Читать книгу Digital Workflow in Reconstructive Dentistry - Группа авторов - Страница 10
ОглавлениеThe evolution of computer-aided impression-making occurred almost simultaneously with major developments in dental computer-aided design/computer-aided manufacturing (CAD/CAM). In the 1970s, dentists John Young and Bruce Altschuler first attempted to introduce CAD/CAM technology into dentistry, developing an intraoral grid mapping system using an optical apparatus.1 Dr. Francois Duret developed and patented the first CAD/CAM device in 1984.2-4 Two years later, at the Chicago Midwinter Meeting in 1989, the device, called Sopha System (Sopha Bioconcept, CA, USA), was officially and publicly launched. During this meeting, a crown fabrication was demonstrated and it took four hours to be completed.5 Prior to crown design and milling, an optical impression of an abutment tooth had been performed. The optical impression could be obtained either extraorally from a dental casting gypsum model, or intraorally by a 512 × 512 pixel charge-coupled device (CCD) camera, using a method derived from electronic Moiré patterns.3,6 Several factors, such as complexity and cost, impeded the success of the system in the dental market.3,7 In 1980, Dr Werner Mörmann and an electrical engineer, Marco Brandestini, developed a CAD/CAM system that was introduced in 1987 as Cerec (Chairside Economical Restoration of Esthetic Ceramics) by Sirona Dental Systems, Bensheim, Germany. At that time, Cerec was considered the first commercially available CAD/CAM system for the fabrication of dental restorations that utilized a compact intraoral 256 × 256 pixel CCD camera for data acquisition.4,8,9 The NobelProcera system (Nobel Biocare, Gothenburg, Sweden) was developed by Dr Matts Andersson as a result of his efforts to fabricate titanium copings. The data for the CAD/CAM process was obtained from a stone cast (master die) via digitizing by means of a tactile scanning device.10,11
The developers of Cerec have set as a goal the proper functional, biological, and esthetic prosthetic restoration of teeth within a single visit.12 Its introduction enabled the fabrication of inlays, while later versions, Cerec II and III, facilitated the fabrication of onlays and single crowns. Since 2005, several other intraoral scanners (IOSs) with improved features have been introduced into the market (Fig 2.1). In recent years, the market of IOS systems has been grown increasingly with the introduction of new devices as well as developments to existing systems (Fig 2.2, Table 2.1).
Fig 2.1 Overview of the currently available and most frequently used IOS systems.
Fig 2.2 Several commercially available IOS systems. With new models, the device’s footprint is becoming significantly smaller.
Table 2.1 Overview of different features of recently launched intraoral scanner systems (adapted from Zimmerman et al.19). Features and fees of different systems may vary
Overview of the Digital Workflow
As described earlier in the first chapter of this book, the digital workflow is composed of three components: data acquisition (e.g., computer-aided impression), data manipulation (CAD), and fabrication (CAM) or execution of treatment. From a technological aspect, the CAD/CAM technology can thus be divided in three separate concepts. The first includes a complete chairside CAD/CAM system in the office, where the practitioner can scan the prepared teeth, design the restorations, and manufacture them in the operatory during a single patient visit. The second concept facilitates scanning the prepared teeth and designing the final restoration. Further milling and manufacturing are performed in the laboratory. The latter option focuses only on data acquisition via scanning/digital impression and the practitioner must send the information to a traditional dental laboratory or to a designated CAD/CAM laboratory for the construction of the restoration.
In other words, some IOSs can be used to solely acquire data, while others are intended to acquire the data and also allow the clinician to design the restoration. Obviously, these features relate to the proprietary software of each device and the workflow strategy of the manufacturer.
The development of IOS systems resulted from the continuous attempt to overcome problems inherent to conventional impressions, such as improper impression tray selection, separation of impression material from the impression tray, and distortion of the impression before pouring.13,14 In fact, more than 50% of conventional impressions are considered as inadequate in terms of reproduction of preparation margins.15,16 Additional motivating factors are the elimination of the need to store the impression for remaking of casts and dies, as well as improvements to the patient’s care and the dentist’s income.13 The process of digital scanning of teeth and/or implants and the surrounding soft and hard structures using specific devices (IOSs) has been described by several terms, such as digital intraoral impression, intraoral scanning, and computer-aided impressioning (CAI).
Today, there are more than 22 major IOS systems available, which all exhibit a relatively similar workflow and largely differ in data capturing and processing techniques. Interestingly, it became usual to find the same hardware product sold under different names, perhaps with a proprietary three-dimensional (3D) scanner software and/or payment plan.17 For example, the visual difference between the Cyrtina IOS (Oratio, the Netherlands), the i/s/can appliance (Goldquadrat, Hanover, Germany), the detection eye (Zirkonzahn, South Tyrol, Italy), the Organical oral scan (R+K, Berlin, Germany), and the 3D progress (MHT, Verona, Italy) can be found only by the logo and perhaps color variant.17
Generally, IOS systems are based on optical scanning techniques. These techniques implement either visible light or an amplified light beam (laser) for object illumination or utilize so-called field sampling, which is then captured and digitized via digital sensors (Table 2.2).
