Lab Tribune Middle East & Africa No.4, 2023
Researchers use generative artifificial intelligence to design realistic dental crowns / Digital workflow for 3D-printed complete dentures
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DTMEA_No.4. Vol.13_LT.indd
PUBLISHED IN DUBAI
www.dental-tribune.me
Vol. 13, No. 4
Researchers use generative
artificial intelligence to design
realistic dental crowns
By Iveta Ramonaite, Dental
Tribune International
CAD/CAM technology has
greatly improved the productivity
of dental prostheses but still has its
drawbacks when it comes to the
design of crowns. Using an artificial intelligence (AI) learning
method, researchers from the
Faculty of Dentistry at the University of Hong Kong have created an
algorithm for personalised dental
crown design of high accuracy to
produce crowns that resemble the
morphology and biomechanics of
natural teeth.
According to the researchers,
the CAD/CAM workflow has significantly improved dentistry, but is
still labour-intensive and timeconsuming, particularly because of
the need for customisation for each
patient, despite CAD software
using a tooth library to assist in
generating prosthetic designs, and
it generates health and environ-
Fig. 1: Project co-investigator Dr Hao Ding and the design of a tooth crown using generative AI.
Fig. 2: Researchers make use of generative AI to design personalised dental
crowns.
mental
hazards
during
the
3D-printing and milling processes.
CAD/CAM remakes are often necessary because of marginal misfits,
and design can affect the biomechanical performance and thus the
fatigue lifetime of the crown. For
this reason, a means of crown design that addresses these issues is
needed.
In the study, the researchers
trained the algorithm on 600 sets
of digital casts of mandibular second premolars and their adjacent
and antagonist teeth and tested it
on an additional 12 sets of data to
generate 12 crowns. They then
Fig. 3: Natural tooth (left) compared with tooth tailored by generative AI (right).
Fig. 4: The HKU Dental Materials Science research team: (from left) co-investigator
postdoctoral fellow Dr Hao Ding, principal investigator Dr James Kit Hon Tsoi, and
PhD candidate Ms Yanning Chen.
compared the natural second premolars with the designs created by
their algorithm, using CEREC software and by a technician using a
CAD program. They looked at morphological parameters of 3D similarity, cusp angle, and number and
area of occlusal contact points.
They also subjected the designs realised on computer in lithium disilicate to biomechanical fatigue simulations based on physiological occlusal force.
“During the training process,
natural teeth morphological features were learned by the algorithm, so that it can design dental
crowns comparable to a natural
tooth—both morphologically and
functionally,” lead author Dr Hao
Ding, a postdoctoral fellow in applied oral sciences and community
dental care at the university, said in
a press release.
The generative AI-designed
crowns had the lowest 3D discrepancy, closest cusp angle and similar
occlusal contacts compared with
natural teeth. In lithium silicate, the
AI-designed crowns were found to
have an expected lifespan similar to
that of natural teeth. According to
the researchers, the other two
methods of designing dental
crowns produced crowns that were
either too large or too thin and
failed to reach the same lifespan as
that of natural teeth.
“This demonstrates that [the algorithm] could be utilised to design personalised dental crowns
with high accuracy that can not
only mimic both the morphology
and biomechanics of natural teeth,
but also operate without any additional human fine-tuning, thus saving additional costs in the production process,” added senior researcher Dr James Tsoi, an associate professor in dental materials
science at the university.
“Many AI approaches design a
‘lookalike’ product, but I believe
this is the first project that functionalises data-driven AI into real
dental application. We hope this
smart manufacturing technology
will be the stepping stone for driving Industry 4.0 in dentistry, which
is vital to meet the challenges of an
ageing society and lack of dental
personnel in Hong Kong,” Dr Tsoi
stated.
Clinical trials for using the generative AI for dental crowns are underway. Additionally, the researchers are working to expand the applicability of the tool to other dental prostheses, such as partial and
complete dentures.
Editorial Note: This article was published
in digital international magazine of
digital dentistry vol. 4, issue 2/2023.
[2] =>
DTMEA_No.4. Vol.13_LT.indd
LAB TRIBUNE
B2
Lab Tribune Middle East & Africa Edition | 04/2023
Digital workflow
for 3D-printed complete dentures
1
By Dr Fernando Gérman, Spain
Digital dental workflows are no
longer a promise of the future, but
the reality we live in today. The entire work protocol from diagnosis
to treatment has digital elements,
even though there are still gaps
when it comes to the complete digitalisation of the dental office.
Do you consider yourself a digitised professional because you
have an intra-oral scanner? That is
only a small but very significant
part of the framework, especially
when it comes to a full digital workflow for a complete or partial denture.
