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Digital Workflow in Reconstructive Dentistry Wael Att, dds, dr med dent, phd Michael Girard, rdt
Reconstructive dentistry is currently undergoing its most significant transformation since the introduction of adhesive dentistry. With the digital revolution arriving in nearly all industries and disciplines, the incorporation of digital technologies into dentistry is inevitable. The rapid and innovative shift toward digital methods is ushering in an entirely new language in the dental industry. Terms such as efficiency, lean manufacturing, measurability, consistency, mass customization, scalability, and monolithic now noticeably occupy daily conversations as the dental profession adopts tools and techniques that have been used in other industries for many years. The ultimate goal of these newly emerging technologies is to improve the quality and capabilities in examination, diagnosis, and treatment of the dental patient. Compared with conventional methods, digital workflow in the dental practice generally facilitates improved accuracy in data acquisition and assessment, superior efficacy in treatment planning, and a more controlled and faster manufacturing process. This in turn will result in a higher level of patient care and greater satisfaction for both the patient and the dentist. This chapter provides an overview of contemporary digital technologies that are implemented in contemporary dentistry, describes the current status of digital workflow and computer-aided design/computer-assisted manufacture (CAD/CAM) technologies, and gives insight about future applications.
Overview of Digital Workflow The principle of digital workflow in reconstructive dentistry comprises three main steps: (1) data acquisition, (2) data manipulation, and (3) CAD/CAM. For data acquisition, different “digitizing� techniques and devices are available. One of the essential tools is digital photography, which is widely used today for documentation and communication. Together with the appropriate software and online communication platforms, photographs can be used as a part of comprehensive treatment planning and esthetic analysis and, at the same time, as an important communication tool among the dentist,
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Digital Workflow in Reconstructive Dentistry
Fig 13-1 Digital photodocumentation enables comprehensive esthetic analysis; facilitates communication among the clinician, laboratory, and patient; and simplifies treatment.
Cerec Connect Sirona
Lava COS 3M ESPE
E4D Dentist E4D Technologies
iTero Cadent
Trios 3Shape
Fig 13-2 Some of the commercially available IOS systems.
the dental laboratory, and the patient. In cases of smile enhancement, for example, photographs and videos of different stages of the rehabilitation (try-ins, mock-ups, etc) help the dental laboratory technician to optimize the esthetic reconstruction, thus reducing the patient’s in-office treatment time during try-in (Fig 13-1). Laboratory scanners are the most widely used devices to obtain digital data from models and casts. In addition to these scanners, intraoral scanners (IOSs) are considered a technology that could replace conventional impression techniques in the future. Additional data acquisition techniques include digital facebows and digital articulators.
Intraoral Scanners Digital intraoral impressioning, intraoral scanning, and computer-aided impressioning (CAI) are terms that are currently being used to describe the process of digital scanning of intraoral structures via IOS. However, IOS are not new. The first IOS system was developed in 1980 at the 262
University of Zurich by Mörmann et al and subsequently brought to market as the Cerec system.1,2 Through the introduction of Cerec I, II, and III systems, the spectrum of applications was expanded from inlays only to onlays and single crowns. Since 2005, several other IOS systems with improved capabilities have been introduced to the market (Fig 13-2). Today, more than 15 major IOS systems are available. Although relatively similar in their workflow, the contemporary IOS systems differ in data capture and processing techniques. The rationale behind the development of IOS systems was to overcome the inherent problems associated with conventional impressions, such as improper impression tray selection, separation of impression material from the impression tray, and distortion of the impression before pouring.3 In fact, more than 50% of conventional impressions are considered inadequate in their reproduction of preparation margins.4,5 Additional goals include elimination of the need to store the impression for remaking of casts and dies as well as to improve the patient’s care and comfort and the dentist’s profitability.
Intraoral Scanners
Amplified light technology
Light technology
Light and sensor
Light and sensor
Still image capture
Still image capture
Video capture
Real-time image capture
Parallel confocal laser light imaging
Laser triangulation
Active triangulation with strip light projection
Active wavefront sampling
Ultrafast optical sectioning
iTero
E4D Dentist
Cerec Bluecam/ Omnicam
EM True Definition/ Lava COS
Trios
Fig 13-3 Different capture techniques implemented in IOS systems.
IOS data capture technologies Generally, IOS systems are based on optical scanning techniques. These techniques implement either amplified light beams (lasers) or visible light for object illumination or socalled field sampling, which is then captured and digitized via digital sensors (Fig 13-3).
Laser beam–based IOS systems Laser beam–based IOS systems depend on a still image capturing technique. In other words, the IOS captures the object by making single images at different positions. These images are later assembled and rendered into a three-dimensional (3D) object (Fig 13-4). An advantage of laser beam–based IOS systems is that they do not require the application of a reflecting agent. Two main methods are implemented in the laser beam–based IOS systems: the parallel confocal imaging technique and the laser triangulation imaging technique. These two laser techniques are explored as separate topics to better explain the scanning methodology.