Table 2.2 Overview of various capturing techniques implemented in intraoral scanner systems
Laser Beam-based IOS Systems
Regarding data acquisition technology, laser beam-based IOS systems use either still image (e.g., E4D Dentist, iTero, 3D Progress) or continuous image (e.g., PlanScan) capturing techniques. These techniques enable the IOS to capture a series of images at various angles and positions. 3D rendering of the object in real time follows assembly of the captured images (Fig 2.3). Depending on the IOS system, the rendered 3D virtual models are either mono- or multichromatic. Although they still do not represent real shades, the so-called true color models facilitate the advantage of simply differentiating between hard and soft tissues. Another main characteristic of laser beam-based IOS systems is that there is no need to use a reflecting agent (except for the E4D Dentist, in cases of presence of a very translucent enamel on the cavosurface or of a metallic restoration on an adjacent tooth). The two main methods implemented in the laser beam-based IOS systems are the parallel confocal imaging technique and the laser triangulation imaging technique.
Fig 2.3 Rendered 3D data from an intraoral scanner (Zfx, Dachau, Germany).
Parallel Confocal Imaging Technique
The parallel confocal imaging technique is derived from the field of microscopy. In this imaging technique, parallel laser beams are sent through the IOS system’s scanning wand to hit the object that is to be scanned. The laser beams that hit the target at a specific focal length bounce off and return through a small pinhole, strike the laser sensor, and are subsequently converted to a digital image. A representative system implementing this technique is the iTero (Cadent, Carlstadt, NJ, USA). Around 100,000 parallel red laser light beams are projected by the scanner at 300 different focal depths spaced approximately 50 μm apart. This way, a field 14 mm × 18 mm is sampled within one-third of a second and the data is digitized afterwards.9,18 This spacing allows for an approximate scan depth of between 13 and 15 mm. In total, the system captures approximately 3.5 million data points for each arch being scanned.18 The successor of this system was introduced at the International Dental Show (IDS) 2015 and is called the iTero Element (Align Technology, San Jose, CA, USA). The new version of iTero retains the same working principle, while exhibiting enhanced acquisition capabilities, capturing 6,000 frames per second compared to the 800 frames per seconds by its predecessor.19 A similar technique is the confocal microscope recognition with Moiré effect, which is used by some IOS systems (e.g., Zfx/Organical Scan Oral/Cyrtina/3D Progress) (Fig 2.4).
Fig 2.4 A representative image of a confocal microscope (3D Progress, MHT, Verona, Italy/ Zfx, Dachau, Germany).
Laser Triangulation Imaging Technique
In this technique, the scanner utilizes a red laser beam and micromirrors that oscillate at 20,000 cycles per second to capture a series of still images from multiple angles around the object in order to generate a 3D model.4,9,20 This technology is similar to the triangulation technique implemented in laser beam-based IOS systems. However, the triangulation technique implemented in light beam-based IOS systems requires only a single orientation of the camera in order to be able to capture all the details of the target area from this single image.21,22 Representative IOS systems that utilize this technique are the E4D system (D4D Technologies LLC, Dallas, TX, USA) and PlanScan (Planmeca, Helsinki, Finland). However, the latter utilizes a blue laser rather than the red laser beam implemented by E4D.
Structured Light Imaging and Laser Triangulation Technique
A combination of the aforementioned imaging techniques facilitates continuous image capture to create an accurate 3D representation of the prepared teeth. This technology is currently implemented in the CS 3500 (Carestream Dental, Atlanta, GA, USA), which utilizes a green laser and four light emitting diodes (LEDs; UV, blue, green, and red) for the acquisition and the illumination of the object, respectively, while a complementary metal oxide semiconductor (CMOS) sensor receives the acquired data. According to the manufacturer, the scanner has a field of view of approximately 16 mm × 12 mm and a working depth of –1 mm to 15 mm. Although information about the capturing speed is not disclosed, the scanner is completely powder-free and enables full-arch scanning. The digital data acquired by the CS 3500 can be used to render a multicolored model.
Light Beam-based IOS Systems
This group of IOS systems employs visible light beam for image capture. Here, the image capture techniques can vary between still image, video capture, and real-time image capture. Although system dependent, the majority of IOS systems belonging to this group require the application of titanium dioxide as a reflecting agent.
Still Image Capture Technique
The still image capture technique utilizes a technology known as active triangulation, in which the intersection of three linear light beams is used to locate a given point in a 3D space.23 This concept has been used in a variety of industrial measuring devices. However, surfaces that disperse light irregularly do not reflect it evenly, and surfaces that are irregular, such as tooth surfaces, adversely affect the accuracy of the scan based on triangulation.24 Consequently, an opaque powder coating (titanium dioxide) is required to provide uniform light dispersion and to enhance the accuracy of the scan.25 The active triangulation techniques are implemented in the Cerec AC Bluecam system (Sirona Dental Systems, Bensheim, Germany). The contemporary versions of Cerec Bluecam utilize a blue light technology to scan the dentition.