2
the medium to long term will allow
us optimal results.
Steps for a complete scan of
an edentulous patient
1) We start with a complete
scan of the upper jaw from the retromolar area to the palate and palatal rugae. It is important to have
some particular anatomy that differentiates one side from the other
so that the software does not confuse the scanned sides and
cross-reference the information.
The tissue of the vestibular part
3
must be retracted and separated
for better fit of the future printed
prosthesis. Although it is complex,
it is essential, and in fact there are
techniques that result in a betterquality scan to achieve this peripheral sealing.
2) We then continue with the
scanning of the lower jaw, from the
posterior region, as well as the
upper jaw, passing along the plateau or gingiva-covered alveolar
ridge to the opposite side. It is important to be able to obtain a good
extension of the lower jaw in the
software (Medit), which provides us
with a suitable structure for classic
models with a base and articulators. Afterwards, it can be sent to
the SprintRay printer in two different ways, depending on the user’s
preferences and experience:
1) Sending to RayWare Cloud:
Printing of the lower and upper jaw
models is a user-friendly process
thanks to an artificial intelligence
(AI) program which arranges the
same way as in the upper jaw so
that the denture can be fully extended for a better fit.
3) Next, we obtain a bite registration to establish the relationship between the upper and lower
jaws, whether dentate or edentulous.
Starting the 3D-printing process
At this point, after taking scans
of both arches, we send the STL file
to and transform it into a printable
model using the Model Builder
▶ Page B3
Phases of the CAD/CAM process in digital dentistry and 3D
dental prostheses
Methodology
The methodology used for
CAD/CAM involves optical scanning of the jaw without the need for
alginate and employing those
scans in design software to design
and 3D-print dental appliances
with maximum accuracy.
By using the digital STL file
from the design process, we can realise the denture or bridge we see
on screen. To do this, we need a
high-speed scanner (Fig. 1) for
complete marginal definition of
soft and hard tissue. We use the
Medit i700. The same efficiency is
also provided by the Medit i500.
We also need an adequate bite registration that allows us to determine the vertical dimension and
correct intermaxillary relation for
the positioning of the prosthesis,
whether complete or partial, based
on the centric relation and the peripheral tissue (mucosa and lips).
We need an automatic means of
sending all the scan data to the associated laboratory or a design
program to interpret the scanned
data and design the prosthesis ourselves. Finally, once the prosthesis
has been printed, we must follow a
protocol that guarantees a material
with the required characteristics of
resistance, polishing and final finishing for better adaptation and
dura- bility in the patient’s mouth.
Naturally, the digital method also
requires time and training that in
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[3] =>
DTMEA_No.4. Vol.13_LT.indd
LAB TRIBUNE
B3
Lab Tribune Middle East & Africa Edition | 04/2023
◀ Page B2
13
designs in the best way possible
automatically on the build platform
for fast and optimal printing. In this
case, the scan files must be saved
on the PC and uploaded to the
SprintRay Cloud program.
2) Using RayWare Desktop:
From the same Medit app, the scan
files are uploaded to the printing
program directly. In this case, the
user must arrange the designs on
the build platform for good retention and print quality. This program
provides the possibility of adding
supports and deciding on the print
position, based on the user’s training.
Obtaining the jaw models
With both methods, we will
have the scanned jaws ready for the
fabrication of the bite registration
to record the intermaxillary relations. Having models of the jaws
enables creation of a base plate for
AD
14
a classic occlusal rim (Fig. 2) that
provides:
– the bite registration;
– the occlusal dimension;
– the relationship between the
jaws; and
– the future size of the teeth
and prosthesis in relation to the patient’s lips (facial profile).
Once we have both jaw models
printed and the base plate with adequate wax registration, we mark
reference points on the wax that we
are going to scan with a marker or
coloured composite (Fig. 3) and
scan both registrations in the bite
sequence.
Once we have obtained all this
data according to the scanning
techniques of the sequence protocol guided by the Medit program,
we will be able to send it to the laboratory for final design.
Viewing the prosthetic design and understanding the STL
files
Our laboratory designs the
prosthesis digitally, and we receive the prosthetic design for our
inspection and control. The design
can be viewed on a mobile device
(Fig. 4) or on our computer to check
and make any necessary changes.
Once we have received these
images and approved the design,
we receive an STL file that can be
sent to the SprintRay printing system to print via RayWare Cloud or
via RayWare Desktop.
