CAD/CAM is an acronym for computer-aided design/computer-aided manufacturing. With CAD/CAM, parts and components can be designed and machined with precision using a computer with integrated software linked to a milling device [1]. The advent of CAD/CAM has enabled the dentists and laboratories to harness the power of computers to design and fabricate esthetic and durable restorations [2]. CAD/CAM has become an increasingly popular part of dentistry over the past 25 years [3]. The technology which is used in both the dental laboratory and the dental office can be applied to inlays, onlays, veneers, crowns, fixed partial dentures, implant abutments, and even full mouth reconstruction. CAD/CAM technology was developed to solve three challenges. The first challenge was to ensure adequate strength of the restoration, especially for posterior teeth. The second challenge was to create restorations with a natural appearance. The third challenge was to make tooth restoration easier, faster, and more accurate [4].

History

Computer aided design and manufacturing were developed in the 1960s for use in the aircraft and automotive industries, and were first applied to dentistry a decade later [4]. Dr. Francois Duret of France was the first person to develop a dental CAD/CAM device, making crowns based on an optical impression of the abutment tooth and using a numerically controlled milling machine as early as 1971 [5]. He produced the first dental CAD/CAM restoration in 1983 and demonstrated his system at the French Dental Association’s International Congress in November 1985 by creating a posterior crown restoration for his wife in less than an hour. Dr. Duret later developed the Sopha system [4]. Dr. Werner Mormann of Swizerland was the developer of the first commercial CAD/CAM system. He consulted with Dr. Marco Brandestini, an electrical engineer, who came up with the idea of using optics to scan the teeth. By 1985, the team had performed the first chairside inlay using a combination of their optical scanner and milling device. They called the device CEREC, an acronym for computer assisted ceramic reconstruction [6].

Dr. Dianne Rekow of the United States worked on a dental CAD/CAM system in the mid-1980s with colleagues at the University of Minnesota. This system was designed to acquire data using photographs and a high-resolution scanner, and to mill restorations using a 5-axis machine [7].

Dr. Matts Andersson of Sweden developed the Procera method of manufacturing high precision dental crowns in 1983. He attempted to fabricate titanium copings by spark erosion and introduced CAD/CAM technology into the process of composite veneered restorations. This system later developed as a processing centre networked with satellite digitizers around the world for the fabrication of all ceramic frameworks [8].

CAD/CAM Process

The American Dental Association specifies that a dental restoration must fit its abutment within 50μm. This requirement demands that CAD/CAM systems have a very accurate data collection technique, sufficient computing power to process and design complex restorations, and a very precise milling system [9]. All CAD/CAM systems have three functional components: data capture or scanning to capture and record data about the oral environment (tooth preparation, adjacent teeth and occluding tooth geometry), CAD to design the restoration to fit the preparation and to perform according to conventional dental requirements; and CAM to fabricate the restoration.

Scanner is a data collection tool that measures three-dimensional jaw and tooth structures and transforms them into digital data. There are two different scanning possibilities [10].

Optical Scanners

An optical reading of the surface is possible with a white or coloured light or with laser-beam projection. The obtained data is connected to lines, pictures, or points that then create a dot matrix. To measure the circumference of the object with its undercuts, the object or the device has to be tilted or rotated. To this end, the object must be mounted; the different lines, pictures, or points (measurements) can then be numerically related to one another by a reference point and thus create a precise matrix [11]. The basis of this type of scanner is a collection of three-dimensional structures in a so-called triangulation procedure. Triangulation based scanners project a laser beam on an object at a given angle and the reflected beam then travels at a different angle through a lens. Through this angle the computer can calculate a three-dimensional data from the image on the receptor unit. Unfortunately having separate pathways seriously limits measurements of steep angulations or deep cavities due to beam obscuration, therefore triangulation may miss important information from the walls and bottom surface of an object [12].

Mechanical Scanners 

These systems use a ball, needle or pin to detect and record a surface. The master cast is read mechanically line by line by means of a ruby ball and the three-dimensional structure is measured. The scanner has a high scanning accuracy, where the diameter of the ruby is set to the smallest grinder in the milling system. The drawbacks of this system are long processing time and high expenditure compared to optical scanners [10].

