Virtuelle

1. A Novel Technique to Align the Intraoral Scans to the Virtual
Articulator and Set the Patient-Specific Sagittal Condylar
Inclination
Shengtao Yang, MS ,1
Ning Feng, MS,2
Dan Li, MS,1
Yunshu Wu, DDS,2
Li Yue, BS,1
&
Quan Yuan, DDS, PhD 2
1
Department of Dental Technology, West China Hospital of Stomatology, Sichuan University, Chengdu, PR China
2
Department of Oral Implantology, West China Hospital of Stomatology, Sichuan University, Chengdu, PR China
Keywords
Virtual articulator; sagittal condylar inclination;
intraoral scan; arbitrary hinge axis; reference
plane.
Correspondence
Quan Yuan, Oral Implantology Department,
West China Hospital of Stomatology, Sichuan
University, 14 Renmin South Road, 3rd
section, Chengdu, Sichuan 610041, PR China.
E-mail: yuanquan@scu.edu.cn
Accepted June 22, 2021
doi: 10.1111/jopr.13403
Abstract
Customized cast orientations and parameter settings of the virtual articulator accord-
ing to the patient’s condyles are indispensable parts of today’s digital workflows in
prosthodontics. This article describes a digital technique to align the intraoral scans
to a virtual articulator by using a facial scanner to locate the patient’s cutaneous land-
marks of the arbitrary hinge axis and the reference plane, and to customize the sagittal
condylar inclination of the virtual articulator through a digital protrusive interocclusal
record and a dental computer-aided design software program. It enables individual
cast orientations and virtual articulator parameter settings without conventional face-
bow transferring and bite registration procedures and can be easily integrated with
most virtual articulator systems on the market to allow clinicians and technicians to
work in a complete digital workflow and facilitate customized treatment planning and
dental prosthesis fabrication.
As dental treatments are marching toward a digital era, pre-
cisely reproducing patients’ jaw movements in the virtual
environment by accurately relating the scanned arches to
the virtual articulator and individually setting its parameters
according to the patients’ condyles is critical for making
individualized diagnosis and treatment planning, as well as
achieving good multidisciplinary treatment and restoration
fabrication.1–3
Conventionally, a facebow and bite registration
are used to physically mount the stone casts on a mechanical
articulator, and a protrusive interocclusal record is also needed
to program the articulator; then the mounted casts will be
transferred to the virtual environment by using a laboratory
scanner.4,5
This process cannot avoid the inaccuracies caused
by the deformation of the impression, bite registration, and
stone materials, which make it hard to accurately reposition the
cast into the bite registration without leaving any space, thus
inducing discrepancies.1,6,7
Furthermore, it is time-consuming
as several steps are required.8
In addition, the use of the
impression material and placement of the facebow can easily
cause patient discomfort.9
The introduction of digital impres-
sion techniques can simplify the impression making procedure
by eliminating the need for impression and stone materials
and is more patient-friendly and more accurate compared
to conventional methods.10,11
However, an intraoral scanner
cannot record the spatial relationship between the scanned
arches and the hinge axis of the patient, so an arbitrary mount-
ing is usually conducted and average values of the sagittal
condylar inclination (SCI) are typically utilized, which barely
reproduces patients’ actual jaw movements in the virtual
environment.12
Although some jaw motion tracker devices
can be utilized, their complex nature and prohibitive cost
have limited their widespread implementation in daily clinical
practice.12
Recently, some digital facebow transfer techniques have
been proposed to mount the intraoral scans on a virtual artic-
ulator. These digital methods are based on 3-dimensional (3D)
face models reconstructed by a series of 2-dimensional (2D)
photographs13
or stereophotogrammetry technology14
, and
cone-beam computed tomography (CBCT) data.6
However,
none of them have introduced the acquisition of patient-
specific SCI, which is a crucial setting of the virtual articula-
tor. The method of measuring the SCI by using a mechanical
articulator and a protrusive record was first introduced by
Christensen in 1905.15
Then Seoung-Jin et al proposed a
digital SCI obtaining technique by using intraoral scan and
CBCT scan.3
However, an additional 3D analysis software
program is still needed, which has limited its utilization in the
dental CAD software.
This article aims to propose a digital technique to
align the intraoral scans to a virtual articulator and to
1
Journal of Prosthodontics 0 (2021) 1–6 © 2021 by the American College of Prosthodontists

2. A Technique to Mount Casts and Set SCI Yang et al
Figure 1 Use the transfer fork to obtain a maxillary bite record. A, Transfer fork in position. B, The obtained maxillary bite record.
