and
the corresponding laser-scanned model was computed.
As for the reference points, the midpoint between the
central incisors and mesiolingual cusp tip of the right
and left first molars was determined. The point-to-point
distance was regarded as the displacement of the
intraoral scan to the laser-scanned model, and the
relative distance between each intraoral scan and
laserscanned model was calculated. In addition, the means
Fig. 2 Discrepancies in the three-dimensional direction were calculated in the incisor and molar regions. Three reference points were selected,
and the point-to-point distance between each point on the intraoral scan and the corresponding model scan was computed. The point-to-point
distance was regarded as the displacement of the intraoral scan to the model scan, and the relative distance was calculated
and standard deviations were computed for each X-, Y-,
and Z-coordinate direction to evaluate which direction
of the discrepancy contributed to the degree of overall
discrepancies (Fig. 2). In order to analyze the differences
between the two intraoral scanners, the paired t test was
used to compare the values using SPSS software package
(version 23.0; SPSS Inc., Chicago, IL).
The average deviations between the two intraoral scans
were 0.057 mm in the maxilla and 0.069 mm in the
mandible (Table 2). The color histogram showed that local
deviations between the two scanners occurred in the
posterior area (Fig. 3). In the three-dimensional deviations,
the intraoral scans presented a minor displacement to the
models; however, there were no statistically significant
differences between the two scanners (Table 3).
The average deviations between the two intraoral
scanners were within 0.07 mm. There is no clear consensus
regarding the clinically or medico-legally acceptable
amount of error in clinical orthodontics. Many
researchers have suggested what they consider to be a
clinically significant difference. Hirogaki et al. [
that orthodontic study models’ accuracy should be about
0.30 mm, while Schirmer and Wiltshire [
that a measurement difference of less than 0.20 mm was
clinically acceptable and Bell et al. [
] suggested that a
measurement difference within 0.27 mm was clinically
insignificant. With regard to the previous studies on the
clinical acceptability in plaster models, the differences
between two scanners of less than 0.07 mm in our
results indicate that both intraoral scanners can be used in
clinical orthodontics. Vasudavan et al. [
intraoral scanning and conventional impression
techniques for fabrication of orthodontic retainers. The
clinical acceptability of retainers did not differ significantly
by fabrication method, and the authors concluded that
digital scans were considered acceptable [
Interestingly, the retainers made from digital scans were
preferred significantly more often by the orthodontist than
those made from alginate impressions.
In the present study, errors in the plaster model
manufacturing process should be taken into
consideration. Although alginate impression has potential errors,
it is still being used for fabricating a diagnostic model.
As plaster model and intraoral scan are used together in
the clinics, it is necessary to evaluate the agreement
between alginate impression and intraoral scanner.
Confocal laser scanning microscopy is used for
intraoral scanner systems [
]. This technique is used to
P values were obtained from paired t test. X, Y, and Z directions indicate mediolateral, superoinferior, and anteroposterior directions, respectively.
SD standard deviation
*In the maxilla, positive value in the X, Y, and Z directions indicates medial, apical, and anterior displacement
†In the maxilla, negative value in the X, Y, and Z directions indicates buccal, occlusal, and posterior displacement
‡In the maxilla, negative value in the X, Y, and Z directions indicates palatal, occlusal, and posterior displacement
§In the mandible, negative value in the X, Y, and Z directions indicates lateral, apical, and lingual displacement
∥In the mandible, positive value in the X, Y, and Z directions indicates lingual, occlusal, and anterior displacement
¶In the mandible, positive value in the X, Y, and Z directions indicates buccal, occlusal, and anterior displacement
acquire in-focus images from selected depths, a process
known as optical sectioning (high-resolution optical
images with depth selectivity) [
]. The iTero scanner
employs a parallel confocal imaging technique with an
array of incident red laser beams [
]. It is important to
maintain the scanning wand at a certain focal distance
while scanning. The TRIOS intraoral system also works
according to the principle of confocal microscopy, with
a fast scanning time. A fundamental characteristic of the
TRIOS system is the variation of the focal plane without
moving the scanner toward the subject being scanned
]. The TRIOS system has the feature of telecentricity
in the space of the subject being scanned, and it is
possible to shift the focal plane while keeping
telecentricity and magnification ratio [
]. We evaluated the light
wave of the iTero and TRIOS scanners using
polarization beam splitter and quarter-wave plate
(Thorlabs Inc., Newton, NJ). It was found that the light of the
TRIOS scanner was polarized, whereas the light of the
iTero scanner was not polarized. The TRIOS scanner
was found to use linear-to-circular polarization by the
quarter-wave plate. A wave plate is an optical device that
alters the polarization state of a light wave traveling
through it. Two common types of wave plates are the
half-wave plate, which shifts the polarization direction of
linearly polarized light, and the quarter-wave plate,
which converts linearly polarized light into circularly
polarized light and vice versa [
]. In consideration of the
polarization system of the TRIOS scanner, which might
block the scattered reflections, this scanner might have
better optical performance than iTero.