The main performance criteria of a scanner are the following [12]:

• Indication (dies, cavities, FPD) 

• Perception of the preparation line

• Perception of undercuts 

• Time needed for scanning a die

• Time needed for scanning a full arch of teeth

• Precision of measurements

• Mounting system for die and model

• Number of axes

• Resolution of the charge-coupled device (CCD) camera 

• Format of the outgoing data

Software for Computer-Aided Design

Several software programs are commercially available for virtual design of dental restorations on a computer screen. The modelling is performed by a 3-D software. The present software programs greatly differ in performance, user friendliness (handling), and possible indications of restorations. These programs work with a knowledge-based CAD technology with roles and standards proposing a design for the given situation. The operating dental technician must control and modify the suggestions made by the computer. Only a few systems allow the design of the occlusion in relation to digitized opposing dentition. Advanced programs are presently being developed (ADG Weigel, Frankfurt, Germany; Medical Solutions, Essen, Germany). Most systems digitize a check bite registration, which also supplies the jaw relation (Pro 50, DigiDent, Cerec 3). The easiest way to create an occlusion on the screen is to scan a handmade waxup or a diagnostic model (Cerec 3, etkon, Everest, Pro 50, DigiDent) and to match this image onto the virtual die. In most systems, the occlusion is modelled freely on the screen by choosing a proposed tooth form from a data bank and matching it onto the virtual die. Advanced systems allow real time processing of the data on the screen while operating and changing the virtual graphics. When the design is completed, the created 3-D volume model is transformed into machine-readable data, saved in a specific data format (language), and transferred to a production unit (CAM). Having selected a specific CAD system, the user has to employ the data format of this software or system. Most CAD/CAM systems in dental technology operate as closed data systems, i.e. all components, such as the scanner and CAD and CAM units are linked by the company’s specific data format. The manufacturer of the system offers training for startup, support, service, update, and selection of the restorative materials. Moreover, the user can use a hotline in case of a problem [13-15].

In a second, more recently released group of CAD/CAM systems, the 3-D volume model of the design is transferred from CAD to CAM in a neutral data format. This language is an industrially compatible format which allows free choice among different production centers and CAM systems. In these systems, scanner and software use a compatible format (STL) for the data exchange, and the production center is technically open to all 3-D volume models of this language. The main performance criteria of dental CAD are the following:

• Automatic tracing of the preparation line

• Modification of the preparation line on the screen

• Indications (occlusion, inlay, coping, FPD, etc.)

• Opposing teeth on the screen

• Jaw relation in centric occlusion and articulation

• Reduction of the waxup for the framework design

• Cement gap

• Blockout of undercuts

• Dimension and position of the connectors

• Dimension and position of the pontics

• (Minimum) thickness of the framework

• Digital attachments and components

• Design of the margin

• Simultaneous operation of the scanner and CAD software

• Real-time operation of the graphics

• Virtual communication and digital support

• Format used for the data exchange

Hardware (CAM) 

The manufacturing units for the fabrication of the digital 3-D models are either present in the dental laboratory or, if they are expensive, concentrated in a specialized production center. The construction data produced with CAD software are converted into milling strips for the CAM processing and loaded on milling device. Processing devices are distinguished by means of number of milling axis [10,11,16].

3 Axis

The milling machine has degree of movement in three spatial directions X, Y and Z axes. A 3-axis will allow the cutter or the stock material to move in the three axes. The stock material is held in a fixture that moves left and right (first axis) and front to back (second axis), with a spindle that moves up and down (third axis). A three axis mill essentially cuts from top and bottom of the restoration, parallel to the path of insertion. It is not capable of milling undercuts. The advantages of these milling devices are short milling time and less cost. Examples: Inlab (Sirona), Lava, Cercon. 

4 Axis

In this, in addition to 3 axis, stock material can also be turned infinitely variably. Example: Zeno.