Figure 2 Digital interocclusal position of the maxillary and mandibular arches. A, Maximal intercuspal position. B, Protrusive intercuspal position.
set the patient-specific SCI by using the patient’s cuta-
neous landmarks and a digital protrusive interocclusal
record through a dental CAD software program to re-
produce individual jaw movements and optimize clinical
workflows.
Technique
1. Load bite registration silicon material (Jet Blue Bite fast;
Coltene, Altstatten, Switzerland) on the upper side of a
specially designed transfer fork (Transfer fork; Zirkon-
zahn, Gias, Italy), and then place the transfer fork in
the patient’s mouth and instruct the patient to lightly
bite down while waiting for the bite registration mate-
rial to be polymerized to obtain a maxillary bite record
(Fig 1).
2. Scan the maxillary and mandibular arches as well as
the maximal intercuspal position (MIP) with an intrao-
ral scanner (iTero; Align Technology, Redwood, Cali-
fornia), then instruct the patient to move the mandibu-
lar arch to an anterior edge-to-edge position and
record the protrusive interocclusal position digitally
(Fig 2).
3. Use a facial scanner (Facehunter; Zirkonzahn, Gias,
Italy) to scan the patient at the rest jaw position, then
scan the patient’s face with the transfer fork in position.
Superimpose the two facial scans by using the forehead
area as merging markers.
4. Scan the transfer fork with a laboratory scanner (S300;
Zirkonzahn, Gias, Italy) and an accessory scan software
program (Zirkonzahn Scan; Zirkonzahn, Gias, Italy).
First, superimpose the scanned arches at MIP with the
scanned transfer fork based on the maxillary bite record,
then use the transfer fork to align the facial scans with
the scanned arches at MIP (Fig 3).
5. Load the merged data above into a dental CAD soft-
ware program (Exocad; exocad GmbH, Darmstadt, Ger-
many). Mark the bilateral Beyron points (13 mm anterior
to the posterior margin of the tragus of the ear on a line
from the center of tragus extending to the outer canthus
of the eye) on the facial scan in the dental CAD soft-
ware. Then use another CAD software program (123D
Design; Autodesk, San Rafael, CA) to create a cylinder
of 2 mm in diameter and 200 mm in length, and load it
back into the first dental CAD software. Adjust its spatial
position to pass through the two located Beyron points
to represent the arbitrary hinge axis of the patient. Add a
reference plane that passes through the left orbitale and
the bilateral porions to generate the Frankfort horizontal
(FH) plane. Adjust the spatial position of the obtained
data, ensuring the arbitrary hinge axis passes through the
2 Journal of Prosthodontics 0 (2021) 1–6 © 2021 by the American College of Prosthodontists

3. Yang et al A Technique to Mount Casts and Set SCI
Figure 3 Superimposition of data. A, Alignment of the scanned transfer fork and the scanned arches at MIP
. B, Superimpose the facial scans with the
intraoral scans through the transfer fork.
Figure 4 Orient the intraoral scans to the virtual articulator. A, Locate the left Beyron point. B, The cylinder passing through the bilateral Beyron point
represents the arbitrary hinge axis of the patient. C, Generate the FH plane by passing through the left orbitale and bilateral portions. D, The arbitrary
hinge axis passes through the centers of the two condylar balls, and the FH plane parallel to the upper arm of the virtual articulator simultaneously.
centers of the two condylar balls and the FH plane is par-
allel to the upper arm of the virtual articulator (Fig 4),
thus achieving an individual intraoral scan mounting.
6. Export the lower arch at MIP with the cylinder as a
single STL file A. Then load the arches at the protrusive
interocclusal position and align them to the arches at
MIP based on the common upper arch to obtain file B.
Load the file A and superimpose it with the file B by
selecting the same three merging markers on the two
mandibular arches. Once the superimposition is com-
pleted, two cylinders that approximately indicate the
starting and ending positions of the arbitrary hinge axis
during the mandibular protrusive movement are located
(Fig 5).