Prior versions of Cerec utilized infrared light technology with a longer wavelength (820 nm) than the blue (470 nm) associated with the Cerec Bluecam. This development enables for an increased depth-of-field and is claimed to improve scanning accuracy by around 60%.20,22 The shutter speed of 17 ms per image further reduces the blurring risk, as does the option to rest the camera on the teeth (use of the Cerec camera support is recommended). The depth-of-field range itself, at 14 mm, is sufficient to allow operators to disregard this parameter entirely, because the image will always be accurately focused from cusp to preparation margin. The wavelength of the blue light also facilitates a nearly distortion-free representation, even close to the edges, of the image.22,26 MIA 3D (DynSys3D, Migdal Ha’Emeq, Israel) is another system that uses the active triangulation technique. Both systems capture and render a monochromatic 3D model.
As a further evolution of the Cerec Bluecam, Sirona launched the Cerec Omnicam. The new camera is able to capture images combining continuous and static stripe projection techniques. The main feature of this IOS system is that the teeth in most cases do not necessarily require prescan powdering. Furthermore, during the scan procedure the image data are reproduced, with natural color and in real time, on the screen, while a full-color 3D model is generated.27
Video Capture Technique
While all other technologies presented in light beam-based IOS systems use some form of still image acquisition, the active wavefront sampling (AWS) technology is the only technique which captures 3D data in a video sequence28 and models in real time.9 AWS refers to getting 3D information from a single lens imaging system by measuring depth based on the defocusing of the primary optical system.29 The technique is implemented in the Lava Chairside Oral Scanner (COS) and its successor, the True Definition Scanner (3M Espe, Seefeld, Germany).30,31 Lava COS incorporates 192 blue LEDs for illumination, three sensors, and 22 lenses that capture the object simultaneously from different perspectives.9,20 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.29 The system captures 20 3D data sets per second and each data set contains 10,000 data points of information, resulting in roughly 24 million data points (or 2,400 data sets) captured per arch.20 The operator has a field of view of approximately 10 mm × 13.5 mm in which data is being captured.9 Similar to the systems that use active triangulation, and due to the application of a reflecting agent, the rendered models are monochromatic. The successor system, True Definition Scanner, implements the same technology as Lava COS, but with fewer LEDs and lenses. The scanning wand of True Definition Scanner consists of six LEDs for illumination, three optical lenses, and a CMOS sensor for image capturing and data acquisition.
Ultrafast Optical Sectioning Technique
The ultrafast optical sectioning technology is similar to the video capture technique and facilitates continuous image capture. Rather than artificially forming interpolated surfaces, this technique utilizes up to 1,000 3D images to create true geometries based on real data. The technology is being implemented in the 3Shape TRIOS IOS system (3Shape, Copenhagen, Denmark). According to the manufacturer, the scanner captures over 3,000 two-dimensional (2D) images per second, which is 100 times faster than a conventional video camera.32 The TRIOS (3Shape/Cara) has a field of view of approximately 17 mm × 20 mm and a working depth of 0 to 18 mm. Additionally, it does not require the application of a reflecting agent, compared to other light beam-based IOS systems. The scanner is completely motion- and position-free and can be placed on the teeth for support during scanning. The software and hardware of TRIOS have the capability to capture and render a fully colored model (Fig 2.5). The evolution of the existing system led to the third generation of TRIOS, the TRIOS 3. The new IOS system integrates an intraoral camera for taking high-definition pictures, facilitating practitioner–patient communication. TRIOS 3 is also capable of matching and saving the teeth shades during a digital impression. A new version with a wireless scanning wand that facilitates a significant faster scanning capability was introduced at the 2017 IDS.
Fig 2.5 Rendered model in RealColor after scanning with Trios (3Shape, Copenhagen, Denmark).
IOS systems were developed to overcome the problems and disadvantages of the traditional impression fabrication process, particularly, mold instability, plaster pouring, laceration on margins, as well as geometrical and dimensional discrepancies between the die and the mold. Furthermore, IOS systems provide several advantages over conventional impressions. These include the elimination of the need for impression trays and materials, the immediate evaluation and quality control after the scan, and the digital archiving of patient records. On the other hand, studies have shown that the accuracy of IOS systems seems to be similar to that of conventional impression materials. The accuracy of a full-arch impression using conventional materials is approximately 55 µm, while that of IOS systems is between 40 and 49 µm.26,33,34 Furthermore, the accuracy of elastomeric impressions seems to be negatively affected by particular angulation of the axial walls of abutment teeth, while the IOSs can accurately reproduce a tooth abutment irrespectively of its geometry.35 Comparing the different steps necessary for the fabrication of a restoration, IOS systems seem to require fewer steps than the conventional impression techniques, being significantly faster than the conventional procedure.36-39 Particularly, an in vitro study found digital impression-making methods were significantly faster compared to the conventional technique, after contrasting them in three realistic clinical scenarios, such as impression making of one, two, and full-arch abutments for the fabrication of a crown, a three-unit fixed partial denture, and full-arch single crowns, respectively (Fig 2.6).36
Fig 2.6 Comparison between clinical and laboratory steps required for conventional impressions vs. IOS systems.