Once we receive the final STL
file, we download it to our computer. The file contains the design
of the dental pieces that can be
grouped in a single block (Fig. 5) or
separated by segments. These
pieces will be the ones that we will
cement to the printed denture
base. The file also contains the design of the denture base with de-
tailed anatomy, as traditionally
done in wax denture design systems. In this case, the details will be
digitised, imitating the gingiva and
roots. Later, we will be able to provide more detail with stains and colours that mimic the gingiva in a
more natural way (Fig. 6).
motor, high-precision propeller
and innovative alcohol delivery
method, this system can complete
a full two-stage wash and dry cycle
in less than 9 minutes, meaning
that the dentist or assistant does
not need to be manually involved
in the process.
Printing the prosthesis
The STL file that we have on our
computer is sent to RayWare Cloud
for adaptation and placement,
through an AI process, on the virtual platform that appears on the
program’s screen (Fig. 7).
We must classify the parameters (Fig. 8) for printing and follow
the intuitive steps that the program
prompts, such as:
1) the name of the patient or
the print job;
2) the type of material that will
be used for the printing of the base
or the teeth;
3) the quality of the surface finish, smoother for structures with a
more detailed finish and less detailed for a faster print;
4) the type of support that will
fix the structure to the platform;
and
5) other details that we can customise or leave as the program default.
When the printing process is
started, the time that it will take is
shown, as is the amount of resin to
be used and other data that will
later be saved in the RayWare
Cloud file.
For the manufacturing of the
dental pieces, SprintRay offers material that has similar wear and tear
properties to those of a natural
tooth. The material is called Sprint
-Ray Crown (Fig. 9). For the base of
the prosthesis, there are different
colour options that provide a similar chroma depending on the gingival colour we choose.
Post-processing: Polymerising in ProCure 2
The pieces must be polymerised with an ultraviolet light that
closes micropores and gives the
prosthesis the texture and uniformity necessary to obtain a surface
of adequate rigidity and/or flexibility according to the characteristics
of the material used. That is where
ProCure 2 (Fig. 12) fits into the digital workflow, offering an easy and
automated program requiring less
than 5 minutes with preset profiles
for each approved material. With
ProCure 2, no manual manipulation
of light intensity or duration of the
polymerising process or heat is
necessary.
After printing
When the printing is finished,
the platform will be lifted out of the
resin tank and the piece will be finished. We will only have to remove
the supports that held the prothesis to the print platform (Fig. 10).
If RayWare Cloud was used, the
supports will be a mesh or net that
can be removed easily by hand,
greatly improving the process of
finishing the prosthesis, unlike
other systems that require support
removal with pliers and cutters because they are very thick and leave
a residue on the prosthetic structures, requiring polishing. That is
why we use RayWare Cloud, as it
provides us with supports that are
very easy to remove without leaving any residue.
Post-processing:
Washing
and drying
The liquid resin that remains on
the printed pieces must be washed
off thoroughly. For this, SprintRay
has an automatic washing and drying system that ensures that the
printed piece is free of resin residue, ready for polymerisation and
finishing. SprintRay Pro Wash/Dry
(Fig. 11) is the first multistage automated wash and dry system designed for dental 3D printing, offering the speed, cleanliness and ease
of use that the digital workflow demands. Thanks to its high-powered
Assembly and finishing of
the prosthesis
Now we assemble both the
base of the prosthesis and the
teeth in order to use the same resin
that we have in the tray to cement
the two together. The constructed
piece is then placed in ProCure 2
for final fixation.
Subsequently, we polish the
final product using classic polishing
pastes and various polishing
brushes, finishing with the fabric
brush that gives it a special final
shine (Figs. 13 & 14). The work can
be finished by glazing it with a GC
glaze and polymerising it again in
ProCure 2 or with a common composite polymerising lamp that
gives a brighter finish. It should be
noted that there are different stains
or flowable composites that can be
used to further customise the prosthetic finish.
Conclusion
Although the digital workflow
of 3D-printing complete prostheses may seem complex and lengthy
at first, process automation with
the latest technology means that
dental clinics that embark on this
new and wonderful adventure have
only benefits to look forward to in
the long run.
Editorial Note: This article was published
in digital international magazine of
digital dentistry vol. 4, issue 1/2023.
Dr Fernando
Gérman
completed
postgraduate studies in implantology
at New York University in the US.
He is director of the Dentinova dental
practice in Barcelona in Spain and of
Dentinova Academy (www.dentinova.
es). He is a key opinion leader for SprintRay Iberica, a speaker for ETK Implant
and a Medit instructor at Dentinova
Academy.
[4] =>
DTMEA_No.4. Vol.13_LT.indd
Dental
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/ Digital workflow for 3D-printed complete dentures
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