Article Type : Review Article
Authors : Jef M van der Zel
Keywords : CAD/CAM; Digital dentistry; Intra-oral scanner; Additive manufacturing; Virtual patient; Scaffold; Telecare; Dental materials; Chairside; Ceramics
The first steps towards the digitization of dentistry
were published more than 46 years ago by the French dentist François Duret in
1973, in his thesis entitled "Empreinte optique" [1]. In 1985 he produced
the first acrylic crown with CAD/CAM at the congress of the ADF (Association
Dentaire Française) [2]. In the 1980s, several people began to take an interest
in the subject, notably Matts Anderson, in Sweden, Werner Mörmann in
Switzerland, Jef van der Zel in the Netherlands, Dianne Rekow, in the United
States and Sadami Tsutsumi in Japan [3] . This new period was a period of
scientific and technical struggle between the pioneers, but also a time when
all early actors were discovered, brought together and appreciated. The
friendship of the united actors with Duret [1], Mörmann and Brandestini (CERECTM)
[4], Rekow [7], Van der Zel (CICEROTM) [5], Anderson (PROCERATM)
[8], Tsutsumi and Fushita [6] has never been denied. The systems that were
commercialized originated in existing companies, producing such as dental
equipment, dental materials or implants. Due to a lack of venture capital, some
systems got stuck in the prototype stage. The earliest people shared that they
had been fascinated from the start by the possibilities of the computer for
automating the dental restorative process. The many mutual contacts in the
early years resulted in an exchange of ideas, which can be regarded as a
healthy curiosity. In the 1990s we see for the first time the emergence of many
other systems, then the emergence of outsourced machining centers and finally
market dominance by large groups (Siemens, NobelBiocare, Bego, Kavo, Girrbach,
etc.). It should be noted here that it are European companies that dominated
the market. Then came the 2000s, with the rise of open systems and the
worldwide use of zirconia. During this period, more and more systems came onto
the market and the market continued to grow.
In the beginning it was absolutely uncertain whether
digital technologies would improve the quality and possibilities in research,
diagnosis and treatment of the dental patient compared to conventional methods.
It is also questionable whether such digital methods provide sufficient
accuracy in data collection and assessment, improve efficiency in treatment
planning, and improve treatment efficiency. The new developments in 3D
engineering in comprehensive dentofacial rehabilitation will have to prove new
possibilities and benefits in using a digital approach [3]. We are now seeing
how the three components of digital dentistry: digitization, design and
production have further converged into standard applications.
The first commercially available CAD/CAM system was
CERECTM, which enabled delivery of inlays and onlays in one visit
[4]. Central manufacturing centers for the supply of alumina copings, PROCERA™
and for veneered two-layer crowns, CICERO™ were introduced at approximately the
same time [8,5]. Together, these systems have catalyzed the evolution of new
materials as well as the development of CAD/CAM and multiple new materials [9].
The first forms of digital imaging included both an intraoral imaging system
integral with the CERECTM system, and a triangulation laboratory
scanner integral with the CICEROTM system and evolutions in digital
radiography. First introduced in the late 1980s, digital radiography has
transformed the field and improved image quality, moving from phosphor plates
to solid-state detectors, cone beam computed tomography (CBCT), and new
generations of intraoral scanners. CBCT is a relatively young X-ray imaging
technique within dentistry. The quality of the image reconstructions has
improved significantly since its introduction. As a result, the application
possibilities have also increased. Much attention is currently being paid to
the diagnostic value of CBCT for various dental diagnostic questions [10].
Three-dimensional visualization makes it possible to view the depicted object
from different sides and to perceive it as a “virtual reality” object.
Dentistry is changing with the imposition of digital systems that make almost
everything in dentistry possible. Today's digital systems are user and patient
friendly, and versatile. Pioneering efforts of the early systems could only
fabricate inlays and onlays or copings or single crowns. Now there seems to be
no more limitation in the types of restorations that can be produced, ranging
from simple inlays to digitally designed and manufactured complete dentures,
orthodontic appliances, study models, implant related components and both
simple and complex surgical guides [11]. Introducing open architecture has
redefined how and where data flows from design to fabrication, creating new
networks [12].
When the World Wide Web was invented in 1989, now,
just 30 years later, the transformation to artificial intelligence and
advancements in neural networks is underway [13]. Over the centuries, dentistry
has survived and thrived despite all these changes. Care and longevity of the teeth
and oral facial complex has been improved. Digital dentistry has changed the
way dentists think and function. It has improved the patient experience and
created a distributed workflow that can benefit from outsourcing various
functions.