CAI does not eliminate the problems related to the isolation of subgingival margins. This is especially demanding in the esthetic zone, where the restoration margins have to be hidden. Here, it is obvious that IOS systems require even more preimpression isolation (e.g., placement of retraction cords) of prepared tooth than the conventional impression technique (Fig 2.7). Conventional impression materials have the ability to flow around the prepared tooth, below the margins into the sulcus, thereby providing a good marginal reading. On the other hand, to achieve an adequate digital impression, the preparation margins must be visible to the naked eye in order to be readable by the IOS system. Otherwise, the application of an intraoral scanner is limited when the gingival tissues cover a deep preparation and block the light beam emitted by the IOS system, preventing the acquisition of an ideal reading to be obtained (Fig 2.8). Clearly, IOS systems need to be improved in this area.13
Fig 2.7 Clinical procedure for CAI using the iTero IOS system.
Clinical Application of IOS Systems
Digital Impressions Using IOS
Despite their differences, all IOS systems operate under similar principles. For tooth restorations, the dual cord technique is recommended for CAI using IOS systems whenever subgingival preparations are present, so that a direct visualization can be achieved during the scanning procedure (Fig 2.8). After the intraoral positioning of the camera, the prepared, adjacent, and opposing teeth are scanned. Also, a bite registration must be digitally recorded after the patient is instructed to close into the maximal intercuspal position. Then, the data is processed by the software in order to render a 3D object that represents the scanned structures, which is then displayed on the screen.9,40 The following stage depends on the technology concept of the IOS system used. In-office systems are able to perform not only the digital impression (CAI), but also the design (CAD) of the restoration, manipulating the acquired data with the software provided by the same manufacturer. This process can be accomplished in the dental office exclusively or in the local dental laboratory. Then the digital data of the designed restoration is sent to the milling device of the dental office or the dental laboratory for final production. The majority of IOS systems are designated for CAI, and data must subsequently be uploaded to the manufacturer’s server for further processing. When the manufacturer receives the scan data, a cleaning process is performed to remove the artifacts. Also, a conversion of the data to a compatible file format can be carried out, depending on the system. Therefore, the manufacturers usually charge fees, usually called “data processing fees” or “click fees.” Then, the data is sent to the local lab or the design center where the CAD process takes place. Depending on the particular IOS, the downstream workflow can be categorized into three classes: closed, open, and closed–open systems.
Fig 2.8 A representative image of a clinical situation using conventional and digital impression techniques (from left to right). When using IOS, the need for soft tissue retraction around an abutment is of great importance, to allow the light beam emitted by the IOS system to read the preparation margins without limitations.
For closed systems, the same manufacturer provides the IOS, the CAD software, and the CAM device. With open systems, the clinician can choose the preferred CAD software and CAM process. In this case, the scan data must be converted into the Standard Tessellation Language (STL) file format. An STL file describes the surface geometry of a 3D object, ignoring other specifications (e.g., texture, color). This type of file format is universal and supported by most CAD software; however, is not read in the same way across CAD platforms. Therefore, exact information about the CAD operating system is required by the IOS manufacturer to accomplish software-compatible STL format conversion. After the data has been converted, it is sent back to the dental laboratory or the design center where the CAD process takes place and subsequent fabrication of the restoration takes place. For the closed–open systems, the workflow is similar to that of the open systems. However, the dentist or the lab technician requests the option of working with a CAD software package other than that provided by the IOS manufacturer, and the manufacturer converts the data to the STL file format; additional data processing fees are charged.
Implant Digital Impressions Using IOS
For implant-borne restorations, the digital workflow remains fundamentally similar to that for natural abutments. The main difference in such cases is that CAI requires the use of scan bodies. These are devices that can be screw-retained or snapped onto the implants prior to the scanning process and then be scanned by the IOS. They exhibit a specific geometrical surface morphology in order to be identified by the IOS software (Fig 2.9).
Fig 2.9 (a, b) BellaTek Encode Healing Abutment (Zimmer Biomet, Palm Beach Gardens, FL, USA). (c, d) Example of screw-retained scan bodies with different geometries.
The scan bodies allow the scanning device and subsequently the software to accurately determine the 3D position of the dental implant, as well as the associated hard and soft tissues in reference to this position. In other words, the scan bodies are considered as the successors of the traditional implant copings used in such impressions,41 minimizing the steps needed and the potential inaccuracies that can occur all along the conventional process.42 Although the principles of CAI relating to dental implants are similar, the workflow exhibits some differences among the various systems. These differences depend on both the IOS and scan body system.43 After performing the computer-aided impression with the scan body, the scan data must be sent to the manufacturer or to a laboratory equipped with suitable CAD software, where a virtual model with the accurate implant position is created through algorithm alignments. A virtual customized anatomical abutment is designed and can be fabricated. Combining the iTero intraoral scanner (Cadent) with Straumann scan bodies (Institut Straumann, Basel, Switzerland), physical polyurethane casts are milled, followed by assembly of the already designed and fabricated customized abutment and implant analog in the appropriate cast (Insititut Straumann). The cast with the customized abutment is then digitally scanned to enable fabrication of the final restoration.44 For cases in which True Definition Scanner (3M Espe) and BellaTek Encode scan bodies (BellaTek Encode, Zimmer Biomet, Palm Beach Gardens, FL, USA) collaborate, the scan data is simultaneously sent to 3M Espe and Zimmer Biomet. The definitive abutment is designed and milled by Zimmer Biomet, followed by the printing of stereolithographic (SL) models with respect to the final abutment form, by 3M Espe. The abutment and SL models are sent to the lab technician for fabrication of the restoration.43,45 Although this entire process can be accomplished digitally without the SL models, they can provide important information for individualized ceramic veneering.43 BellaTek scan bodies are actually coded healing abutments, which can also be acquired by means of a conventional impression.
