Computer‐Aided Design (CAD)
Jun Ho Kim, Alan J.M. Costa, José Lincoln de Queirós Jr, Juliana No‐ Cortes, Danielle A. Nishimura, Shumei Murakami, Reinaldo Abdala‐Junior, Daniel Machado, Claudio Costa, Otavio H. Pinhata‐Baptista, Shaban M. Burgoa, Andrea Son, Lucas R. Pinheiro, Danilo M. Bianchi, Allan R. Alcantara, and Arthur R.G. Cortes
2.1 Digital Imaging Methods
2.1.1 Cone Beam Computed Tomography
Cone beam computed tomography (CBCT) is a technique that allows for three‐dimensional (3D) observation of structures related to the maxillofacial area. CBCT uses a round or rectangular cone‐shaped x‐ray beam with a two‐dimensional x‐ray sensor to scan, performing 180–360° rotations around the head of the patient (Figure 2.1). During the scan, a series of projections is acquired, providing the raw data for volumetric reconstruction (3D). Multiplanar reformatting (MPR) of the primary 3D reconstruction allows studies of any selected plane in 2D or 3D views . The CBCT image is a matrix composed of small cubic units called voxels (volume element, the 3D version of a pixel, described in the previous chapter). Similar to pixel values, each number assigned to a voxel represents the linear x‐ray attenuation coefficient of the inside structure with a specific level of gray and numerical value (voxel value) .
18.104.22.168 Basic Knowledge
In recent decades, CBCT devices have been used in dentistry much more frequently than medical computed tomography (CT). The latter is an expensive device usually found in hospital settings. Medical CT devices can have single or multiple detectors that use a collimated, fan‐shaped x‐ray beam moving in a 360° circle within the detector ring (known as the “gantry”). The CT image is recorded and displayed as a matrix of individual 3D blocks that are the voxels. Similar to CBCT, multiplanar CT imaging acquired from axial scans (2D) may be reformatted by interpolation to render a 3D image .
When compared to medical CT, CBCT has advantages such as lower radiation dose, faster imaging, and higher spatial resolution of bone . Modern CBCT devices can offer lower fields of view (FOV), which means that only the region of clinical interest is scanned, resulting in even lower radiation doses. The use of CBCT is well established in implant planning for the evaluation of bone thickness, height, density (estimated using pixel values), and volume [4–6], and others as endodontics , periodontology , orthodontics , oral and maxillofacial surgery , and temporomandibular disorders .
Images from MPR are usually available in three different orthogonal planes – axial, sagittal, and coronal – to be used in diagnosis and treatment planning. However, it is also possible to obtain curved images by using the axial scan to draw a curve following the shape of the dental arch. These images usually show coronal panoramic reconstructions and a set of transaxial/parasagittal images representing cross‐sections of the alveolar ridge (Figure 2.2). These cross‐sectional images are commonly used for implant planning.
Another option is to use the raw CBCT axial images to render 3D reconstructed models to analyze the spatial disposition (angle, length, and diameter) of implants, screws, surgical or endodontic guides, prosthetic compounds, and orthodontic components. The raw data from CBCT or CT must be obtained in the DICOM® (Digital Imaging and Communication in Medicine) extension (described in the previous chapter) (Figure 2.3) to be read in the software and later exported as a 3D image in the Standard Tessellation Language (STL) extension.
22.214.171.124 Step‐by‐Step Procedure
- Prior to the examination, the patient should be asked to remove any metal objects, such as eyeglasses and jewelry. Removable prostheses should also be removed in most cases.
- Radiation protection measures (e.g., lead aprons, etc., as established by local regulations).
- Patients should always be positioned properly in the CBCT device (Figure 2.4). It is suggested that the best position for image quality of the sinuses, mandible, and maxilla is the prone position, rather than supine and oblique positions . The patient’s face needs to be aligned in the scanner with the head positioned between the x‐ray source and the sensor. This position should then be further adjusted to ensure the disposition of the desired anatomical structures within the limits of the selected FOV. Such adjustment is generally conducted with the aid of chin and head supports, and with a laser alignment beam that projects an illuminated line onto the face of the patient.
