Additive manufacturing (AM) A process of constructing objects where material is incrementally added according to a computer-aided design (CAD) file; also known as three-dimensional (3-D) printing.
Augmented reality (AR) A form of virtual reality in which interacting with the real world is through simulation.
Computer-aided design (CAD) A computer technology that designs an object and creates a computer file for manufacture of the design.
Computer-aided manufacturing (or milling) (CAM) The use of software and computer-controlled machinery to automate a manufacturing process.
Cone-beam computed tomography (CBCT) An x-ray three-dimensional (3-D) imaging technology in which the radiation is divergent and forms a cone.
Digital An electronic technology that records or stores information in the form of binary digits (i.e., 1 and 0) or technology characterized by electronic and computerized devices (e.g., digital images).
Digital impression A virtual scan (digital model) of a patient’s dentition and other structures that is generated with laser or other optical scanning devices and converted into a digital format.
Fused deposition modeling (FDM) A three-dimensional (3-D) printing process that uses a continuous filament of a thermoplastic material; also known as fused filament fabrication (FFF) or filament freeform fabrication.
Prototyping The creation, modification, and optimization of two-dimensional or three-dimensional models of objects, which may be the final desired object or an interim object for examination of fit.
Quantitative light-induced fluorescence (QLF) A nondestructive diagnostic method for the detection and assessment of early carious lesions.
Subtractive manufacturing (SM) A process of making 3D objects by successively removing material from a solid block of metal, ceramic, polymer, or composite using computer-aided standard machining processes, such as turning, drilling or milling.
Virtual reality (VR) A computer-generated simulation that allows for interactive experiences.
Digital dentistry is the use of dental technologies or devices that incorporate digital or computer-controlled components to carry out dental procedures rather than using materials and mechanical or electrical tools. The use of digital dentistry can make carrying out dental procedures more efficient than the use of mechanical tools. A variety of digital devices, such as intraoral and facial scanners, cone-beam computed tomography (CBCT), software for computer-aided design (CAD) and computer-aided manufacturing (or milling) (CAM), and three-dimensional (3-D) printing provide new potential alternatives to replace the manual tasks and improve the quality of care and patient experiences. These technologies have several advantages, including accurate and time-saving measurement, electronic storage, and file transmission to automate processes.
How are digital impressions made, and what are their applications in dentistry?
Intraoral Digital Scanner
Intraoral scanner/cameras, similar in size to a dental mirror, are able to show tooth surfaces in 3-D rather than two-dimensional (2-D) photographic images. Such cameras are used in the dental office, without the help of a dental technician. The clear images enable color matching, diagnostic tasks, orthodontic and implant placement, and digital impressions.
Intraoral scanners use light to create accurate 3-D records of the dental arches, using only a beam of infrared light, that are digitally recorded. Such digital impressions almost instantly re-create the positive impression of a patient’s dentition and other structures in a digital format. In contrast, conventional impressions require placing a tray of impression material over the dental arches to create an intaglio of the dentition, from which a positive model must be made. Digital impression techniques are a clinically acceptable alternative to conventional impression methods in the fabrication of crowns and short fixed dental prostheses (FDPs) and implant-supported crowns. Digital impressions are faster, are more comfortable for patients, and shorten chair time. However, digital impressions are currently less accurate for full-mouth and edentulous-jaw impressions.
A physical shade guide is the traditional means of matching a patient’s teeth to restorative materials. However, differences often occur in shade matching as a result of variations among observers (dentist, technician, patient) and sources of illumination. Digital cameras have improved both dental laboratory communication and patient satisfaction. Such images are needed for the selection of materials, as discussed in the CAM section that follows.
What is prototyping?
What are subtractive and additive processes, and what are their relative advantages and disadvantages?
Prototyping technology is based on using computer software and systems to assist in the creation, modification, analysis, and optimization of 2-D or 3-D models of objects. Any computer program that includes computer graphics and engineering functions for manipulation can be classified as CAD software. CAM in dentistry is the construction of a restorative device using the output from the CAD software. CAM may be additive (buildup of a material) or subtractive (removal of material from a larger starting piece).
Which dental applications can be used with CAD-CAM technology?
Indications for CAD-CAM
Many indications and materials are available for chairside CAD-CAM restorations, as shown in the list that follows. Each type of material offers unique features for its indications. The CAD-CAM system represents the process by which these materials are fabricated, and the clinical outcome of the restoration is determined by the restorative material.
Ceramic-, metal-, and resin-based crowns and bridges
Copings and frameworks for metal-ceramic prostheses
Full and partial dentures
Inlays, onlays, partial crowns, and provisionals
Implant abutments and crowns, including screw-retained crowns
Orthodontic printed models and clear appliances
Maryland bridges and veneers
Subtractive Manufacturing—CAM Milling Machines
CAD-CAM crown fabrication was the first subtractive manufacturing introduced to dentistry in late 1980s. With CAD-CAM technology in a dental office, a patient may receive a crown with the same-day delivery and reduced chairside adjustments. Representative CAD-CAM systems are offered by Dentsply Sirona (CEREC) and Planmeca USA (Emerald). This group of equipment can be used to fabricate ceramic and composite inlays, onlays, crowns, and veneers from an optical impression of the prepared tooth made from a digital impression. The restoration is designed using the system’s software and milled from a solid block of ceramic or composite using diamond and carbide burs. Restorations and prostheses may be prepared in a single appointment, which eliminates the impression material, preparation of a model, preparation of a provisional restoration, and laboratory fabrication of the final restoration or prosthesis.