Parallel confocal imaging technique. The so-called parallel confocal imaging technique is derived from micro scopy. Here, parallel laser beams are sent through the scanning head, hit the object at specific focal length, and bounce off and back through a small hole. Then the reflected beams hit the laser sensor and are converted into a digital image. A representative system that implements this technique is iTero (Cadent). The system projects 100,000 beams of parallel red laser light at 300 different focal depths that are spaced approximately 50 μm apart. In this way, a field of 14 × 18 mm is sampled within one-third of a second and the data are then digitized.6,7 The spacing allows for an approximate scan depth between 13 and 15 mm. In total, the system captures approximately 3.5 million data points for each arch that is scanned.8 Laser triangulation imaging technique. In the laser triangulation imaging technique, a red laser beam is emitted, and micro mirrors that oscillate at 20,000 cycles per second capture a series of still images from multiple angles around the object. The captured images are rendered into a virtual 263
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Digital Workflow in Reconstructive Dentistry
a
b
Fig 13-4 (a and b) Rendered 3D data from an IOS (iTero).
3D object.7,9 The laser triangulation technique is similar to the triangulation technique implemented in light beam– based IOS systems. A representative IOS system that utilizes this technique is the E4D system (E4D Technologies).
Light beam–based IOS systems The second group of IOS systems employs visible light beams, instead of laser beams, for image capture. In this group, the image capturing techniques can be still image capture (active triangulation), video capture, or real-time image capture. The majority of IOS systems that belong to this group require the application of titanium dioxide as a reflecting agent. Active triangulation technique. In the active triangulation technique, the intersection of three linear light beams is used to locate a given point in a 3D space.10 However, surfaces that disperse light irregularly do not reflect it evenly, and irregular surfaces, namely tooth surfaces, adversely affect the accuracy of scanning based on triangulation.11,12 Therefore, a coating powder (titanium dioxide) is required to provide uniform light dispersion and to enhance the accuracy of the scan. Active triangulation techniques are implemented in the Cerec AC/Bluecam system (Sirona). The camera emits a varying pattern of blue light (wavelength of 470 nm) onto the dentition, and the reflective light is read back at a slightly different angle, ultimately creating a digitized cast. While 264
previous versions of these scanners implemented red light (wavelength of 820 nm), the shorter wavelength of blue light enables for a larger depth of field and is claimed to improve scanning accuracy by about 60%.12,13 The shutter speed of 17 milliseconds per image further reduces the risk of blurring, as does the option to rest the camera on the teeth. With a depth-of-field range of 14 mm, excellent focus can be obtained during imaging. The wavelength of blue light also facilitates distortion-free imaging.10,13 While the original Cerec IOS system was solely indicated for digital image acquisition meant for fabrication of singleunit all-ceramic restorations using Cerec’s proprietary inoffice milling system, the latest generation allows the user to transmit the data to the dental laboratory for laboratory production.11 Active wavefront sampling technique. Another method for image capturing involves active wavefront sampling (AWS). Unlike still image capture, AWS technology captures 3D data in a video sequence and models it in real time.7 Based on defocusing of the primary optical system, the AWS technique obtains 3D information from a single-lens imaging system by measuring depth. The continuous video capturing technique is more user-friendly than the still image capturing technique because both the need to fix the scanning wand at a specific aspect for capturing and the process of assembling the images into a 3D object are eliminated.
Intraoral Scanners Fig 13-5 The Lava COS system incorporates 192 blue light–emitting diodes and 3 complementary metal-oxide semiconductor sensors that facilitate AWS capture at a rate of 20 3D datasets per second.
The technique is implemented in both the Lava COS system (3M ESPE) and the newer 3M True Definition Scanner (3M ESPE). The Lava COS system incorporates 192 blue light–emitting diodes for illumination and 3 sensors that capture the object from different perspectives simultaneously (Fig 13-5); that is, three different images are being captured at a time. Then, the 3D surface patches are generated in real time by means of a proprietary image processing algorithm using the in-focus and out-of-focus information.7,9,14 The system captures 20 3D datasets per second, each containing 10,000 data points of information, resulting in more than 2,400 datasets (or 24 million data points).9 The Lava COS has a field of view of approximately 10 × 13.5 mm.7 Ultrafast optical sectioning technique. Similar to the video capturing technique (ie, AWS), ultrafast optical sectioning technology facilitates continuous image capture. Rather than artificially forming interpolated surfaces, the technique utilizes up to 1,000 3D images to create true geometries based on real data. This technology is being implemented in the Trios IOS system (3Shape). According to the manufacturer, the scanner captures more than 3,000 two-dimensional images per second, which is 100 times faster than a conventional video camera. Unlike other light beam–based IOS systems, the Trios system does not require the application of a reflecting agent. Although information about the depth of field is not disclosed by the manufacturer, the scanner functions
completely independently of motion and position. In other words, there is no need to hold the scanner at a specific distance or angle for focus, and the scanner can be placed on the teeth for support during scanning.