- Explain the procedure and ask the patient to swallow and avoid moving during the scan. (For image‐guided surgeries, it is important for the patient to use lip retractors in occlusion during the scan, as further explained in Chapter 6.)
- Define the imaging parameters and the FOV to be scanned on the scout image (Figure 2.5).
- Initiate the scan following the manufacturer’s instructions.
- Save the scan in the DICOM format (a folder with one file per axial slice will be created), which can be opened using a DICOM viewer for diagnosis (Figures 2.2 and 2.3) or a CAD software dedicated for dental treatment planning (further discussed in the following chapters).
2.1.2 Intraoral Scanner
126.96.36.199 Basic Knowledge
The conventional workflow using trays and impression materials has been improved for many decades. However, a previous study found that about 50% of the impressions sent to a laboratory result in inadequate or inaccurate models. This can occur because, until the end of the service, many materials are used, each one with its particular work technique. Careful analysis is required at each stage of the process, as any failure will not be corrected by the next stage, thus compromising the final result of this flow.
Currently, digital impressions, by the use of intraoral scanning, can generate an STL file, which represents the first step of the digital path, in which the clinical situation can be fully moved to a virtual environment. However, when necessary, physical molds can still be manufactured from the same STL files using rapid prototyping technologies.
Regarding patient‐based outcomes, digital impression leads to less patient anxiety, is more comfortable, causes less nausea and allows the patient to observe the area of interest on the computer display. From the point of view of process agility compared to the entire process from molding to patient rehabilitation, digital flow, with intraoral scanning, reduces process steps and promotes fast communication with the laboratory.
Using intraoral scanning ensures immediate determination of print quality; virtual 3D models of patients are obtained, which can be saved to the computer without the need for a physical model. This economizes on time and space and provides the ability to easily send models to the lab using email, reducing time and costs. The clinician can save money on purchasing impression materials and manufacturing plaster models; it is possible to store virtual models of patients without having to dedicate a space inside the clinic to them. Not least, the clinician can have a powerful marketing tool for more effective communication with the patient.
Intraoral scanning technology has been developed very fast. Currently, there are more than 10 different intraoral scanners on the market and companies are developing devices and methodologies from more than eight countries.
- TRIOS® 4 (Figure 2.6) – 3Shape A/S (Denmark).
- CEREC® Omnicam (Figure 2.7) and Primescan – Dentsply Sirona (USA).
- CS 3700® – Carestream (USA).
- 3D Progress – MHT SpA (Italy) and MHT Optic Research AG (Switzerland).
- iTero – Align Technologies (USA).
- Bluescan®‐I – A•TRON3D® GmbH (Austria).
- DPI‐3D – Dimensional Photonics International, Inc. (USA).
- E4D – D4D Technologies, LLC (USA).
- IOS FastScan – IOS Technologies, Inc. (USA).
- Lava™C.O.S. – 3M ESPE (USA).
- MIA3d™ – Densys 3D Ltd. (Israel).
- DirectScan – HINT – ELS GmbH (Germany).
- Panda P2® – Pingtum Technologies (China).
- Medit i700® – Medit Corp (South Korea).
- Vectra 3D – Canfield Scientific (USA).
The intraoral scanner is a medical device consisting of a handheld camera (hardware), a computer, and software. Its purpose is to accurately capture the 3D geometry of an object.
The most widely used format of the 3D digital file extension of images captured by the intraoral scanner is STL. Among the main technologies for scanning an object are triangulation, confocal, AWS (active wavefront sampling), and stereophotogrammetry.
Triangulation is based on the principle that the position of a point on a triangle can be calculated, provided that two points of view have known positions and angles. Examples of intraoral scanners using triangulation technology are Cerec Omnicam (Dentsply Sirona), IOS FastScan (IOS Technologies, Inc.), Medit i700 (Medit Corp), and MIA3d (Densys 3D Ltd).
Confocal imaging is based on acquisition of both focused and nonfocused images from different depths. This technology enables detection of image sharpness to infer distances in relation to the object, according to the focal length of the lens. The level of sharpness obtained in the scan is directly proportional to the dexterity of the operator. Examples of confocal intraoral scanners are TRIOS 3 and TRIOS 4 (3Shape), iTero Element2 and Element5D (Align Technologies), and 3D Progress (MHT SpA).