In addition, the iTero and TRIOS systems both
capture single images of each tooth and produce an
assembled virtual model of the whole dentition. This stitching
process might produce systematic errors; however,
because the stitching algorithms of the iTero and TRIOS
scanners are not known, their contribution to such
errors cannot be explained. Intraoral conditions such as
saliva, breathing, movement of the tongue, and limited
oral space can also contribute to scanning inaccuracies.
For example, it is difficult for the scanner tip to access
the lower posterior areas, owing to tongue movement
and limited mouth opening. Flügge et al. [
] found that
intraoral scanning was less precise than extraoral model
scanning, indicating that the intraoral conditions
contribute to the inaccuracy of scans. The accuracy can also
be affected by the examiner’s technical skill at intraoral
scanning. To avoid such bias, in the present study,
intraoral scans were obtained by the same examiner,
who had experienced with over 100 cases of intraoral
scanning. Long scanning times might induce errors in
the stitching process of the captured images; the
scanning times tend to decrease as the operator experience
increased. In this study, the full-arch scan time for the
iTero scanner was an average of 5 min, while the TRIOS
scanner was an average of 4 min. However, further
studies are needed to assess the scanning accuracy according
to the clinician’s experience.
There are few researches about the comparison of
iTero and TRIOS scanner for in vivo and full-arch scan.
For single abutment, the trueness and precision were
higher in TRIOS than iTero scanner [
Renne et al.  reported that trueness and precision for
full-arch scanning was higher in iTero than in TRIOS,
regarding scanning time, TRIOS was found to have the
best balance of speed and accuracy [
]. Although there
were no statistically significant differences between the
two scanners in this study, some deviations might occur
in the posterior areas, particularly in the mandible. In
the clinical setting, the use of a careful and extended
scanning protocol might improve the scanning results.
With the continued development of digital impression
technology, we will likely see the elimination of
conventional impression taking in the near future.
Although there were some deviations in visible
inspection, there was no statistical significance between the
two intraoral scanners.
CAD/CAM: Computer-aided design/computer-aided manufacturing;
The present study was supported by Basic Science Research Program
through the National Research Foundation of Korea (NRF) funded by the
Ministry of Science, ICT and Future Planning (NRF-2014R1A1A1003559). This
research was supported by Basic Science Research Program through the
National Research Foundation of Korea (NRF) funded by the Ministry of
Education (NRF-2017R1D1A1B03032132). All the scanners and materials used
here belonged to the author, and nothing was provided by third-party or
Availability of data and materials
The STL files and the three-dimensional surface models obtained in this
study with the two intraoral scanners belong to the author and are therefore
available only upon request, after approval by the author.
Ethics approval and consent to participate
All participants provided informed consents. The present study was
approved by the Chonnam National University Dental Hospital Institutional
Review Board (CNUDH-2015-003).
Consent for publication
The author declares that there are no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
1. Christensen GJ . Will digital impressions eliminate the current problems with conventional impressions? J Am Dent Assoc . 2008 ; 139 : 761 - 3 .
2. Yuzbasioglu E , Kurt H , Turunc R , Bilir H . Comparison of digital and conventional impression techniques: evaluation of patients' perception, treatment comfort, effectiveness and clinical outcomes . BMC Oral Health . 2014 ; 14 : 10 .
3. Ender A , Mehl A . Full arch scans: conventional versus digital impressions-an in-vitro study . Int J Comput Dent . 2011 ; 14 : 11 - 21 .
4. van der Meer WJ , Andriessen FS , Wismeijer D , Ren Y. Application of intra-oral dental scanners in the digital workflow of implantology . PLoS One . 2012 ; 7 : e43312 .
5. Nayar S , Mahadevan R. A paradigm shift in the concept for making dental impressions . J Pharm Bioallied Sci . 2015 ; 7(suppl 1):s213-5.
6. Duret F , Blouin JL . Optical impressions in the computer-assisted design and fabrication of dental crowns . J Dent Que . 1986 ; 23 : 177 - 80 .
7. Birnbaum NS , Aaronson HB , Stevens C , Cohen B. 3D digital scanners: a high-tech approach to more accurate dental impressions . Inside Dentistry . 2009 ; 5 : 70 - 4 .
8. Kachalia PR , Geissberger MJ . Dentistry a la carte: in-office CAD/CAM technology . J Calif Dent Assoc . 2010 ; 38 : 323 - 30 .
9. Focus on digital oral scanners . Orthodontic products . 2016 : 30 - 1 . http:// www.orthodonticproductsonline.com.
10. Luthardt RG , Loos R , Quaas S. Accuracy of intraoral data acquisition in comparison to the conventional impression . Int J Comput Dent . 2005 ; 8 : 283 - 94 .
11. Syrek A , Reich G , Ranftl D , Klein C , Cerny B , Brodesser J. Clinical evaluation of all-ceramic crowns fabricated from intraoral digital impressions based on the principle of active wavefront sampling . J Dent . 2010 ; 38 : 553 - 9 .
12. Lee SJ , Gallucci GO . Digital vs. conventional implant impressions: efficiency outcomes . Clin Oral Implants Res . 2013 ; 24 : 111 - 5 .