In 2020, the majority of European restorations are
outsourced in Asia. Large design studios in China are active in designing
restorations overnight. Other digital applications and innovations are
impacting dentistry technology-assisted health monitoring and care, telecare,
artificial intelligence and innovation in student education. These changes are
likely to have a greater impact on the future of dentistry than we currently
realize.
Telecare data from smart digital health devices can be exchanged between
clinicians/healthcare providers. It is therefore not surprising that telecare
is growing rapidly. Telecare enables patient care and remote communication both
with patients and for consultation with other professionals and brings telecare
to disadvantaged areas and to people who have difficulty traveling to
healthcare facilities. With telecare, point-of-care options and diagnosis are
further expanded. Other mobile systems integrate communication software with
real-time active entry of clinical patient data. In dentistry, telecare is used
for many conditions/ situations. Patients and clinicians both find benefits in
telecare.
The digital patient card will be an important step
towards an actual reversal of care chain. This may include information about
the medical and dental treatments that have been performed and a dental health
documented with X-rays. With this information in his pocket, the patient will
more easily consult the information network with his care needs. A digital
patient card offers benefits to all involved. Island solutions in dental care
will run out. Instead, administration, image processing and equipment will
increasingly be integrated into a common practice system. Until now,
overarching coordination of data and images has been prevented by systems. The
development of an open communication standard and a digital patient card
prevent duplication of data entry and the resulting errors. Due to the
transition to digital archiving, the care process (all activities related to
research and treatment of patients) will become increasingly dependent on ICT.
Reliability, availability and continuity are paramount. The data that must
always be available for the care process require solid and safe storage
facilities.
Dentistry is becoming multi-track. The importance of
special and new treatment methods will increase, and more and more practices
will specialize. To this end, the need to provide information to critical
patients is growing. A dental practice without visualizing patient information
will therefore be clearly out of place. Dental laboratories will have to
fundamentally adapt on a number of different fronts. They too will have to
indicate what their well-developed and less well-developed qualities are.
Laboratory owners who refuse to do so and want to maintain their entire
traditional value chain in an integrated manner - either horizontally or
vertically - are lost. They will be attacked via the networks not only on their
core competence, but on several fronts simultaneously. Computer-aided
outsourcing, especially to Asia, will increasingly play a role in the
production of dental restorations. The cost savings it achieves now will only
increase in the near future. Making optimum use of information networks means
that it is possible to decide at any conceivable time which business process is
the best for which provider at what time and at which price-quality ratio. In
short: utilizing the information networks for its own competitive advantage.
Computer-aided outsourcing is only possible if dental laboratories dare to
share information about product systems, business processes and logistics with
their business partners. Do I dare, can I, do I want that? In a nutshell, this
is the dilemma that laboratory owners face today [3]. Without the existence of
the global information networks, the countries of the second and third world
would have a reasonable chance to independently develop into regional powers of
interest, albeit mainly as a follower and (cheap) supplier.
At present scanners, both intraoral and laboratory
based, have informed restorative dentistry [3]. Real-time imaging proves
digital on-screen images of one or more teeth, whole arches, opposition arches,
occlusion and surrounding soft tissue. With on-screen images explaining
treatment options for patients is simplified. Patients appreciate the more
comfortable data collection process. Space-saving plaster models are replaced
by easy-to-archive digital files. Data can be played at any time for various
reasons.
It is now possible to scan one complete dental arch
within minutes, without the need for a tooth coating. The recording in color is
possible in half, but does not achieve the accuracy of a color spectrometer
[12]. Scanners are on carts, are portable (in the hand/tablet) or are
integrated in the dental chair. Most are wireless. Whereas the intraoral
scanners used to be closed, most are now open communication with the different
design stations.
Accuracy and correctness between scanned data and
reference data have been extensively studied. Results even with design only
scanners show slight differences between intraoral scanned data, extraoral scan
data and conventional impression/model data, although all are inside acceptable
limits for clinical use [13-17].
Obviously, sharp angles, powder coating and long
dental arch spans can affect accuracy [34]. The scan pattern can affect
accuracy [35] or not [36], depending on the case and which scanners were used.
However, the major concern is whether or not the restorations produced from
intraoral scan data have an equal quality as those produced by conventional
impressions. Most studies show that there is no difference in the fit of the
produced restorations by these two data acquisition approaches [18,19].
Digitally fabricated 3-piece ceramic substructures have a better fit than
conventionally fabricated metal substructures [20].