An alternative technique has also been developed that exclusively utilizes scan bodies from Biomet 3i. Once stone casts are created and mounted in an articulator, they are sent to the manufacturer for scanning. An individualized anatomical abutment can then be designed via CAD and milled from a solid Ti or ZrO2 block via CAM.46,47 The implant analog is placed in the definitive cast by a specialized robotic device (Robocast Technology, Zimmer Biomet) and sent back to the dental lab for fabrication of the restoration. Using this type of scan body, a second implant-level impression is not necessary, and the need to remove the healing abutment upon delivery of the definitive restoration is also eliminated.42,45
In addition to the aforementioned techniques, the Cerec AC allows implant CAI either with the aid of a prefabricated abutment or a scan-compatible coping. In the first case, the clinician must modify and prepare a stock abutment and then follow the conventional chairside digital impression protocol. Once the crown design is performed using the Cerec AC software, the data is sent to the inLab MC XL (Sirona Dental Systems) for milling. In the second case, in which the use of a scan-compatible coping is planned, Sirona offers two options: the TiBase and ScanPost abutments combined with a proprietary scan body for a cemented or screw-retained final crown, respectively. In these cases and after the optical impression, the clinician sends the scan data to the laboratory, where the design and milling of the definitive superstructure will take place using the Cerec inLab. For screw-retained restorations, Sirona has launched specific monolithic lithium disilicate (LiSi2) blocks with a canal for the future screw access hole.43,48
The implant CAI can be performed without any special tissue management for restorations located in the posterior segments, where esthetics is not the most critical issue.49 In the esthetic zone, on the other hand, soft tissue management by means of a screw-retained provisional is of great importance for achieving an optimal emergence profile and an esthetic result. Two techniques have been described to optically capture the emergence profile. In the first, after the removal of the temporary abutment, a scan body is screwed onto the implant and a digital impression is taken, simultaneously capturing the implant position and the surrounding soft tissue together with the emergence profile.44 For the second option, the optical impression is taken in two steps: initially, the optimally shaped emergence profile is scanned; then, a second scan is performed while the scan-compatible impression coping is tried-in to determine the 3D position of the implant. Afterwards the scan data are matched and a proposal for the final abutment design is generated using CAD software.50
Regarding the accuracy of digital implant impressions, encouraging clinical results have emerged in terms of restoration with single implants.51 The accuracy of implant CAI can be affected by several factors, such as the degree of implant angulation,52-54 the distance between implants,55 and the implant level and depth.53,54,56
Moreover, implant CAI has been evaluated as a more time-efficient approach than the conventional impression method for single-implant rehabilitation by both in vitro and clinical studies.41,57,58
Implant Planning Using CAI
Alongside the development of CAI, the development of cone-beam computed tomography (CBCT) enabled the generation of accurate 3D representations of the osseous jaw anatomy. Several contemporary CAD/CAM systems can work well with CBCT, providing thorough diagnostic data which can be combined, thereby enhancing the implant planning process. The oral and dental surface data sets, as well as the radiographic details, are obtained by using IOS and CBCT systems, respectively. The combination of these data sets requires compatibility between the IOS software and the implant planning software package, in which the common data points are matched (Fig 2.10). Once the matching (superimposition) is completed, the dentist can plan the position of the implant depending on a virtual setup. Afterwards, a surgical guide is produced by the manufacturer and delivered to the clinician (Fig 2.11).48
Fig 2.10 Using an appropriate implant planning software, the imported 3D surface data from the IOS system (a) can be superimposed onto the 3D model of the jaw obtained by CBCT (b), thereby combining soft and hard tissue information onto the computer screen (c). The software shown here is Smop (Swissmeda, Zurich, Switzerland).
Fig 2.11 Consequently, a virtual set-up of the missing tooth can be performed and the implant position can be precisely planned. Accordingly, the software proposes a design of the surgical guide.
Cast Fabrication
Although not provided in all systems, the fabrication of casts based on data acquired by IOS systems is possible. Depending on the IOS system used, two techniques are used for cast fabrication: the additive and the subtractive techniques. For the additive technique, stereolithography (SL) or 3D printing are currently the methods of choice, by which the casts are fabricated by photopolymerized liquid resins, the layers of which are sequentially added and photopolymerized via UV light or visual light. The subtractive technique uses plastic- or resin-based materials in solid form, which are milled by a computer numerical-controlled multiaxis milling machine (Fig 2.12). The constructed casts can be used either in conventional fabrication of restorations or as a communication tool between the dentist, the patient, and the lab technician. To date, there are few studies available regarding the accuracy of digitally fabricated casts. The subtractive technique shows acceptable accuracy, while the SL technology demonstrates greater accuracy for cast fabrication.59,60 Additionally, it seems that the accuracy is variable across systems.60
Fig 2.12 Casts produced using CAI data from different IOS systems. From left to right: (a) Cerec AC Bluecam (additive manufacturing; stereolithography); (b) iTero (subtractive); and (c) Lava COS (additive).