Efficacy of IOS systems IOS systems provide several advantages over conventional impressions. These include elimination of the need for impression trays and materials, the ability to evaluate the quality of the scan results immediately after the scan is completed, and the ability to create a digital archive of patient records. Rather than repeat the entire digital impression, the user is able to add to an existing scan if information is missing. Patient response to this technology is usually reported as outstanding because the unpleasant experience of analog impressions is eliminated. However, the efficacy of IOS systems is best assessed by comparison to conventional impressions in terms of accuracy and time saving. Although only a small number of studies are available, the accuracy of CAI systems seems to be similar to that of conventional impression taking.13,15,16 For complete-arch impressions, the accuracy of conventional impressions has been reported to be approximately 55 µm, while the accuracy of CAI has been reported to range between 40 and 49 µm.13,15,16 When the different steps needed for fabrication of restorations via the two techniques are compared, IOS systems seem to require essential steps similar to those required 265
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CONVENTIONAL Preparation of tray
Retraction cords
Impression
Disinfection
Send to laboratory
Pouring
Master cast
Fabrication of restoration
(Virtual) master cast
Fabrication of restoration
DIGITAL Scanner preparation
Retraction cords
Scan
Send to laboratory
Fig 13-6  Comparison of clinical and laboratory steps required by conventional impressions and IOS systems (digital).
Fig 13-7  Clinical procedure for CAI. Ideal abutment isolation is critical for an accurate scan.
with conventional impressions; however, two steps are eliminated with IOS systems (Fig 13-6). Whenever equigingival or subgingival preparations are present, the placement of retraction cords is considered an essential step. The placement of retraction cords and achievement of proper isolation seem to be more critical with CAI than with conventional impressions (Fig 13-7). IOS systems are all based on optical scanning technologies, meaning that all preparation margins must be visible to the scanning wand to facilitate an ideal reading. If, for instance, the soft tissue is visually covering a deep subgingival preparation, the light beam emitted from the IOS system will be blocked by this tissue and thus the covered area cannot be scanned (Fig 13-8). When conventional impressions are used in similar cases, the impression material still can flow into the preparation area and provide a good marginal reading. Such clinical difficulties are often encountered in areas where subgingival preparations are present, that is, in the esthetic zone, where there is a need to conceal the restora266
tion margins. Therefore, it can be assumed that CAI might be more challenging than conventional impression taking in situations where the preparation margins are located deep within the sulcus.
Clinical application of IOS systems The principle of CAI is similar among different IOS systems. After the teeth have been prepared, retraction cords are placed to provide visualization of the preparation margins during the scanning process. Therefore, whenever subgingival preparations are present, the dual-cord retraction technique may be helpful for CAI using IOS systems. For implant restorations, CAI usually requires the use of a scan body that can be connected to the implant during the scanning process (Fig 13-9). After scanning of the prepared and adjacent teeth is completed, the opposing arch is scanned. Then the patient is instructed to close into maximal intercuspal position, and the relationship of the occluding teeth is captured. The ac-
Intraoral Scanners Fig 13-8 Clinical situation in which the application of an intraoral scanner is limited. Gingival tissues covering a deep preparation will block the light beam emitted from the IOS system, and thus an ideal reading cannot be obtained.
a
b
Fig 13-9 (a) Use of scan bodies during the scanning process for dental implants. (b) The scan bodies help the scanning software to identify the 3D position of the implants. (Courtesy of Dr Petra Guess, Freiburg, Germany.)