For the digitization to be successful it must
drastically improve the user-friendliness, efficiency and cost-effectiveness of
dental care. The development of a multifunctional intra-oral dental scanner,
which can scan the color of the tooth as well as the geometry of the
preparation and its environment, directly in the mouth of the patient in the
dental chair. It is one of the strategically most important goals of
computer-aided dentistry because it represents the starting point for a
computer-aided production of dental restorations - either chairside or by a
central manufacturing center. This means that the patient can be provided with
ceramic restorations quickly and comfortably, and sometimes in one appointment.
The latter can easily compete with the handmade equivalents with the latest
production technology in aesthetics. The intra-oral scanner puts the dentist in
a position where he is able to access the internet and 'obtain' the most
favorable price-quality restoration for his patient.
Since the first triangulation scanner was shown at the IDS in 1992 [4],
at least 20 laboratory scanners are now available, suitable for scanning
plaster models or impressions. All of them have an accuracy of at least 15µm
and are widely used in the office laboratory workflow [21-23].
Integration of data from multiple sources along with
improved user interface and CAD software capabilities opened important options.
Software modules now include robust aesthetic enhancements including “smile”
design, tooth shape libraries, color matching and denture placement. Other
enrichments integrate tacking the jaw to improve and automate components of
dynamic occlusion [11].
Digital smile design integrates digital photos from facial and software
analysis to help practitioners and laboratory technicians create and plan a
course for treatment, a virtual simulation of the final aesthetic result. This
is especially valuable in complex, multidisciplinary restorations. It enables
and facilitates communication between clinicians and the laboratory.
Importantly, it is also critical in pre-treatment discussions with patients,
involving them in choices that affect aesthetics and creating realistic
expectations the patient has for treatment outcomes. Tooth and dentin shape
libraries provide a common, smooth initial shape and proportions, making
restoration design nearly automated and greatly accelerated [22-24].
Occlusion is a critical factor in restorative and
antagonist design and longevity and patient satisfaction. Jaw dynamics captured
by conebeam computed tomography (CBCT) or a scanner creates a virtual
articulator. The full range of static and dynamic jaw movements and occlusion
are recorded and can be integrated with smile design, computer-aided
implantation planning and digital oral surgery planning. Unfortunately,
integrating data from multiple sources is not yet completely seamless,
requiring interactive transfer of files between systems and user interactions
for superpositions [27,28].
Integration of functional occlusion using virtual
articulation in CAD-CAM complete dental prosthetic rehabilitation is
implemented in some CAD software [29].
The emergence of high hardness monolithic zirconia restorations requires
a test for dynamic fault contacts, before milling, given the difficulty in
occlusal adjustments in the dental chair. Therefore, an exact digital record of
static and dynamic maxillary-mandibular relationships is necessary. The CICEROTM
articulation software detects disturbances occurring near the bucco-lingual
transverse edge, which are not easily detected at the chair, but are easily
incorporated into the design of the occlusal plane [29,30].
While the functional components of data acquisition,
design, and manufacturing have not changed with modern CAD/CAM systems, the
choices in how work flows through the process have changed dramatically [3].
Open architecture of digital systems created new opportunities. Instead of
closed systems in which all functional components are incorporated in a CAD/CAM
system, now functional components from different manufacturers can be selected
and linked by the user. This allows the processes for making restorations to be
made to be distributed in order to best suit the interest, capabilities, and
skills of those who contribute to the fabrication of dental components [31,32].
The integration of data from multiple digital
technologies, including the new 5G network, extends the scope of what is
possible. The digital patient data is vital in computer-aided surgery/dynamic surgical
navigation, robots performing dental procedures, CAD/CAM, and new approaches to
restorations and tissue one-appointment technical scaffolds. Integration of
facial data creates the digital patient from photographs or various 3D tracking
devices, radiographic information, intraoral image data, as well as other
digital data that may be appropriate (e.g., CBCT scans, etc.). Using the
virtual patient as a platform, it enables development of a digital treatment
plan, on-screen design and simulation of procedures such as design of
restorations, surgical navigation for implant placement or craniofacial (and
other) operations, and virtual models for teaching and communication with a .
Creating the virtual patient reduces the number of errors that can be
introduced using conventional approaches, shortens planning time and increases
patient intuitiveness [33-35].
Additive manufacturing, also called 3D printing, is
now a fully integrated option in CAM hardware, offering an alternative to
subtractive machining (milling). The most unique factor in additive
manufacturing is the flexibility of the design. A solid block no longer has to
be the starting point for manufacturing. Instead, products are built layer by
layer, allowing for a high degree of geometric complexity. Now that products
can be produced with different internal geometries as well as the desired
topographic geometry, it is not yet clear how this innovation in dental
prosthesis design is capitalized in this case.