13. Seelbach P , Brueckel C , Wöstmann B . Accuracy of digital and conventional impression techniques and workflow . Clin Oral Investig . 2013 ; 17 : 1759 - 64 .
14. Giménez B , Özcan M , Martínez-Rus F , Pradíes G . Accuracy of a digital impression system based on parallel confocal laser technology for implants with consideration of operator experience and implant angulation and depth . Int J Oral Maxillofac Implants . 2014 ; 29 : 853 - 62 .
15. Giménez B , Özcan M , Martínez-Rus F , Pradíes G . Accuracy of a digital impression system based on active wavefront sampling technology for implants considering operator experience, implant angulation, and depth . Clin Implant Dent Relat Res . 2015 ; 17 ( suppl 1 ): e54 - 64 .
16. Papaspyridakos P , Gallucci GO , Chen CJ , Hanssen S , Naert I , Vandenberghe B . Digital versus conventional implant impressions for edentulous patients: accuracy outcomes . Clin Oral Implants Res . 2016 ; 27 : 465 - 72 .
17. Ender A , Mehl A . Accuracy of complete-arch dental impressions: a new method of measuring trueness and precision . J Prosthet Dent . 2013 ; 109 : 121 - 8 .
18. Patzelt SB , Vonau S , Stampf S , Att W. Assessing the feasibility and accuracy of digitizing edentulous jaws . J Am Dent Assoc . 2013 ; 144 : 914 - 20 .
19. Patzelt SB , Emmanouilidi A , Stampf S , Strub JR , Att W. Accuracy of full-arch scans using intraoral scanners . Clin Oral Investig . 2014 ; 18 : 1687 - 94 .
20. Ender A , Mehl A . In-vitro evaluation of the accuracy of conventional and digital methods of obtaining full-arch dental impressions . Quintessence Int . 2015 ; 46 : 9 - 17 .
21. Kuhr F , Schmidt A , Rehmann P , Wöstmann B. A new method for assessing the accuracy of full arch impressions in patients . J Dent . 2016 ; 55 : 68 - 74 .
22. Anh JW , Park JM , Chun YS , Kim M , Kim M. A comparison of the precision of three-dimensional images acquired by 2 digital intraoral scanners: effects of tooth irregularity and scanning direction . Korean J Orthod . 2016 ; 46 : 3 - 12 .
23. Noh H , Nabha W , Cho JH , Hwang HS . Registration accuracy in the integration of laser-scanned dental images into maxillofacial cone-beam computed tomography images . Am J Orthod Dentofac Orthop . 2011 ; 140 : 585 - 91 .
24. Hirogaki Y , Sohmura T , Satoh H , Takahashi J , Takada K. Complete 3 -D reconstruction of dental cast shape using perceptual grouping . IEEE Trans Med Imaging . 2001 ; 20 : 1093 - 101 .
25. Schirmer UR , Wiltshire WA . Manual and computer-aided space analysis: a comparative study . Am J Orthod Dentofac Orthop . 1997 ; 112 : 676 - 80 .
26. Bell A , Ayoub AF , Siebert P . Assessment of the accuracy of a threedimensional imaging system for archiving dental study models . J Orthod . 2003 ; 30 : 219 - 23 .
27. Vasudavan S , Sullivan SR , Sonis AL . Comparison of intraoral 3D scanning and conventional impressions for fabrication of orthodontic retainers . J Clin Orthod . 2010 ; 44 : 495 - 7 .
28. Koester CJ . A comparison of various optical sectioning methods . In: Pawley JB, editor. Handbook of biological confocal microscopy . 3rd ed. New York: Springer; 2006 . p. 207 - 14 .
29. Babayoff N and Glaser-Inbari I : Method and apparatus for imaging threedimensional structure . US Patent 2007 /0109559; 2007 .
30. Logozzo S , Zanetti EM , Franceschini G , Kilpelä A , Mäkynen A . Recent advances in dental optics-part I: 3D intraoral scanners for restorative dentistry . Opt Laser Eng . 2014 ; 54 : 203 - 21 .
31. Hecht E. Polarization . In: Hecht E, editor. Optics. 4th ed. Harlow: Pearson Education Limited; 2008 . p. 327 - 86 .
32. Flügge TV , Schlager S , Nelson K , Nahles S , Metzger MC . Precision of intraoral digital dental impressions with iTero and extraoral digitization with the iTero and a model scanner . Am J Orthod Dentofac Orthop . 2013 ; 144 : 471 - 8 .
33. Hack GD , Patzelt SBM . Evaluation of the accuracy of six intraoral scanning devices: an in-vitro investigation . ADA professional product review . 2015 ; 10 : 1 - 5 .
34. Imburgia M , Logozzo S , Hauschild U , Veronesi G , Mangano C , Mangano FG . Accuracy of four intraoral scanners in oral implantology: a comparative in vitro study . BMC Oral Health . 2017 ; 17 : 92 .
35. Renne W , Ludlow M , Fryml J , Schurch Z , Mennito A , Kessler R , Lauer A . Evaluation of the accuracy of 7 digital scanners: an in vitro analysis based on 3-dimensional comparisons . J Prosthet Dent . 2017 ; 118 : 36 - 42 .