quired data are assembled by the software to render 3D objects of the scanned teeth as well as the occluding surfaces. Finally, the maxillary and mandibular scans are digitally articulated and displayed on the screen.7,17 The next step is system dependent. For the in-office manufacturing systems, the acquired data can be manipulated by CAD software that is provided by the manufacturer of the IOS system. This process can be carried out in the dental office or in the local dental laboratory. The data for the designed restoration can then be transferred to the milling unit in the dental office or the local dental laboratory to fabricate frameworks or the entire monolithic ceramic unit. For IOS systems only intended for CAI, the acquired data must be transferred via upload to the manufacturer’s server for further processing before CAD can take place. Whether
it is an open or a closed system, the manufacturer usually charges fees for data processing or conversion, termed click fees. Once the manufacturer has received the data, a cleaning process to remove artifacts from the scan data is carried out. Then the data are sent to the local laboratory or the design center for CAD. With closed systems, both the CAD software and the CAM process are provided by the same manufacturer of the IOS system. With open systems, the clinician can select the CAD software and CAM process of preference. In this case, the scan data will be converted by the manufacturer into the standard tessellation language, known as the STL file format, which is a universal data format supported by many rapid prototyping and CAD software systems. Although universal, the STL data format is not read the same way by 267
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Digital Workflow in Reconstructive Dentistry TABLE 13-1 Overview of different features of commercially available IOS systems* System Cerec AC Omnicam
iTero
Lava COS/3M True Definition
Trios
E4D
Manufacturer
Sirona
Cadent
3M ESPE
3Shape
E4D
System
Closed
Selectively open
Selectively open
Open
Closed
Model fabrication
Additive/subtractive/ stereolithography
Subtractive/milling
Additive/stereolithography
Subtractive/milling Additive/ stereolithography
Virtual
Restorative options
Inlays, onlays, partial crowns, veneers, crowns, 3- to 4-unit FDPs, implants
Inlays, onlays, partial crowns, veneers, crowns, 3- to 4-unit FDPs, implants
Inlays, onlays, partial crowns, veneers, crowns, 3- to 4-unit FDPs, implants
No limitations
Inlays, onlays, partial crowns, veneers, crowns
Need for reflecting or connecting agent
No
No
Yes
No
No
Restoration fabrication
Chairside Individual laboratory
Milling center Individual laboratory
Milling center Individual laboratory
Milling center Individual laboratory
Chairside
Weight of handpiece
313 g
1,120 g
397 g
625 g
420 g
Feature
*Information provided by the manufacturers. FDPs, fixed dental prostheses.
Fig 13-10 Casts produced from CAI data obtained with different IOS systems. (top row, left to right) Cerec (subtractive), iTero (subtractive), and Lava COS (additive manufacturing; stereolithography). (bottom row) Specific characteristics of the produced casts related to the manufacturing technique.
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Intraoral Scanners TABLE 13-2 Current potential applications of IOS systems Restorations
Intraoral scan
Notes
Inlays, onlays, veneers, and single crowns
Possible
Esthetics demanding with anterior crowns
Fixed dental prostheses
Possible
Does not save time; esthetics demanding with anterior FDPs; non–facebow-based mounting
Implant restorations
Possible, but not for all systems
Needs implant scan bodies
Removable dental prostheses
Possible, but not for all systems
Software limitations
Splints
Possible, but not for all systems
Software limitations
Complete dentures
Not possible
Hardware limitations
Surgical guides
Possible, but not for all systems
Software limitations
FDPs, fixed dental prostheses.
different CAD software, because processing algorithms are different among different software programs. Therefore, the manufacturer of an open IOS system usually requires exact information about the CAD software to be used in order to perform a software-compatible STL conversion that facilitates accurate reading of the surface geometry and rendering of the 3D objects. Once converted, the data are sent back to the dental laboratory or the design center to complete the CAD process and manufacture the restorations. With the selectively open systems, the workflow is similar to that associated with the open systems. However, further processes must be performed, primarily with CAD software and CAM hardware from the same manufacturer of the IOS system. Should the dentist or laboratory technician request to work with CAD software that is different from that provided by the IOS manufacturer, the manufacturer must then convert the data to a standard STL file format, and additional click fees may be applied.
Cast fabrication The majority of IOS systems provide the possibility to fabricate casts from the scan data. Depending on the IOS system, these casts can be fabricated by either subtractive or additive (rapid prototyping) techniques (Table 13-1). For the subtractive technique, a plastic- or resin-based material is milled to fabricate the casts. For additive manufacturing, stereolithography is currently the method of choice. Here, layers of liquid resin are added sequentially and photopolymerized to produce the cast (Fig 13-10). The produced casts can be used in further processing (conventional fabrication) or as a communication tool among the dentist,
patient, and laboratory technician. Although nearly no studies about the accuracy of digitally fabricated casts are available yet, clinical experience has shown the quality of accuracy to vary among different systems.
Current indications for and future possibilities of IOS systems While the first generation of IOS systems was only usable for the fabrication of inlays, the contemporary IOS systems offer the possibility to fabricate a wide spectrum of fixed restorations, including inlays, onlays, veneers, single crowns, and fixed dental prostheses (Table 13-2). Due to the current software and hardware configurations, four- to five-unit fixed dental prostheses are considered to be the limit for nearly all IOS systems. Depending on the system, the options for restorative materials can include resins, nonprecious metal alloys, ceramics, and high-strength ceramics. The fabrication process can be either subtractive (milling or grinding) or additive (stereolithography, 3D printing, selective laser sintering, etc). For high-strength ceramic restorations, the currently available fabrication techniques are subtractive procedures. All IOS systems, including related CAD/CAM techniques, are limited to partial edentulism. In other words, there is currently no possibility to implement CAI for the fabrication of complete dentures. Thus, the current potential of IOS systems, their relatively narrow indication spectrum, and their high cost-benefit ratio, have limited their acceptance and widespread growth in dental practices. Hence, the current IOS systems should be considered as a blueprint for future systems. Current research is focusing on the expansion of the indication spectrum of IOS systems to include edentu269
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Digital Workflow in Reconstructive Dentistry Fig 13-11 Principle of a five-axis scanner. Two cameras are combined with a three-axis rotation mechanism. The multiaxis scanning process enables the identification of sophisticated anatomical structures.