Several 3D printing technologies are available, of
which stereolithography (SLA) is the most widely used [36] Invisalign was one
of the first to use 3D printed models with sequential tooth positions for which
orthodontic aligners have been manufactured. Today, 3D printing can produce an
exceptionally wide range of dental “components”, including everything from
simple models, wax molds, tooth-colored temporary restorations and surgical
molds, to more complex metal and ceramic restorations and digitally fabricated
full dentures. Depending on the system, material choices include glass ceramic,
cobalt chrome, composites, PMMA, resin/polymers, wax, titanium, zirconia, with
more and more choices becoming available with new material innovations.
The quality of 3D printed products is at least
equivalent to that produced by more conventional methods [37,38]. Specific
studies indicate that 3D printing of temporary crowns has a better fit [39],
that drilling templates are accurate to 0.25o from planned implants
[40], that occlusal splints have a similar polished surface and wear.
Correctness of exterior surface, occlusion surface, marginal area and occlusal
surface of 3D zirconia printed crowns was no worse than the corresponding
milled crowns [41]. Custom templates and craniofacial prostheses provide good
aesthetics and a better fit than traditional methods.
3DP plays an essential role in diagnostics and
treatment planning and in improving patient communication, skills training and
oral surgery [42]. Cheap printers can be a realistic alternative to in-house
production. It can produce clinically acceptable temporary crown and bridge
restorations [43], full arch models and digital copies of orthodontic plaster
models. This allows the creation of realistic models with sufficient
dimensional integrity for various applications.
What 3D printing adds to digital dentistry is that it enables material
innovations [36]. Computer aided design and fabrication (CAD/CAM) of complete
dentures is showing exponential growth in the dental market with the number of
commercially available CAD/CAM prosthesis systems just growing. There is
evidence to document improved physical properties of the CAD/CAM dentures as
compared to conventionally manufactured ones; one of these features is
adjustment of the prosthesis and an improved fit of the upper jaw. With CAD/CAM
dentures they can be fabricated with slight compressibility of the tissue or no
compressibility at all in the posterior sealed area.
The intraoral scanning devices have become more
accurate and popular, so the intraoral scan, the so-called “digital impression”
of implants is widely used. For the intra-oral scan of implants, there are many
different ways to do this. Scannable attachments already included in the CAD/CAM
software library can be easily recognized.
On the basis of advanced technological developments,
it is expected that computed tomography will gain in significance in dentistry.
The development of X-ray detector arrays is currently enabling the recording of
a full projection surface. This principle is already used in Cone Beam CT
scanners. With this so-called CBCT technique, specific solutions for dentistry
can be built at a reasonable price, with which an accurate three-dimensional
image of the jaws and the mid-facial area can be made with a very low radiation
load. This creates the possibility of using CT scanning more widely in the
future in design and planning in restorative and prosthetic dentistry.
Data obtained by computed tomography (CBCT) and other digital imaging
techniques combined with 3D printing have significantly influenced tissue
engineering [44,45]. Transforming craniofacial reconstruction over the last two
decades, this integration has opened new possibilities for complex craniofacial
reconstruction through personalized scaffold constructions based on patient
specific anatomical data [45]. The biocompatibility, printability and
mechanical properties of extrusion-based bio-ink printed scaffolds are well
documented [46]. The impact of digital dentistry on scaffolds and tissue
engineering cannot be overlooked. It is undoubtedly a ripe area for materials
science research.
One of the achievements of computer-aided
dentistry is that it has enabled the use of high-strength zirconia ceramics.
The introduction of this material in restorative and prosthetic dentistry will most
likely be the decisive step towards metal-free all-ceramic without restrictions
[3]. The recent evolution in CAD / CAM technologies is breathtaking, enabling
clinicians and dental technicians to fabricate indirect restorations in the
laboratory or at the chair in the dental office from a variety of ceramic
materials, from resin matrix ceramics to silica-based and highly strong
ceramics such as lithium silicates and zirconia. However, it appears that some
of these materials lack long-term scientific support and are used extensively
with only a limited understanding of optical, physical and biological material
properties. This pertains not only to material properties and fabrication
parameters, but even more clinical applications such as cementation and resin
binding protocols, which are critical to the success and survival of ceramic
restorations. Until recently, aesthetics were one of the most important motives
for choosing ceramics, but now the fabric-friendliness of the metal-free
ceramics has also been added. The patient has spoken out for biocompatibility.
The paradigm that ceramic must always be prepared and modeled differently from
metal ceramics has been eliminated with the advent of zirconia [47,48].