7. Launch the sectional view of the software, and adjust
the position of the sectional plane to pass through the
sagittal center of the right condylar ball of the virtual ar-
ticulator. Then adjust the sagittal inclination of the right
condylar guidance by setting the right SCI of the vir-
tual articulator. Once the condylar guidance control sur-
face is parallel to the line connecting the two centers of
the cross-sectional circles of the two cylinders, the SCI
Journal of Prosthodontics 0 (2021) 1–6 © 2021 by the American College of Prosthodontists 3

4. A Technique to Mount Casts and Set SCI Yang et al
Figure 5 Indicate the starting and ending positions of the arbitrary hinge axis during the mandibular protrusive movement. A, Export the lower arch
at MIP with the cylinder as a single STL file A. B, Align the arches at the protrusive interocclusal position with the oriented arches (at MIP) based on
the upper arch to obtain file B. C, Superimpose file A and file B by selecting the same three merging markers on the mandibular arches from two
separate files. D, The two cylinders approximately indicate the starting and ending positions of the arbitrary hinge axis during the mandibular protrusive
movement.
Figure 6 Set the SCI of the virtual articulator. A, The sectional plane passes through the sagittal center of the right condylar ball of the virtual articulator.
B, Adjust the right SCI until the condylar guidance control surface is parallel to the line connecting the two centers of the cross-sectional circles of the
two located cylinders, and the SCI of the right condyle is measured as 42.5°.
value of the right condyle is obtained, which is measured
as 42.5° by the dental CAD software (Fig 6). Repeat this
step to measure the SCI of the left condyle.
Discussion
Using a combination of a facial scanner, a digital protrusive
interocclusal record, and a dental CAD software program, a
customized intraoral scan mounting is achieved, and patient-
specific SCI is obtained to program the virtual articulator. It
allows clinicians and technicians to simulate jaw movements
in a virtual environment and can be used in treatment planning
and dental prostheses fabrication.
To perform an individual mounting of the intraoral scans, the
spatial relationship between the upper arch and the arbitrary
hinge axis of the patient must be first recorded with a virtual
4 Journal of Prosthodontics 0 (2021) 1–6 © 2021 by the American College of Prosthodontists

5. Yang et al A Technique to Mount Casts and Set SCI
facebow, which necessitates a minimum of two posterior ref-
erence points and one anterior reference point.16,17
Currently,
several posterior reference points that represent the arbitrary
hinge axis have been proposed, such as the Beyron point,
Bergstrom’s point, and Gysi’s point.16
Most of these points
are located by measuring prescribed distances from the skin
surface landmarks.16
In this article, a facial scanner was used
to transfer the facial anatomic landmarks to the virtual envi-
ronment, and the Beyron point was selected, which is accurate
enough to represent the hinge axis and can be easily located in
the dental CAD software.16
The FH plane is the most common
reference plane during the maxillary cast orientation, which
has been assumed to be horizontal when the patient is in the
natural head position.17
It was used in this technique as the
virtual articulator type was Bio-art A7 Plus, which uses the FH
plane as the reference plane, and the upper arm of the virtual
articulator represents this reference plane when the incisal pin
is set at zero.6,16
Although the choice of the reference plane
should be based on the type of the virtual articulator used
in the dental CAD software,6
most of the reference planes
can be easily located on the patient’s facial scan in the dental
CAD software. Therefore, this technique can be effectively
integrated into most of the virtual articulator systems.
To simulate individual jaw movements, patient-specific pa-
rameters must be delivered to program the virtual articulator,
among which SCI is an important value.3,12
This is defined as
the angle formed between the protrusive condylar path and the
FH plane.3
Conventionally, average values of the SCI are uti-
lized when an intraoral scanner is employed. Seoung-Jin et al
proposed a digital SCI obtaining technique by using the pro-
trusive interocclusal position and a CBCT scan, however, an
extra 3D analysis software program is needed, which limits its
application in the dental CAD software.3
Although several jaw
motion tracker devices are now available to accurately record
individual mandibular movement paths, their complex clini-
cal procedures and prohibitive cost must also be taken into
consideration.12
This article describes a customized SCI ob-
taining technique by using a digital protrusive interocclusal
record and a commonly used dental CAD software program.
Theoretically, it is analogous to the conventional SCI acquisi-
tion method proposed by Christensen. However, analogue ar-
ticulator mounting and protrusive recording procedures are re-
placed by digital methods, which are relatively simple. Once
the intraoral scans are oriented and the virtual articulator is
programmed, subsequent treatments planning and dental pros-
theses designing can be directly conducted in the same dental
CAD software.