Today’s dental CAD-CAM systems can be divided into four groups. The first group is the chairside systems, such as CEREC from Dentsply Sirona and Emerald from Planmeca USA. The Primescan (Dentsply Sirona) uses blue light-emitting diode (LED) light and smart pixel sensor video imaging for 24 frames per second and processes more than 1 million 3-D data points per second. The Emerald uses a multicolor laser-based system.
The second group is the commercial laboratory systems. For these systems, the dentist should send physical impressions, master models, or raw scans to the laboratory of choice for the fabrication of the final prosthesis.
The chairside system usually operates on a closed-architecture format, which requires the scan to be used only within the manufacturer’s proprietary CAD-CAM workflow, and this system uses its own specific file format for CAD-CAM functions. The laboratory system uses an open-architecture format that allows a variety of file formats, such as STL, OBJ, and PLY. The STL is the most popular file format in the field. The scan data can be easily exported as an STL file format compared with other file formats.
The third group is stand-alone digital impression systems. This type of system is based on an open-architecture format and takes only intra- or extraoral scans. The raw file format is electronically transferred to a designated commercial laboratory for the fabrication of the final prosthesis. The Medit i500 (Medit Corp) works based on 3-D video technology. The TRIOS 3 (3Shape) uses fast confocal microscopy optical scanning technology. The iTero (Align Technology) uses laser light beams based on parallel confocal microscope technology. The True Definition Scanner (Midmark) uses structured pulsating blue light with active wavefront sampling 3-D video technology. The CS 3600 (Carestream Dental) uses LED light with active-speed 3-D video technology.
The fourth group is hybrid systems; these are a kind of mix-and-match system based on an open-architecture format. A hybrid system allows communication between products of many different manufacturers, such as intra- and extraoral scanners, CAD units, and CAM units. The dentist and laboratory can choose their preferred scanners, CAD-CAM software, computer hardware, 3-D printers, and milling machines from a variety of vendors.
The common disadvantages of the laboratory, digital impression, and hybrid systems are the need for multiple clinical appointments, the making of physical impressions, the fabrication of provisionals, the increased total costs of fabrication, and the delayed delivery time compared with the chairside systems.
All classes of dental materials, including ceramics, polymers, and metals, can be processed with CAD-CAM systems. In this chapter, ceramics are discussed, which is the most widely used material, among others.
The CAD-CAM ceramics can be categorized into three main groups, mainly by the glass content, and subgroups by the type of material, as follows:
Aesthetic ceramics with high glass content
Aluminosilicate (feldspathic or synthetic)—This material is a mixture of high-melting glasses, nepheline, and albite, such as the Mark II (VITA North America).
Lucite (40% to 50%) containing glass—The typical material of this group is IPS e.max (Ivoclar Vivadent).
Structural ceramics with low glass content
Lithia disilicate and zirconia reinforced lithia silicate —This material group includes e.max CAD (Ivoclar Vivadent), Suprinity (VITA North America), and Celtra Duo (Dentsply Sirona).
Alumina, spinel, and alumina/zirconia —This material group comprises In-Ceram Alumina, In-Ceram Spinel, and In-Ceram Zirconia (VITA North America).
Structural ceramics without glass content
Polycrystalline alumina (with 3 wt% Mg for grain growth control)—This material group includes VITA All-Cubes (VITA North America).
Polycrystalline zirconia (with 3 to 5 wt% of Y for transformation toughening)—This material group includes VITA YZ HT (VITA North America), CEREC Zirconia Blocks (Dentsply Sirona), IPS e.max ZirCAD LT (Ivoclar Vivadent), and KATANA Zirconia Blocks (Kuraray America).
All materials presented here can be processed by either a chairside or a laboratory milling machine. The commercial labs use disks for bulk production of multiple units, and chairside milling units work with individual blocks. The manufacturers produce only feldspathic (aluminosilicate) blocks for chairside milling. Thus there are no laboratory-milled feldspathic CAD-CAM prostheses.
The advantage of the chairside CAD-CAM systems is that the dentist can create any preparation design to preserve tooth structure as long as enough enamel structure remains for desirable adhesion between the ceramic and the enamel. Because one-visit CAD-CAM dentistry does not require provisional restorations and temporary cement, contamination of the prepared tooth structure is minimized, and the dentist can gain strong bonding for optimal results.
The following clinical case demonstrates a CAD-CAM chairside partial-coverage (inlay or onlay) crown. The occlusal surface of an existing resin composite restoration shows the existence of a large marginal gap but without radiographic evidence of recurrent caries. After the old resin composite restoration was removed, lesions of recurrent caries were revealed. The tooth was prepared to receive a ceramic onlay. Once the cavity preparation was completed ( Figure 15-1, A ), the intraoral scans of the prepared tooth were made ( Figure 15-1, B ). Scans of the unprepared teeth of the opposing arch and the buccal bite registration were also taken (not shown). The next step includes the occlusal relation adjustment ( Figure 15-1, C ) and the design of the prosthesis ( Figure 15-1, D ). The final preview of the milling process prior to the actual manufacturing process is shown in Figure 15-1, E . The CAD-CAM restorations were then tried and inserted with dual-cure resin cement. The final occlusal photo ( Figure 15-1, F ) shows a well-integrated aesthetic ceramic restoration.