5 Axis

In this, the milling is capable of constantly re-orienting the stock material or the spindle, off the path of insertion while simultaneously cutting and moving in the other 3 axes. It can mill undercuts and parts can be tilted off the path of insertion to allow the use of shorter stock material.

The main performance criteria of the CAM systems are the following:

• Financial investment (laboratory vs station)

• Indications (occlusion, inlay, coping, FPD)

• Multiple materials, clinical experience, costs, and availability

• Costs for licenses

• Number of axes

• Size of material (FPD)

• Precision of marginal and internal fit after machining

• Machining time per unit with each material

• Long-term milling up to how many units

• Size of the smallest possible bur for each material

• Time needed for the manual precision adjustments

• Number of tools in the machine

• Requirements for the setup site

• Format used to operate the CAM

• Time required to set up the machine for each dental restoration

The CAD/CAM Systems 

Based on their production methods these systems can be divided into the following groups [2,14]:

• In Office System: Most widely and commercially used in CEREC system. This system can scan the tooth preparation intraorally and by selecting appropriate materials, the dentist can fabricate the restorations and seat it within a single appointment

• CAD/CAM- Dental Laboratory Models: The indirect systems scan a stone cast or die of the prepared tooth in the dental lab. Many of this system produce copings which require the dental technician to add esthetic porcelain for individualization and characterization of the restoration

• CAD/CAM for Outsourcing: Since the design and fabrication of the framework for high strength ceramics is technique sensitive, new technologies using CAD/CAM combined with network machining centre that is outsourcing the framework fabrication using an internet have been introduced

Advantages of CAD/CAM [4,17]

• Speed and Ease of Use

• High quality of restorations

• Saves time and labour

• All scans can be stored on the computer

• Accuracy of impressions 

• Opportunity to view, adjust and rescan impressions 

• No physical impression for patient 

• Saves time and one visit for in-office systems 

• Opportunity to view occlusion 

•  Accurate restorations created on digital models 

• No layering/baking errors 

• No casting/soldering errors

• Cost-effective

• Cross-infection control

Disadvantages of CAD/CAM [4,17]

• High initial cost of equipment and software

• Needs time and money on training 

Common CAD/CAM Systems

Cerec: It is an acronym for Chair side Economic Reconstruction of Esthetic Ceramic. Cerec was introduced in 1980s, improved Cerec 2 was introduced in 1996 and the advanced 3-D Cerec 3 in 2000. Among all dental CAD/CAM systems, Sirona, with their CEREC line of products, is the only manufacturer that currently provides both in-office and laboratory-based systems. With CEREC 1 and CEREC 2, the operator takes an optical scan of the prepared tooth with a charged-coupled device (CCD) camera, and the system automatically generates a 3D digital image on the monitor. The restoration is designed and milled. With newer Cerec 3-D, the operator records multiple images within seconds, enabling clinician to prepare multiple teeth in same quadrant and create a virtual cast for the entire quadrant [2,9,18]. 

Designed restoration is transmitted to a remote milling unit for fabrication. CEREC in lab is a laboratory-based system for which working dies are laser-scanned and a digital image of the virtual model is displayed on a computer screen. A wide range of high strength ceramic blocks are available for the in-lab system, which include Vita In-Ceram blocs and two sintered ceramics: inCoris ZI (zirconium oxide) and inCoris AL (aluminium oxide) (Sirona Dental Systems, LLC). The coping or framework then is either glass-in filtrated (Vita In-Ceram) or sintered (zirconium oxide or aluminium oxide), and the veneering porcelain is added. The most recent developments of CEREC technology include using a step bur that eliminates the need to over mill, the Biogeneric software for easy and friendly design, a faster and quieter milling unit (CEREC inLab MC XL), and CEREC Connect, which is a Web-based communication platform between in-office and CEREC in Lab systems. In vitro evaluation of marginal adaptation of crown of cerec 3-D (47.5 μm±19.5 μm) was better compared with cerec 2 (97.0±33.8 μm).