Implant Capturing Technology Via Photogrammetry
While the digital workflow for the use of IOS systems for CAI of partially edentulous jaws is well established, the use of such systems for edentulous jaws that have received implants remains a difficult task. This is mainly due to the lack of anatomical landmarks to facilitate accurate impressions as well as the lack of knowledge about the accuracy of IOS systems for edentulous jaws with/without implants. In order to solve this issue, the use of photogrammetry to capture the implant positions is proposed. Photogrammetry technology is already in use in the automotive and aerospace industries for quality control of mechanical parts that require very high precision in their manufacture. A representative system of this technique is PIC (PIC dental, Madrid, Spain). The system is comprised of two CCD cameras (PIC camera, PIC dental) (Fig 2.13), which are designed to accurately determine the position of the implants by means of the identification of flag-shaped abutments screwed onto implants with unique individual coding (PIC abutment, PIC dental; see Figs 2.14 and 2.15). The camera has an infrared flash that constantly illuminates the scanned object while eliminating the shadows that occur with ambient light. The PIC camera captures 50 3D photographs for every two PIC abutments. To do this, it automatically takes 10 extraoral pictures per second with an error of less than 10 microns. The registered angles and distances between implants are interrelated and treated as a unit (Fig 2.16). System software calculates average angles and distances between implants from these photographs, obtaining an accurate relative position of each implant in vector format. The resultant PIC file (PIC dental) contains all the information about implant positions, geometries, connections, healing abutments, and screws that are later required by CAD/CAM software. After capturing of implants, soft tissue registration takes place. This procedure can be carried out using an IOS device or a desktop scanner. The software matches the acquired data of the PIC file and STL of soft tissue registration, yielding a file that contains both implant and soft tissue information. After registration of the opposing arch and maxillomandibular relationship, the data can then be imported into any CAD software to design a future restoration.
Fig 2.13 PIC camera for implant position capture via photogrammetry. The capturing device is equipped with two CCD cameras. Illumination of the scan abutments is performed by infrared flashes surrounding the lenses.
Fig 2.14 Flag-shaped PIC abutments, which are screw-retained onto the implants for the capturing procedure. Each abutment is uniquely dot-coded to allow easy identification of each implant.
Fig 2.15 Clinical example demonstrating the positioning of PIC abutments onto different implants. The PIC camera captures the 3D positions and angulations of implants and via the coded abutments.
Fig 2.16 The PIC software processes information about the angles and distances between implants. The data is then interrelated and treated as a unit to create a PIC file. Further steps include soft issue registration (e.g., IOS scan) and matching with the PIC file.
Based on clinical experience, the photogrammetry technique seems to provide reliable, fast, and comfortable digital acquisition of implant information. While the manufacturer claims an error range of less than 10 microns with the technology, studies about the accuracy of the data acquired from different clinical scenarios are still lacking.
Current Indications and Future Possibilities of IOS Systems
While the first generation of IOS systems was only indicated for the fabrication of inlays, contemporary IOS systems offer the possibility to fabricate a wide spectrum of fixed restorations, including inlays, onlays, veneers, single crowns, and fixed partial dentures (FPDs) (Table 2.3). Due to the current software and hardware configurations, the number of fixed partial denture units varies from one IOS system to the next. Depending on the system, the options of restorative materials can also vary from resins, nonprecious/precious metal alloys, and ceramics, to high-strength ceramics. The fabrication process can be either subtractive (milling or grinding) or additive (stereolithography, 3D printing, selective laser sintering, and so on). For the fabrication of high-strength ceramic restorations, subtractive procedures are the currently available manufacturing techniques. On the other hand, a limited number of IOS systems, including related CAD/CAM techniques, claim that they have expanded the indications from the fabrication of fixed restorations to removable partial dentures or even complete dentures (e.g., Omnicam and True Definition Scanner; see Table 2.4). Other systems can provide the possibility of implementing CAI for the production of implant surgical splints (e.g., 3Shape TRIOS). Regarding implant restorations, the majority of IOS systems support such an option with the help of scan bodies. The number and type of implant restorations are completely software dependent. The same concept follows the 3Shape TRIOS Scan IOS system to fabricate post-and-core restorations, via optical capturing of scanning flacks (3Shape Scan Post, 3Shape), which are provided in different lengths and diameters (Fig 2.17). Finally, some IOS systems, such as 3Shape TRIOS and iTero, extend their indication range to orthodontics, allowing not only the digitization of the procedure through the fabrication of an orthodontic appliance, but also digital analysis of the pretreatment situation and the treatment planning.
