Bites for the Computer: Thirty Years of Digitization in Dentistry

• By comparing the motivation of the pioneers with the new state of the art of digital dentistry, it gives a good picture of the type and extent of innovations and technological advancements in the last 30 years that have been of influence and whether dentistry was improved by progress and innovations, the breadth and their impact, disruptions and benefits that have or have not occurred and whether material scientists have seized all opportunities. 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 into new materials.
• Due to digitization and the new state of the art, the patient experience has improved. More restoration options are possible with high durability and better aesthetics. New ways have been developed for effective and efficient interprofessional and clinical-patient interactions. 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 incorrect, so much so that no one doubts the positive contribution that the digitization of dentistry has made anymore. The question of whether 30 years of digitization has added value for dentistry is interesting, although it has permanently changed our way of working.

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 (CEREC^TM) [4], Rekow [7], Van der Zel (CICERO^TM) [5], Anderson (PROCERA^TM) [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 CEREC^TM, 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 CEREC^TM system, and a triangulation laboratory scanner integral with the CICERO^TM 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 CICERO^TM 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 0.25^o 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 PRIMERO^TM 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 2HUE^TM 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.

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