E4D Dentist

The E4D Dentist system is a newly developed in-office CAD/CAM system. In most clinical situations, digital 3D impressions of the tooth preparation can be obtained through use of its high-speed IntraOral Digitizer (an intraoral laser scanner) without reflective agents. The operator performs multiple scans from various angles to maximize collection of data points, which allows the software to re-create true morphology. The Design Center and milling unit allow dentists to create inlays, onlays, veneers, and crowns in one appointment. The manufacturer, D4D Technologies LLC, collaborates with three major corporations in the dental industry. Sales, marketing and distribution are handled by Henry Schein, Inc (Melville, NY), while restorative materials are supplied by 3M ESPE and Ivoclar Vivadent, Inc [4,9].

DCS Precident 

It comprises of a Preciscan laser Scanner and Precimill CAM multitool milling center. The DCS Dentform software automatically suggests, connector sizes and pontic forms for bridges. It can scan 14 dies simultaneously and mill up to 30 frameworks unit in one fully automated operation. Materials used with DCS include porcelain, glass ceramic, Vita In-Ceram, dense zirconia, metals, and fiber-reinforced composites. This system is one of the few CAD/CAM systems that can mill titanium and fully dense sintered zirconia. An in vitro study showed that marginal discrepancies of alumina and ziroconia based posterior fixed partial denture machined by the DCS system was between 60 μm to 70μm [2,9].

Everest

Introduced in 2002, the Everest system consists of scan, engine, and therm components. The operator fixes reflection free gypsum cast into the scanning unit where it is scanned by a CCD camera in a 1:1 ratio, with an accuracy of measurement of 20 μm. The system automatically generates a digital 3D model by computing 15-point photographs. The operator then designs the restoration on the virtual 3D model with Windows-based software. The machining unit has five-axis movement that is capable of producing detailed morphology and precise margins from a variety of materials including leucite-reinforced glass ceramics, partially and fully sintered zirconia, and titanium. Partially sintered zirconia frameworks require additional heat processing in its furnace. The marginal adaptation for Everest crowns was reported as 32.79 (±6.82μm) and 33.72 (±6.69μm) [9,19].

Cercon

Also launched in 2002, the Cercon system initially was referred to as a CAM system because it did not have a CAD component. At that time, the operator needed to make a wax pattern (coping) with a minimum thickness of 0.4 mm. Subsequently, the system scanned the wax pattern and the Cercon Brain milling unit milled a zirconia coping from proprietary presintered zirconia blanks. The coping then was sintered in the Cercon Heat furnace (1350° C) for 6 to 8 hours. Low-fusing, leucite-free Cercon Ceram S veneering porcelain was used to provide the esthetic contour. In 2005, DENTSPLY Ceramco introduced the Cercon Eye 3D laser optical scanner and Cercon Art CAD design software. Now, as a complete CAD/CAM system, Cercon can produce single units and bridges up to nine units from presintered zirconia milling blocks that are offered in white and ivory shades without any infiltration required. In an in vitro study, the marginal adaptation for Cercon all-ceramic crowns and fixed partial dentures was reported as 31.3 μm and 29.3 μm, respectively [9,20].

Procera All Ceram System

Procera/AllCeram introduced in 1994, it is the first system which provided outsourced fabrication using a network connection. Two types of scanners are available to dental laboratories-Procera Piccolo for single-unit restorations and Procera Forte for single- and multiple-unit restorations. First, the scanning stylus is used to create 3D images of the master dies, which are sent to the processing centre via modem. The processing centre (located In New Jersey or Sweden) then generates enlarged dies designed to compensate for the shrinkage of the ceramic material. Copings are manufactured by dry pressing high-purity alumina powder (> 99.9%) against the enlarged dies. These densely packed copings then are milled to the desired thickness. Subsequent sintering at 2000°C imparts maximum density and strength to the milled copings. The copings are returned to the laboratory for a technician to apply the veneering porcelain and complete final occlusal adjustment and finishing on the working cast. 