lous jaws. Once this methodology is established, the fabrication of removable dental prostheses, including complete dentures, would be possible using IOS systems. More interesting, the introduction of advanced imaging technologies that are being used in other medical disciplines, such as optical coherence tomography (OCT), will facilitate the potential for IOS systems to perform transgingival scans.18 OCT is a below-infrared–based imaging technology that is already being implemented in the medical field to obtain high-resolution images of the retina and eye. The main advantage of this technique is that it provides subsurface images of translucent or opaque materials at a resolution equivalent to that achieved by a low-powered microscope. When OCT is successfully applied in IOS, CAI can be performed without the mandatory placement of retraction cords. With such innovations, CAI will rapidly replace conventional techniques.
Laboratory Desktop Scanners Desktop scanners have been used in dental laboratories for more than 20 years. While early scanning devices utilized touch probe (tactile) scanning, contemporary scanners utilize optical technologies. Compared with early versions, 270
currently available optical desktop scanners have vastly improved in all facets—speed, accuracy, and scanning capabilities. Laser scanning and optical-stripe light projection represent the optical measurement technologies primarily deployed for the 3D digitization of the surface of a dental cast or impression. They are both based on the same rule, namely triangulation, in the way that light structures (normally in the form of stripes) are projected onto the object, where light sensors acquire the image; by known geometry of the setup, 3D information can then be drawn from the imaged data. The difference between the two methods resides in the way the light structure is projected and imaged. In laser scanning, laser light sources are used to project one or multiple thin and sharp stripes onto the scanned object, whereas in optical-stripe light projection systems, light patterns (usually in the form of a bundle of stripes) are projected onto the entire object being scanned. While laser scanners were previously considered to provide higher resolution and accuracy, both methods today offer a precision of 10 µm or less. The spectrum of applications of current desktop scanners varies from scans of individual dies to scans of arch segments, complete-arch casts, impressions, bite records,
Virtual Articulation Fig 13-12  Multiaxis desktop scanners. (a) D700 System (3Shape). (b) 7 Series Scanner (Dental Wings). This type of scanner can be used to scan complex and large complete-arch cases. The embedded high-resolution cameras are usually intended for texture scanning.
a
wax-ups, and articulators. To improve the accuracy of the scan, some scanners require the application of a reflecting agent, while others require the use of casts made of a scannable gypsum. Newly introduced scanners include high-resolution cameras that allow for adaptive impression scanning as well as texture-capture capabilities. Usually, the scanner features at least two capture devices (two cameras or two laser sensors) that are attached to a three-axis rotation mechanism. In five-axis scanners, the objects are additionally attached to a rotating mechanism, allowing the object to be rotated and thus adding two additional axes. This motion feature enables the capture devices to effectively detect the object from any viewpoint; scan all details of the object, including undercuts; increase the size of the measuring field; and improve the overall accuracy of the scan data (Figs 13-11 and 13-12).
Virtual Articulation For many dentists and dental technicians, the concept of creating a crown without the guidance of a simple hinge articulator that captures centric occlusion is unthinkable. Even in the virtual world, most of the current CAD software applications have been able to adequately accommodate simple management of occlusion. Until recently, however, CAD applications had limitations for the design of multiple or complex restorations where dynamic occlusal management was critical to the success of the case.
b
In general, CAD software can be divided in regard to its capabilities for virtual articulation: basic, advanced, and individual.
Basic virtual articulation The basic category is considered the simplest method for virtual articulation, and for a long time it was considered the sole solution for virtual articulation. Here, partial models of the abutment and adjacent teeth are used. The opposing jaw is then correlated via a scanned check-bite that is positioned over the main model (Fig 13-13). In IOS systems, the patient is instructed to close into the maximal intercuspal position, and the image of the occluding teeth is captured from the lateral aspect. The generated 3D data can be then articulated virtually. Apart from opening and closing movements, simulation of jaw movements is not possible in this category.
Advanced virtual articulation (non–facebow-based mounting) In advanced virtual articulation, the partially or completely scanned casts, or jaws in case of an intraoral scan, can be articulated via a lateral scan of the occluding teeth. The software matches and mounts the jaws virtually without the need for any further references. Based on average values, jaw movements can be simulated.
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Fig 13-13 Basic virtual articulation procedure. The opposing arch is then correlated via a scanned check-bite that is positioned over the main model.