Active Wavefront Sampling (AWS)
The AWS technique enables the capture of a surface image using a camera and an aperture off the optical axis of a module that rotates around this axis. Distance and depth information can be derived and calculated from the outcome of each point. An example of an AWS intraoral scanner is the Lava C.O.S. (3M ESPE).
Stereophotogrammetry estimates all coordinates (x, y, z) solely by using an image analysis algorithm. As this approach relies on passive light projection and software rather than active projection and hardware, the camera is relatively small and easier to handle, and it is less expensive to produce the images. An example of a stereophotogrammetric device is the Vectra 3D (Canfield Scientific).
Clinical differences have been reported among IOS devices employing the same technology. These differences are usually related to the time it takes operators to become familiar with the ergonomics and usability of the software for each intraoral scanner. It is noteworthy that the learning curve of intraoral scanning may be initially slow.
Dental tissues have several reflective surfaces, such as enamel crystals or polished surfaces. These surfaces could prevent the software from capturing a point of interest due to overexposure. To avoid this, professionals could slightly change the camera’s orientation or employ systems that use cameras with a polarizing filter.
Scanning strategies refer to the order of intraoral scanner movements in relation to the dental arch to increase the quality and accuracy of the virtual model. Recent studies have shown the impact of the scan path on the accuracy of the resulting 3D models. During scanning, a regular and continuous movement should be maintained, ideally with a constant distance and centered in relation to the object. The main general steps for intraoral scanning are summarized below.
188.8.131.52 Step‐by‐Step Procedures
The following step‐by‐step procedure is described using a TRIOS 3 (3Shape) device. Most of the steps, however, are similar for most of the other systems and manufacturers.
- Connect the intraoral scanner to the computer with the specific software of the equipment to be used, which has a valid license key (for scanners attached to a cart, it will already be connected to the dedicated computer).
- Connect the equipment to power and turn it on.
- On the desktop screen, double click on the icon for the scanner software.
- On the initial screen of the intraoral scanner software (Figure 2.8), choose “new patient” to register an unregistered patient, or “new case” to perform a new scan on an already registered patient.
- Choose the laboratory (or email address) to which to send (export) the scan when it finishes.
- Define in the options that the software offers the type of restoration to be performed (scan only, implant planning, anatomy, abutment, bridge, etc.).
- Click on the “next” icon to proceed to the scan.
- Follow the steps indicated in the specific workflow bar that appears on the software’s scan screen.
- Scan both maxillary and mandibular dental arches, always following a scanning protocol (Figure 2.9) and avoiding repeat scanning of the same regions (Figure 2.10). In addition, perform the digital bite registration.
- Correct any failures in the mesh as indicated by the software. After scanning both dental arches and bite registration, proceed with the other complementary scans (dental preparations, scan bodies, etc.), as well as recording the occlusion scan.
- Once the scans are finished, carry out the mesh postprocessing (Figure 2.11) by using software tools (some systems perform part of this process automatically).
- With the postprocessing done, we are ready to export the scans (Figure 2.12).
- It is possible to export or directly send the scan files to a laboratory or client using the specific tools of each software. All files could also be downloaded into folders on the computer hard disk or to temporary storage devices (memory cards or external hard disks).
- Choose the type of file extension of the scan to be exported (some software programs work only with STL files; others additionally allow for exporting polygon file format [PLY] or OBJ files).
Intraoral Scanning of Edentulous Patients
The scanning technique mostly recommended for the edentulous ridge is the “zigzag” scanning strategy. This technique helps to maintain the continuity of the images following the palatal vestibule direction, always starting from the left side toward the right side, or vice versa without interruption and complementation of the palate region during capture. Conventionally, most professionals who choose to scan the toothless arch use the file to make an individual tray that can be produced manually on printed work models or directly by additive manufacturing in special resins, after drawings made in the software. The individual tray would be able to capture the areas that might not have been captured by the intraoral scanner. Compared to the maxilla, the mandible usually presents greater difficulty when obtaining the scan due to the presence of a mucosa with greater mobility.