Table 2.3 Overview of different features and indications of commercially available intraoral scanner systems (information provided by the manufacturer may vary depending of device/software version and service strategy of manufacturer)
Table 2.4 Guide to available intraoral scanners with links to manufacturers (modified from Jokstad17)
| Product name | Manufacturer | URL |
| 3D Progress Plus | MHT (Medical High Technologies, Italy/Switzerland) | https://www.mht.it |
| Aadva ← IOS Bluescan-I ← a.tron 3D | GC, Belgium 2016 a.tron 3D, Klagenfurt, Austria | https://www.gceurope.com |
| Cerec OmniCam/BlueCam | Dentsply Sirona, Germany | https://www.dentsplysirona.com |
| Condor | Clon3D, Belgium | https://condorscan.com |
| CS3500/CS3600 | Carestream Dental, USA | https://www.carestreamdental.com |
| Dentium Rainbow iOS | Dentium, Korea | http://dentium.com |
| DWIO ← Diglmprint Steinbichler | Dental Wings, Canada ← 2013 Steinbichler | http://www.dentalwings.com |
| IntraScan Zfx | zfx, Germany | http://www.zfx-dental.com |
| i/s/can oral | Goldquadrat, Germany | http://goldquadrat.de |
| Itero Element/Itero | Align Technology, USA ← 2011 Cadent, Israel | http://www.itero.com |
| MIA3D | Densys, Israel | https://densys3d.com |
| Organical Scan Oral | R+K CAD/CAM Technologie, Germany | http://www.organical-cadcam.com |
| PlanScan ← E4D | PlanMeca, Finland ← 2015 E4D Tech, USA | http://www.planmeca.com |
| Primescan | Dentsply Sirona, Germany | https://www.dentsplysirona.com |
| Progress IODIS | Clon 3D / IODIS / Intellidenta (USA?) | https://clon3d.com |
| TRIOS 3 / TRIOS Color / Standard | 3Shape, Denmark | https://www.3shape.com |
| True Definition Scanner ← Lava COS (Chairside Oral Scanner) | 3M Espe, USA ← 2006 Brontes Technology | https://www.3mespe.com |
Fig 2.17 The 3Shape Scan Post system is approved for both intraoral application in the clinic and for model scanning in the laboratory; courtesy of Nelson Silva, Rodrigo Albuquerque, Luis Morgan, UFMG, Belo Horizonte, Bazil.
In summary, the current possibilities of IOS systems and their relatively wide indication spectrum, as well as software compatibility (open STL format), are gaining widespread acceptance in the dental community.
Hence, the current IOS systems can still be considered as a blueprint for future systems. Current research focuses on the extension of the indication range of IOS systems to include edentulous jaws. Once established, the fabrication of removable partial dentures, including complete dentures, would be possible using IOS systems. More interesting, the introduction of advanced imaging technologies such as optical coherence tomography (OCT) that are being used in other medical specialties (e.g., cardiology, ophthalmology, and dermatology) will facilitate the possibility for IOS systems to perform transgingival scans. In other words, this technology will allow CAI to be performed without placing retraction cords.61,62 A further technology that is still under development implements high-frequency ultrasound for intraoral scans (WhiteSonic, Mannheim, Germany). The manufacturer claims improved signal processing compared to existing IOS systems. Model-based concepts combined with powerful and intelligent algorithms make it possible to scan subgingival structures, such as preparation margins and bone. With such innovations, CAI will rapidly replace conventional techniques.
Miha Brezavšček, Dr Med Dent/Wael Att DDS, Dr Med Dent, PhD
A 70-year-old woman presented at the Department of Prosthodontics, University Hospital of Freiburg, Germany. Her chief complaint was the unattractive appearance of the upper front teeth, due to defective veneering material and discoloration (Fig 2.18). Because of the unesthetic appearance of the anterior teeth, the patient avoided showing her teeth while talking and smiling. Her wish was to renew all of the 20-year-old dental restorations in order gain a beautiful and harmonious smile (Fig 2.18). The patient’s medical history revealed a noncontributory general condition and the patient was not under any treatment or medications.
Fig 2.18 A photo of the patient’s smile showing intraoral anterior and occlusal views of the old prosthetic rehabilitation.
A comprehensive examination revealed multiple insufficient restorations, secondary caries, and insufficient composite fillings (Fig 2.18). The periodontal assessment depicted localized gingival inflammation. Functional examination revealed a stable occlusal scheme with canine-anterior-protected guidance during lateral and protrusive movements. The radiographic examination showed insufficient root canal fillings on teeth 45, 35, 25, 11, and an apical external resorption of tooth 11. The esthetic appearance of the existing fixed rehabilitation was deemed insufficient. All teeth were given a fair prognosis, except for teeth 25, 35, and 45, which were rated questionable, and tooth 21, which was deemed hopeless.
The final treatment plan comprised zirconia-based tooth-supported single crowns and FPDs in the maxilla and mandible.
Preprosthetic Phase
Following a professional dental cleaning, alginate impressions (Alginat Super, Pluradent, Offenbach, Germany) were made. A full diagnostic wax-up was performed in order to evaluate the feasibility of the final esthetic and functional outcomes. To evaluate the esthetic and phonetic parameters, the wax-up was tried-in clinically via a direct mock-up (Fig 2.19). Then, the old crowns and FPDs in the maxilla and mandible were removed. Direct provisional restorations (Luxatemp, DMG, Hamburg, Germany) were fabricated via silicone keys from the wax-up and delivered using a provisional cement (TempBond NE, Kerr, Orange, CA, USA) (Fig 2.20). During the preprosthetic phase, tooth 21 was extracted because of external resorption and tooth 35 due to secondary caries. Teeth 25 and 45 were extracted after removal of the existing posts and cores, which revealed an extensive loss of the tooth structure. In addition, all insufficient fillings were replaced and a direct post-and-core buildup of tooth 13 was performed. Soft tissue enhancement via a connective tissue graft was performed in tooth 21. The shade of the mandibular anterior teeth was improved through external bleaching.