The complete procedure for Procera coping fabrication is very technique-sensitive because the degree of die enlargement must precisely match the shrinkage produced by sintering the alumina or zirconia. The recommended preparation marginal design for a Procera/AllCeram restoration is a deep chamfer or shoulder with a rounded internal line angle and a well-defined cavosurface finish line with a recommended coping thickness of 0.4 mm to 0.6 mm. Nobel Biocare USA LLC has introduced various implant abutments for its Procera system-titanium (1998), alumina (2002), and zirconia (2003). The system also is capable of generating alumina (two to four units) and zirconia (up to14 units) bridge copings. However, the occlusal-cervical height of the abutment should be at least 3 mm, and the pontic space should be less than 11 mm. According to recent research data, the average marginal gap for Procera/AllCeram restorations ranges from 54 μm to 64 μm. Literature also confirms that Procera restorations have excellent clinical longevity and strength. The flexural strength for Procera alumina is 687 MPa and for Procera zirconia is 1200 MPa [2,9,21,22].

CICERO System

 It stands for computer integrated crown Reconstruction. Introduced by Denison et al in 1999, it includes optical scanning, metal and ceramic sintering and computer assisted milling to obtain restoration. Basic reconstruction includes layered life like ceramic for natural esthetics; a precision milled occlusal surface and a machined high strength ceramic core. The aim of CICERO is to mass produce ceramic restoration at one integrated site. It includes rapid custom fabrication of high strength alumina coping and semi-finished crowns to be delivered to dental laboratories for porcelain layering / finishing [2].

Lava CAD/CAM System 

Introduced in 2002, the Lava system uses a laser optical system to digitize information from multiple abutment margins and the edentulous ridge. Lava Design 4.0 CAD software automatically finds the margin and suggests a pontic. The framework is designed to be 20% larger to compensate for sintering shrinkage. After the design is complete, the system software recommends a properly sized semi sintered zirconia or yttria stabilized tetragonal zirconia poly crystals (Y-TZP) block for milling. The block is bar coded to register the special design of the block. The computer-controlled precision milling unit can mill 21 copings or bridge frameworks automatically without supervision or manual intervention. Milled frameworks then undergo sintering to attain their final dimensions, density, and strength. The system also has eight different shades to colour the framework for maximum esthetics. The shaded framework is returned to the laboratory for a technician to apply the veneering porcelain and complete die restoration. Since 2006, laboratories can purchase a standalone scanner. Lava Scan ST and send the digital data to an authorized Lava Form milling centre [9,23].

TurboDent 

The TurboDent System (TDS) milling center, with its headquarters in Taiwan, began full production in 2003. With this system, the operator scans the stone model and wax-up with the TDS Scanner, and the dental prosthesis is designed by the operator using the TDS Designer. The TDS Designer is a design software package that includes a digital wax-up tool and a comprehensive library of wax-up designs, enabling various prostheses designs to be input and modified by the operator. The five-axis TDS Cutter is capable of milling a wide range of restorations, such as inlays, onlays, veneers, copings, bridge frameworks, custom implant abutments, and implant bars, from titanium or ceramic material. Like the Procera system, casts and dies may be scanned from anywhere in the world using the TDS Scanner and electronically transmitted to the milling center for design, fabrication, and finishing. In 2007, TDS launched a new software module, TDS Implant Smart, that integrates computed tomography scan technology to create a blueprint to place the implants of choice virtually. Additionally, it allows the technician to provide a comprehensive range of services to include fabricating a surgical stent for implant placement, a customized titanium or zirconia implant abutment, temporary crown, and final restoration. Although there is no literature regarding the marginal fit of the TDS, the manufacturer's internal data suggested that its average marginal gap for a titanium coping is 15 μm [9,24].

Advances in computer technology now enable cost-effective production of individual pieces. Dental restorations produced with computer assistance have become more common in recent years. Most dental companies have access to CAD/CAM procedures, either in the dental practice, the dental laboratory or in the form of production centers. Dentists, who will be confronted with these techniques in the future, require certain basic knowledge if they are to benefit from these new procedures.

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