Fig 13-14 Advanced virtual articulation using an IOS system (iTero). Non–facebowbased mounting provides no individual references (planes, lines, etc).
Fig 13-15 Individual virtual articulation (S600 Arti, Zirkonzahn). The scanner allows scanning of the mounted casts together with a real articulator. All information and individual references (planes, lines, etc) that are obtained from the facebow transfer as well as conventional registration procedures can be digitized and transferred to the CAD software.
While this technique can be acceptable for single and small-unit restorations, it cannot be applied to completearch reconstructions because this type of mounting provides no information about individual reference planes and lines. In other words, the virtual articulation in this category is considered as a non–facebow-based mounting procedure that does not have any individual references (Fig 13-14). For complete-arch reconstructions, it is important to perform a facebow-based mounting to provide valuable information about individual references, which are essential for the fabrication process of properly functional and esthetic restorations. 272
Individual virtual articulation (facebow-based mounting) In individual virtual articulation, after scanning of the casts is completed, they are automatically loaded into a semiadjustable virtual articulator. In other words, the digital models in this category are not placed in an empty virtual space but rather in relation to an articulator. The virtual mounting is achieved either by fixing the models with an alignment key or a special cap in the scanner. After the scanning process, the software loads the models into the articulator and mounts them based on average values.
Computer-Aided Design Fig 13-16  Individual virtual articulation (3Shape). In addition to the inclusion of individual references of the clinical case, the software provides the option to select the articulator of choice and customize the values according to individual needs.
Another option is to scan the individual casts first and then scan the mounted casts together with a real articulator (Fig 13-15). Then the software matches the individual virtual models with the mounted ones. This way, all information and individual references (planes, lines, etc) that are obtained from facebow transfer as well as conventional registration procedures can be digitized (Fig 13-16). To optimize the occlusal design and ultimately improve functionality, the software provides the option of customizing all values in the articulator, such as height, side shift, Bennett angle, and excursion. While the individual virtual articulation technique is possible with desktop scanners, it is difficult to perform with IOS systems (see Fig 13-14). IOS CAD software does not yet offer the possibility of integrating the individual references and values needed for individual virtual articulation. In other words, unless real casts are fabricated, digitized using desktop scanners, and virtually articulated as already described, complete-arch reconstructions are difficult to fabricate using the virtual articulation possibilities of IOS systems. Because of such technically demanding workflow, at this point in time all contemporary IOS systems are indicated only for the fabrication of single crowns and four- to five-unit fixed dental prostheses. The innovations in virtual articulation have enabled technicians and dentists to work with specific models of semiadjustable articulators. While work still needs to be done to facilitate accurate transfer of facebow records to the software, recent advancements have significantly reduced or
even eliminated time-consuming adjustments to the occlusal surface of digitally manufactured restorations. Continued improvements in this area may increase confidence in the manufacture of complete-mouth restorations and perhaps even model-free crowns.
Computer-Aided Design Computer-aided design is the use of a computer to assist in the creation, modification, analysis, or optimization of a design. CAD software is used to improve the productivity of the designer, the quality of the designs, and the communication through documentation as well as to create a database and a 3D file for manufacturing. CAD software is either open or closed. While closed CAD software uses various industrial file formats that are system specific, the STL file format is the most commonly used language for open CAD software. As mentioned earlier, STL is supported by many software packages and commonly used for both additive (rapid prototyping) and subtractive manufacturing technologies (milling or grinding). Once the teeth, impressions, or casts are scanned and virtually articulated, an experienced user can move from order creation to completed design of a single coping or crown, ready for manufacturing, in just a few minutes. Thanks to contemporary CAD/ CAM technologies, a single technician in a large laboratory equipped with advanced CAD/CAM systems could design as many as 100 units per day. 273
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Digital Workflow in Reconstructive Dentistry The CAD process is considered easy and at the same time a very important step for the success of the restoration. Once the scanning process is completed, contemporary CAD software will automatically create a default design file of the restoration so that further steps become a process of simply fine-tuning the system’s design suggestions using virtual sculpting tools or changing the design parameters. These design parameters include but are not limited to material thickness restrictions and blockout for undercuts and sharp angles. The software may even allow the user to direct what tools are used and in what sequence during the CAM process. Intuitive tools used in the CAD process enable the designer to create and edit morphology, optimize mechanical and esthetic properties, and quickly achieve sophisticated designs for prosthetic frameworks and fully anatomical restorations. Upcoming innovations in CAD software will include significant improvements in design automation, thus simplifying the procedure and accelerating the manufacturing process. Also, future developments will introduce more and more open CAD software, thus providing the laboratory technician and the clinician with the freedom to select the manufacturing system as well as material and easing communication among different laboratories and manufacturers.