Fig 2.19 A diagnostic wax-up was created to verify the predictability of the prosthetic rehabilitation. Esthetic and phonetic parameters were then evaluated via a mock-up try-in.
Fig 2.20 An intraoral frontal view of the inserted provisionals (a). Side views of the patient’s smile after the delivery of the provisional restorations (b, c).
A re-evaluation of the preprosthetic phase followed after 4 months. The patient exhibited a stable periodontal status with probing depths ranging from 2 to 3 mm with no bleeding. The extraction sites healed successfully without any complications. The successful outcome of the preprosthetic phase allowed for the execution of the prosthodontic treatment plan.
Prosthetic Phase
After the definitive preparation of maxillary and mandibular teeth, retraction cords (Ultrapak #000 Retraction Cord, Ultradent, South Jordan, UT, USA) were placed (Fig 2.21). The final impression was performed digitally with the help of an iTero intraoral scanner (iTero, Align Technology) (Figs 2.21d, e). This scanner uses powder-free technology and produces images via parallel confocal microscopy (details about the scan technology can be found earlier in this chapter).
Fig 2.21 Intraoral frontal and occlusal views of the prepared abutment teeth (a, b, c). The scanning procedure in the maxilla and mandible (d, e).
The scanning procedure began with the creation of the patient profile in the software interface. The digital impression was conducted first in the maxilla, starting with the most posterior tooth, and moving forwards through the whole arch. Scanning of each abutment tooth began at the occlusal surface, followed by the buccal surface and ending at the oral surface. The same scanning technique was also applied in the mandible. After taking the digital impression, a registration of the occlusal relationship was performed by scanning the three different areas of the arch (right, left, and anterior teeth). In order to assure a proper interocclusal relationship, the provisional restorations were used interchangeably in nonscanned areas as a bite reference during the scanning procedure (Fig 2.22).
Fig 2.22 Interocclusal relationship of the scanned images.
The obtained data sets were uploaded via a secure internet connection to the company server (Align Technology), where the initial digital file was cleaned and processed by the company computer software (Fig 2.23). Afterwards the data sets were converted into STL data format and sent together with the CAD/CAM-fabricated polyurethane casts to the dental laboratory for restoration design (Fig 2.23). By using CAD software (SimedaCad 2.0, Simeda Medical, Luxemburg), the STL files were imported and the restorations were digitally designed in their full anatomical form (Fig 2.24). Before performing the necessary cutback for the fabrication of the final zirconia framework, a prototype made of composite was milled and tried intraorally (Fig 2.24). Corrections of tooth length and form were performed either by adding flowable composite or by bur reshaping of the prototype. The modified prototype was scanned again with a laboratory scanner (3Shape) and the obtained data were matched with the previous restoration design, in order to assure an exact transfer of the performed corrections. Subsequently, anatomically shaped frameworks were designed using a digital cut back and milled from a zirconia block (SinaZ, Simeda Medical) (Fig 2.25a). An intraoral try-in followed, showing proper fit and retention of the zirconia frameworks (Fig 2.25b). At the same appointment, a spectrophotometer (Crystaleye, Olympus, Tokyo, Japan) was utilized to determine the appropriate tooth shade (Fig 2.25c). The veneering of the zirconia frameworks was performed with feldspathic ceramic (HeraCeram Zirkonia, Heraus, Hanau, Germany). Before finalization of the restorations, a biscuit try-in was conducted to evaluate the occlusion, esthetics, and phonetics (Fig 2.26). As the result was rated satisfactory by both the patient and the clinician, the restorations were finalized.
Fig 2.23 Digital images of the scanned maxilla and mandible. The optical impressions were processed by the company to portray the preparation margins. Polyurethane casts were fabricated by using digital data sets from the scanning procedure.
Fig 2.24 The SimedaCad 2.0 software was used to design the restorations. A prototype of the restorations was fabricated and tried intraorally.
Fig 2.25 By using a digital cutback, the framework design was created. The intraoral try-in of the zirconia frameworks showed proper fit and retention. The selection of the tooth shade was performed using a spectrophotometer.
Fig 2.26 Before finalization of the restorations, a biscuit try-in was performed to check esthetics, phonetics, and occlusion.
Before cementation of the final restorations, a radiographic examination and re-evaluation of the intraoral status were performed to check the vitality and the periodontal status of the abutment teeth. Furthermore, the inner zirconia surface of the final crowns was airborne-particle abraded with alumina oxide under a pressure of 0.5 bars and chemically treated with a monophosphate monomer (Clearfil Ceramic Primer, Kuraray Dental, Tokyo, Japan). Afterwards the crowns and FPDs were cemented with a dual curing adhesive cement (Panavia 21, Kuraray Dental; Figs 2.27–2.29).
Fig 2.27 Frontal view of the final crowns after cementation.
Fig 2.28 Lateral and occlusal views of the cemented restorations.
Fig 2.29 Frontal lateral views of the patient’s smile showing a successful esthetic outcome of the prosthetic rehabilitation.
One week after the insertion, the final re-evaluation of the occlusal relationship was conducted. The patient was enrolled in a 6-month recall regimen.
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