The limitation of this technique is the need for a 3D facial
scanner, so it may be more applicable to cases that initially
need the 3D facial data to perform smile design or other treat-
ment plans. In this article, a prefabricated transfer fork was
used, however, it can be easily replaced by plastic impression
trays.14
In addition, various digital data sets are integrated dur-
ing the scan mounting and SCI obtaining procedures, so addi-
tional attention must be paid in selecting the alignment points;
a verification process such as using the cross-section view is
also needed to reduce superimposition inaccuracies. Mandibu-
lar movements are highly individualized, and compared to jaw
motion tracker devices which record the exact movement paths
of the mandible, the virtual articulator is limited in its ability
to simulate the variability of biologic systems.7
In this article,
mandibular movements reproduced by the virtual articulator
through parameter setting are somehow still arbitrary. In addi-
tion, several software programs and devices are introduced in
this technique, which require some additional cost, chairside
time, and software operating knowledge. Besides the SCI, lat-
eral condylar inclination is also an essential parameter. Meth-
ods for measuring the lateral condylar inclination are needed in
further studies. Studies are also expected to compare this tech-
nique with conventional methods to evaluate its precision and
efficiency.
Summary
The present article describes a complete digital workflow to
individually align intraoral scans to a virtual articulator and set
customized SCI without conventional facebow transferring and
bite registration procedures to optimize clinical workflows.
Acknowledgment
We would like to thank Linxin Liu for his assistance in facial
scan and intraoral scan procedures.
Funding
This work was financially supported by National Natural Sci-
ence Foundation of China (grant number: 81722014).
Declarations of interest
The authors declare that there are no conflicts of interest in this
study.
References
1. Koralakunte PR, Aljanakh M: The role of virtual articulator in
prosthetic and restorative dentistry. J Clin Diagn Res
2014;8:25-28
2. Solaberrieta E, Mínguez R, Barrenetxea L, et al: Direct transfer
of the position of digitized casts to a virtual articulator. J
Prosthet Dent 2013;109:411-414
3. Hong SJ, Choi Y, Park M, et al: Setting the sagittal condylar
inclination on a virtual articulator using intraoral scan of
protrusive interocclusal position and cone beam computed
tomography. J Prosthodont 2020;29:185-189
4. Farias-Neto A, Dias AH, de Miranda BF, et al: Face-bow
transfer in prosthodontics: a systematic review of the literature. J
Oral Rehabil 2013;40:686-692
5. Gärtner C, Kordass B: The virtual articulator: development and
evaluation. Int J Comput Dent 2003;6:11-24
6. Lepidi L, Chen Z, Ravida A, et al: A full-digital technique to
mount a maxillary arch scan on a virtual articulator. J
Prosthodont 2019;28:335-338
7. Kordass B, Gärtner C, Söhnel A, et al: The virtual articulator in
dentistry: concept and development. Dent Clin North Am
2002;46:493-506
8. Kim JE, Park JH, Moon HS, et al: Complete assessment of
occlusal dynamics and establishment of a digital workflow by
using target tracking with a three-dimensional facial scanner. J
Prosthodont Res 2019;63:120-124
Journal of Prosthodontics 0 (2021) 1–6 © 2021 by the American College of Prosthodontists 5

6. A Technique to Mount Casts and Set SCI Yang et al
9. Farias-Neto A, Dias A, de Miranda B, et al: Face-bow transfer in
prosthodontics: a systematic review of the literature. J Oral
Rehabil 2013;40:686-692
10. Wong KY, Esguerra RJ, Chia VAP, et al: Three-dimensional
accuracy of digital static interocclusal registration by three
intraoral scanner systems. J Prosthodont 2018;27:120-
128
11. Sakornwimon N, Leevailoj C: Clinical marginal fit of zirconia
crowns and patients’ preferences for impression techniques
using intraoral digital scanner versus polyvinyl siloxane
material. J Prosthet Dent 2017;118:386-391
12. Lepidi L, Galli M, Mastrangelo F, et al: Virtual articulators and
virtual mounting procedures: where do we stand? J Prosthodont
2021;30:24-35
13. Solaberrieta E, Garmendia A, Minguez R, et al: Virtual facebow
technique. J Prosthet Dent 2015;114:751-755
14. Lam WYH, Hsung RTC, Choi WWS, et al: A clinical technique
for virtual articulator mounting with natural head position by
using calibrated stereophotogrammetry. J Prosthet Dent
2018;119:902-908
15. Christensen C: The problem of the bite. Dent Cosmos
1905;47:1184-1195
16. Raghav D, Kapoor K, Alquahtani A, et al: Intricate relations and
concepts of reference points in prosthodontics: a literature
review. Eur J Prosthodont 2016;4:1-6
17. Ercoli C, Graser GN, Tallents RH, et al: Face-bow record
without a third point of reference: theoretical considerations and
an alternative technique. J Prosthet Dent 1999;82:
237-241
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