Computer-Assisted Manufacture Once the CAD process is complete, the generated files are transferred to a local or a remote CAM facility. Here, a software and process are required to enable fully automated manufacturing of dental restorations by preparation of the generated CAD files for milling, wax printers, modelmaking machines, and/or laser sintering. CAM software programs guide the technician through the processing of STL files, including autodetection of margin lines and undercut reduction. The user can also configure automatic sorting of completed designs based on manufacturingspecific parameters, such as material, manufacturing equipment, and height. While early versions of CAM software were limited to setting of material selection, new versions include features for automatic preparation of the completed design such as the addition of sprues or drops and optimal placement of the virtual restoration in the material blank for milling or printing. This process is termed nesting (Fig 13-17). New developments in CAM software enable tracking and reuse of partially milled material blanks from previous jobs. CAM can be divided into two categories: (1) additive manufacturing, such as wax printing and laser sintering,
274
and (2) subtractive manufacturing, which includes milling or grinding.19
Additive manufacturing For rapid prototyping machines, such as wax printers and model-making machines, CAM software can automatically process all preparation steps, including optimal placement, orientation, support generation, and communication with the machine. Innovation in this software has enabled adaptive grouping with automatic clustering of cases (eg, from the same laboratory) for efficient handling. Fully automated preparation of completed designs for laser sintering machines is also available, including optimal placement, unique support generation, and identification tags. The unique support structure suppresses warping during the sintering process but is still easy to remove. Adaptive grouping is also provided for laser sintering. While additive manufacturing technologies for highstrength ceramics are still under development, they are not discussed further in this chapter.
Subtractive manufacturing The subtractive manufacturing process for dental restorations was first introduced to dentistry almost 25 years ago. Since then, the landscape has changed significantly. Today, technicians and dentists are able to automatically design teeth, detect the margins, and automate occlusion at chairside or in the dental laboratory. Once that design has been completed, an output device is needed to process the material of choice. In general, the subtractive manufacturing process can be carried out using two techniques. The first technique involves milling of enlarged frameworks out of homogenous ceramic blanks (namely zirconia), which are usually delivered in a nonsintered (green body) or in different presintered stages. The milled frameworks are then sintered and shrunk to the desired dimensions.20–22 The second technique consists of grinding the frameworks directly to their final dimensions out of densely sintered prefabricated blanks.20–23 Compared with the milling technology, the latter technique has been reported to be associated with a frequent need to change the grinding tools as well as a longer time to produce the frameworks.20 Although no clinical data are available yet, it can be expected that different fabrication and processing techniques for frameworks influence their resistance (eg, resistance of zirconia to low thermal degradation property), which in turn will affect the clinical behavior of the restoration.24 For these reasons, most manufacturers today adopt the milling
Computer-Assisted Manufacture
a
b Fig 13-17  CAM processing and nesting of multiple STL files in preparation for milling. (a) Completecontour zirconia crowns (Diadem Precision Technology). (b) Fixed dental prostheses (Nesting Software, Zirkonzahn).
manufacturing technology rather than the grinding technology. A plethora of subtractive fabrication machines are available now in every size, capability, and price, targeting both dental laboratories and clinicians. Most desktop CAM machines are of the three- or fouraxis variety. These machines are typically designed to handle light volumes but are capable of milling most restorations as long as the geometry is not too complex. Newer versions of desktop machines include five-axis milling, enabling the fabrication of structures with improved surface quality and allowing development of undercuts and
complex geometries. Five-axis machines can control tool motion in three linear axes and two rotary axes. Compared with desktop CAM machines, industrial CAM machines located in production centers are all based on five-axis manufacturing. In addition, they are often larger, faster, and more robust; have higher accuracy and repeatability than desktop CAM machines; and can be automated with robotics for loading and unloading of the machine. Manufacturers of such CAM units report that they can be calibrated with repeatable 5-Îźm accuracy.
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Digital Workflow in Reconstructive Dentistry
Conclusion It is clear that contemporary digital technologies are rapidly emerging in the dental profession. New materials, new technologies, and new processes will most certainly continue to impact how dental professionals treat patients and fabricate and deliver restorations as well as how fast that treatment is accomplished. Future developments will provide solutions to issues that are associated with the currently available technologies (such as the difficulties in fabricating complete-mouth prostheses) and will enhance the interface between different components of the digital workflow. In addition, open systems are expected to dominate the CAD/CAM industry because they offer easy communication among different laboratories, production centers, and clinicians. Ultimately, this coordination will ease the integration of the digital process in dentistry and increase the number of users, resulting in a higher level of patient care and better satisfaction for both the patient and the dentist. As with most technologic innovations, increased utilization is also likely to drive down prices, making these systems more affordable to more dental professionals. In other industries such as the mobile telephone business, digital innovations are disrupting the delivery of services and economics almost daily. Hardware manufacturers
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are faced with increasingly demanding consumers who are willing to pay for the minutes but not the telephone. The hardware manufacturers have been forced to be creative in the delivery of their systems. Carriers work in partnership with manufacturers to offer the hottest new telephones at enticing subsidized prices, but they do so to encourage folks to sign up for a long-term commitment that entails high penalty fees for early termination. Similarly, the dental world may soon see creative usage plans like those in the mobile telephone world. The adoption of digital impression devices has been a slow process. Manufacturers of IOS may need to look for ways to bundle the delivery of services and products into the cost of the device. Dental laboratories also may have to get creative and develop plans that bundle their services and product offerings to defray the cost of the hardware to the dentist. In other words, dentists may soon be able to source their device of choice from a laboratory but may have to sign a contract agreeing to the purchase of a product or service, in essence locking them into the use of that laboratory. As the dental profession adopts and optimizes digital tools and techniques, the quality of examination, diagnosis, and treatment of the dental patient will continue to improve. The profession of dentistry is moving from an era in which anything is possible to an era in which everything is probable.