Digital color measurement using an intraoral
scanner is an objective and predictable method for recording the color
distribution of a tooth. However, the digital color chart is currently not yet
used by the dental technician to build up the restoration manually in layers.
In a literature review by Sailer et al. [49], for bridges on implants,
conventionally veneered zirconia should not be considered a material selection
of the first priority, due to the pronounced risk of breakage in bridges and
porcelain chipping. Thanks to developments in veneering ceramics for zirconia
and the use of strength control in the CAD design of zirconia substructures,
these problems no longer occur [50]. Monolithic zirconia, although it lacks the
natural abrasion, reflection, color from within, of a restoration veneered by a
porcelain layer, may be an interesting alternative, but the clinical results in
the medium to long term have not yet been evaluated. Only with the PRIMEROTM
CAD/CAM system [51], restorations with a zirconia substructure with dentin
shape and a milled layer of chip-resistant translucent glassceramic are
produced. For the computer-generated layer build-up, special dentin contour
shape libraries - especially the anatomy of the dentin core - are designed with
precise spatial definitions and determine the natural aesthetics of the
restoration [51]. The 2HUETM tooth shade model for these
restorations is based on research into the effect of the thickness of enamel on
the degree of masking of the internal dentin color [52]. Whether these advanced
cognitive designed CAD/CAM restorations will gain market share will depend on
the vision and imagination of investors and major market players.
In medical technology, there are ICT developments that
are far ahead of what is currently happening in dentistry, but the latter is
well on its way to catching up. We can learn a lot from this through careful
analysis, with a lot of attention to the question of what dentistry really
needs. We will have to validate every computer application and see how the ease
of use of these computer systems can be improved and how they can be integrated
into the context of dental care. Acceptance, “choosing the computer”, will
certainly not be easy in the rather traditional field of dentistry. However,
the signs are already there.
There is a need to discuss future models for the user-friendly,
efficient and cost-effective deployment of computer applications in dental
care. The contemporary resources, time and knowledge, are a highly interesting
breeding ground for a lot of innovative research.
In education, digital dentistry focuses on the
application of computer techniques and on arriving at new treatment methods and
material choices through independent analysis. Furthermore, a solid basic
knowledge of available computer techniques in the dental practice will receive
attention. A practical computer-aided techniques will fulfill an important
educational function in the scientific training.
Digital haptic and simulation systems have become important tools for
teaching dental skills. The real-time feedback through tactile sensation has
been applied to carious tissue locating and injection technique, teaching
insight into dynamic occlusion [29], locating cephalometric landmarks [52], and
drilling for implant placement [53]. While schools grapple with a declining
number of instructors, haptic systems are becoming more valuable by reducing
faculty supervision demands. While valuable, learning is best optimized through
a combination of instructor and virtual reality feedback, rather than one
replacing the other.
After more applications of the digital approach
appeared on the market, research into the reproducibility, accuracy and
correctness of the technology, which is based on point clouds, voxels and
pixels, was desired. In 2002 an initiative of the Academic Center for Dentistry
Amsterdam, a technical committee ISO/TC106/SC 9 Dental CAD/CAM systems was set
up within the International Organization for Standardization (ISO) with
approximately 30 members from 14 countries, to initiate the production of an
international standard in CAD/CAM, which eventually got its focus on the
accuracy of scanners. [54]. The work has resulted in the standard 12836:2015
Dentistry, which specifies test methods for assessing the accuracy of
digitizing equipment for computer-aided design/computer-aided manufacturing
(CAD/CAM) systems for indirect dental restorations [55].
The ambitions of the pioneers in the late 1980s
eventually led to a form of implementation, which they too could not have
dreamed of. Digital systems have penetrated our personal and professional life.
In dentistry, an essential digital dataset of patient records, X-rays,
photographs and intraoral scans, the platform represents revolutionary clinical
activities that enrich patient-dentist and interprofessional interactions,
transform education, and improve practice management. Digitization has led to
changes on many fronts and yielded new techniques, systems and interactions
that have improved dentistry. Innovation has created opportunities for future
research by materials scientists. More restorative options are available for
better durability and aesthetics. New approaches are to bring more efficiency
and accuracy, using the interests, capacities and skills of those involved. New
university curricula enable the training of students towards a new way of
learning. Digital dentistry was initially seen as a threat to dental
technicians, but this has turned out to be wrong, so much so that no one doubts
the positive contribution that the digitization of dentistry has made so far.
The question of whether 30 years of digitization has added value for dentistry
is interesting, although it has permanently changed our way of working.