The recommended scanning technique that will ensure greater accuracy of results performed in a fully digital workflow, based on publications that used TRIOS scanners [13, 14], and related scientific evidence, follows the sequence below.
- Prior selection of a U‐shaped lip retractor with adequate dimensions for the patient and capable of retracting and stabilizing the oral tissues while avoiding overextension. The clinician should ideally have an assistant for the proper use of the retractor and possible saliva aspiration if necessary. A fluid, radiopaque resin that adheres to the mucosa can be applied in the form of small spheres (1–2 mm) in areas without mobility at different points in the arch to increase surface characterization, facilitating scanning, if necessary. These tags can be removed later in planning software, or in the scanner’s own software after scanning is complete.
For the maxilla (Figure 2.13), the recommended scanning path has the following sequence: selection of one side of the arch in the tuberosity region through the occlusal view, heading toward the opposite side of the arch. Then, migrate the position of the scanner to the middle of the arch in the anterior portion, from there completing the entire palatal area, traversing the region from one side to the other. The scanner must complete the scan in a fluid and uniform way, ensuring the union of the scanned areas. The following steps need greater care as the scanner can be lost due to the presence of brakes and bridles. Therefore, the scanner must be positioned in the posterior region, starting again in the tuberosity region, but capturing the vestibular region. To complete the other side, the scanner must be paused and positioned in the posterior region, capturing similarly to the previously finished side. It is recommended that the scanner be tilted slightly so that it can capture the transition from the occlusal to the vestibular mucosa. With practice, the user will be able to perform the scan continuously without interruption of the scanner, preventing any image overlapping.
For the mandible, the recommended scanning path has the following sequence: selection of one side of the arch in the retromolar region with the scanner tilted slightly to the lingual, frequent capture until the retromolar region on the opposite side, followed by inclination of the scanner to the vestibular region, ending the scan following the entire vestibular to the opposite side, taking care that the scanner is positioned so that it can capture the occlusal and vestibular area, ensuring image union. If the patient has the ridge resorbed, it is recommended that the strategy be segmented by capturing first on one side and then on the other. Thus, the scanning would start in the retromolar region on one side until the middle of the arch, proceeding to the vestibular region on the same side, ending again in the retromolar region. From there, the scanner would be positioned again in the middle of the arch, proceeding to the lingual region of the missing side and ending by the buccal region on the same side to the retromolar region. During the break, excess saliva could be removed and the patient could rest for a while until scanning resumes.
To perform the bite registration and capture the VOD (vertical occlusal dimension), an interocclusal device adapted to the maxilla and mandible can be made with materials such as light and heavy silicone so that it is fully adapted to the ridge and allows for ideal positioning of the mandible for the patient occlusion. This device can be scanned using the intraoral or extraoral (desktop) scanner and later the file can be used by the planning software for alignment of the maxilla and mandible scans using the best‐fit algorithm that seeks the best possible alignment from records from similar areas. An adaptation of this technique would be the application of cutouts in this record, enabling the visualization of the patient’s edge and scanning the record in the mouth. For the occlusal registration, the scanner normally searches for similar information, finally generating the alignment of the identified meshes. The technique is easier to perform when the patient has tooth remnants or an existing prosthesis; otherwise, the ideal would be for the patient to have prefabricated evidence bases to facilitate occlusal registration.
- After the scan is finished, the files are postprocessed and inspected to verify the need for possible corrections and then exported for use in planning software.
An alternative to intraoral scanning, but using the same equipment, would be to scan the base of the patient’s relined prosthesis. Current software allows the scanned meshes to be inverted, allowing for later use within the normal workflow.
For the planning and production of the prosthesis to be made, the clinician can choose to use the CAD‐CAM system present in the clinic or send the records to a laboratory. The next steps would cover generating an individual tray, base plate, recording of vertical dimension, occlusal plane, lip support, length of maxillary central incisors and midline adapted to the patient. The next step is assembly in an articulator with information on face bow and mandibular relationship, assembly of teeth and extension of the prosthesis. Depending on the user’s expertise, most steps can be reduced and simulated directly within the planning software according to the records made due to the possibility of overlapping several files from the same patient.
Scans of edentulous patients are also used for planning guided surgery, in addition to making removable prostheses, serving as a basis for the production design of immediate surgical and temporary guides.