References
References 1. Mörmann WH. The evolution of the CEREC system. J Am Dent Assoc 2006;137(suppl):7S–13S. 2. Mörmann WH, Brandestini M, Lutz F, Barbakow F. Chairside computer-aided direct ceramic inlays. Quintessence Int 1989;20: 329–339. 3. Stein JM. Stand-alone scanning systems simplify intraoral digital impressioning. Compend Contin Educ Dent 2011;32(special issue 4): 56,58–59. 4. Christensen GJ. The state of fixed prosthodontic impressions: Room for improvement. J Am Dent Assoc 2005;136:343–346. 5. Christensen GJ. Impressions are changing: Deciding on conventional, digital or digital plus in-office milling. J Am Dent Assoc 2009; 140:1301–1304. 6. Henkel GL. A comparison of fixed prostheses generated from conventional vs digitally scanned dental impressions. Compend Contin Educ Dent 2007;28:422–431. 7. Birnbaum NS, Aaronson HB. Dental impressions using 3D digital scanners: Virtual becomes reality. Compend Contin Educ Dent 2008;29:494–505. 8. Garg AK. Cadent iTero’s digital system for dental impressions: The end of trays and putty? Dent Implantol Update 2008;19(1):1–4. 9. Kachalia PR, Geissberger MJ. Dentistry a la carte: In-office CAD/ CAM technology. J Calif Dent Assoc 2010;38:323–330. 10. Pieper R. Digital impressions—Easier than ever. Int J Comput Dent 2009;12:47–52. 11. Ender A, Mehl A. Full arch scans: Conventional versus digital impressions—An in-vitro study. Int J Comput Dent 2011;14:11–21. 12. Steinbrenner H. The new Cerec AC Bluecam recording unit: A case report. Int J Comput Dent 2009;12:71–77.
13. Mehl A, Ender A, Mörmann W, Attin T. Accuracy testing of a new intraoral 3D camera. Int J Comput Dent 2009;12:11–28. 14. Rohaly J. The development of the Lava chairside oral scanner C.O.S. technology—Masterstroke of a legion of talented and committed people [interview]. Int J Comput Dent 2009;12:165–169. 15. Persson A, Andersson M, Oden A, Sandborgh-Englund G. A threedimensional evaluation of a laser scanner and a touch-probe scanner. J Prosthet Dent 2006;95:194–200. 16. Syrek A, Reich G, Ranftl D, Klein C, Cerny B, Brodesser J. Clinical evaluation of all-ceramic crowns fabricated from intraoral digital impressions based on the principle of active wavefront sampling. J Dent 2010;38:553–559. 17. Fasbinder DJ. Digital dentistry: Innovation for restorative treatment. Compend Contin Educ Dent 2010;31(special issue 4):2–11. 18. Gutierrez-Chico JL, Alegria-Barrero E, Teijeiro-Mestre R, et al. Optical coherence tomography: From research to practice. Eur Heart J Cardiovasc Imaging 2012;13:370–384. 19. van Noort R. The future of dental devices is digital. Dent Mater 2012;28:3–12. 20. Raigrodski AJ. Contemporary materials and technologies for allceramic fixed partial dentures: A review of the literature. J Prosthet Dent 2004;92:557–562. 21. Sadan A, Blatz MB, Lang B. Clinical considerations for densely sintered alumina and zirconia restorations. 1. Int J Periodontics Restorative Dent 2005;25:213–219. 22. Sadan A, Blatz MB, Lang B. Clinical considerations for densely sintered alumina and zirconia restorations.t 2. Int J Periodontics Restorative Dent 2005;25:343–349. 23. Vult von Steyern P. All-ceramic fixed partial dentures. Studies on aluminum oxide- and zirconium dioxide-based ceramic systems. Swed Dent J Suppl 2005;173:1–69. 24. Chevalier J. What future for zirconia as a biomaterial? Biomaterials 2006;27:535–543.
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