Additional scans such as bite occlusal registration and facial scans can be performed using different devices to provide greater predictability of results. Another benefit of using digital tools is the possibility of producing different prototypes at different stages, allowing for greater certainly prior to the production of the definitive prosthesis. Currently, definitive prostheses can be made by either subtractive manufacturing or additive manufacturing. In this context, milling complete dentures is still the best option.
The techniques described require further clinical validation, as the lack of differentiation of the scanned surface presents scanning difficulties. The use of the retractor is an excellent solution covered in the most recent articles, but incorrect use can cause overextension that causes lack of retention of the total denture. However, several studies have reported numerous problems caused by the conventional molding method, such as the presence of bubbles or holes and distortions related to the plaster model. With the increase in use of scanning technology, we will likely see a continuous advance in both clinical and laboratory expertise, presenting advances and improvements in the quality of files obtained and work carried out.
2.1.3 Desktop Scanner
184.108.40.206 Basic Knowledge
The use of digital technology is currently an essential part of many aspects of life, in food manufacturing, social interactions, entertainment, and especially in health [15, 16]. Revolutionary changes in dentistry were only possible with advances in digital technologies, such as the use of photographs, digital radiographs, CT, and mainly by the computer‐aided use of scanners associated with computer‐aided design and computer‐aided manufacturing (CAD‐CAM) . The first commercially available system used for intraoral scanning dates back to 1987; known as the CERC system, it basically worked on light triangulation principles and required an opaque powder coating.
The introduction of digital technology has increased the options available for dental treatment. Clinicians have been using plaster models as the main tool for diagnosis and fabrication of restorations, prostheses, planning and communications, but these models have disadvantages such as fractures, degradation, and loss of surface structure, and require substantial storage space [18, 19]. The study models allow the clinician to obtain a copy of the morphology and spatial relationships of the teeth, but this information may be incorrect due to the molding process , which depends on the operator, and material failure can occur. For example, after preparing a dental element for making a single prosthesis in the conventional method, several steps are necessary before production of the final restoration, with possible errors such as choice of appropriate material, molding technique, disinfection protocol, transport, type of plaster and even the time between individual steps influencing the accuracy and final result .
The introduction of the CAD‐CAM system in dentistry resulted in a more accurate fabrication of prosthetic structures and greater accuracy of dental restorations, and this technology has been improving since 1980. The automation and optimization of this process increase the quality of restorations through the use of new biocompatible materials, particularly high‐performance ceramics such as zirconia and lithium disilicate.
The fully digital workflow is not yet a reality for many professionals, probably due to the high costs of equipment and the need to implement new procedures in daily routine and reorganization, but using digital flow tools can reduce steps, increase predictability, increase patient acceptance and, of course, provide greater precision.
Intraoral scanners have limitations in taking direct digital impressions, including highly reflective surfaces, very deep subgingival preparations, moisture and bleeding, yet it is necessary in these situations to employ conventional impressions or plaster molds by indirect design, in order to combine the well‐established procedure of using elastomeric materials for a conventional impression and avoid the disadvantages of casting plaster, digitizing the impression itself with a flatbed scanner.
Three models of desktop scanhner can be used: mechanical scanners with probe, which can have great disadvantages due to the possibility of causing distortions in the materials, laser scanners, and white light scanners, which are the most used currently . Newly developed light desktop scanners have advantages over laser scanners in that they analyze a pattern of multiple streaks, whereas laser scanners analyze a pattern of lines.
Basically, desktop scanners have a focus where the objective will be exposed to a light or laser and a scan will be made, giving rise to a digital model that can be used in CAD software. The main advantages of using a desktop scan are lower cost, reduced steps in the procedures, predictability, planning, precision, speed (some cases that would conventionally need five steps can be reduced to two), ability to store information in the cloud, thus reducing the need for physical space, communication with the laboratory, reduced processing errors, and greater patient acceptance. It can be used for obtaining a model for digital diagnostic waxing, making single crowns, inlays, onlays, overlays, making individual tray for total dentures, crown implants, recording of the maxillomandibular relationship with conventional joint scanning, and scanning for making housing plates. Regarding disadvantages, we can mention studies that compare the veracity and precision of desktop scanners using impressions, plaster models, and resin models printed on 3D printers, with impressions being the worst situation with small significant discrepancies [16, 17]. One study reported that plaster cast models may show discrepancies in relation to interior models, but interior models in plaster and resin did not show clinically significant differences.
The desktop scanner can make life easier for the clinician because it is a versatile, accessible tool that uses intuitive software that is easy to learn, promoting improvements in clinical results, but depending on some conventional steps that may be relevant in some cases .
220.127.116.11 Step‐by‐Step Procedures
Using the desktop scanner can be a satisfactory option to help the clinician without relying on a laboratory. The steps required to use this equipment are simple; each device may have some differences but for the most part the steps are very similar.
It is necessary to have some space to install the scanner and a computer that will be used to install the scanning software, store, and possibly send the files. It is important that this computer is used only for this function, avoiding routine functions, which can lead to malfunctions and slowdown, making it difficult to use the equipment.
By following this step‐by‐step description, the clinician will be able to use the desktop scanner without difficulty (Figure 2.14). It is important that the professional follows the specific instructions for each scanner model, but the steps are mostly similar.
- Unpack the scanner from the box and check that all items that come with it are present, such as power supply, accessory parts such as adapter for the model and calibration part.
- Use a UPS to connect the scanner to the electricity, checking the indicated voltage. The vast majority of scanners come with a CD or pen drive to install the software on the computer. Some minimum requirements may be necessary regarding the internal memory configuration of the computer used.
- After installing the software, start the desktop scanner calibration. This can be requested by the system weekly, for better precision and accuracy of the scan.
- During the aforementioned steps, it is important that some information is fed to the planning software inside the computer.
- After performing the steps created in Figure 2.15, we will proceed to the steps described in Figure 2.16.
The countersink process using the specific software of each scanner is extremely simple and intuitive. However, some steps can interface with the final result, such as molding failure, bubbles in the plaster, type of plaster chosen to cast the model, not periodically calibrating the scanner, etc. These can all affect the accuracy and quality of the final work generated.
It is possible to perform the following jobs from a scan performed on a desktop scanner.
- Digital diagnostic wax‐up.
- Individual trays for complete dentures.
- Evidence bases for complete dentures.
- Veneers, crowns, inlay/onlays, in ceramic, zirconia and even metal.
- Occlusion plates.
- Surgical guides.
- Structure for implant prostheses.
- Implant prostheses; in these cases a scan body is necessary, as well as a request for replacement for full crowns on teeth, increasing the accuracy of the scan .
The accuracy of desktop scanners is well reported in the literature. In addition, they are affordable and can provide clinicians with facilities for planning and execution of simple and complex cases during clinical routine .
2.1.4 Facial Scanner
18.104.22.168 Basic Knowledge
Three‐dimensional facial scanning is rapidly developing in dentistry but has applications in many other fields, such as biomedical engineering, design, and 3D animations. Working with a virtual patient who offers information on their facial profile in association with the various CAD‐CAM systems has made it possible to design and manufacture complete dentures fully in a digital way .
A conventional method of prosthetic rehabilitation requires only dental arch models mounted on an articulator, radiographs, and photographs so that a 2D assessment of the maxillofacial region can be obtained . However, the human face is a complex geometric structure with different depths and textures. It is difficult to simulate the real face in a 2D image and assessment of a facial deformity or face asymmetry is also prone to error because 2D analyses do not show the volume of facial proportions that are related to facial harmony. As a consequence, prediction of results and prognosis of treatments can be limited in 2D images .
To overcome these 2D face assessment problems, several 3D facial scanning methods were introduced such as stereophotogrammetry, laser scanning, and structure light scanning [23–26]. These methods provide a 3D simulation of the facial structure surface by generating a digital face model that can be superimposed with radiographic images for 3D face analysis and virtual treatment planning or realistic surgery simulation . Furthermore, the collected scan data can be utilized for multidisciplinary purposes in research and education as well as treatment.
The use of face scanning in dentistry has increased over time and it has applications in the areas of implant dentistry, esthetics, prosthodontics, and periodontics. With the advancement of technology, face scanning can be performed in a way accessible to the professional