CAD CAM in dentistry / international orthodontics training center


Published on

Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.

Published in: Education, Technology, Business
  • Be the first to comment

No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

CAD CAM in dentistry / international orthodontics training center

  1. 1. INTRODUCTION : “Everything is perfect in the universe, even our desire to improve it.” Such quest towards perfection in our field, has opened up several new range of systems. One such system is CAD-CAM. Computer-Aided Design and Computer-Aided Manufacture (CAD/CAM) systems have been used for many years in various industries, notably the automotive industry, but are now finding applications development in dentistry. CAD : CAD is the use of computer systems in the design and development of a product. The computer is used as an extended drawing board, allowing three-dimensional modeling and design. Mathematical modeling of the structure allows some aspects of its performance to be assessed before it ever leaves the drawing board. CAM : CAM is the use of a computer system to operate machine tools. This allows the shaping of materials to form structures and devices. The computers controlling the machine tools can operate from instructions set up by the computer-aided design system. In this way a complete integrated system is set up. The object to be made is designed on a computer screen and then the design is implemented by the computer.
  2. 2. BASIC ARCHITECTURE OF CAD-CAM : Restorative dentistry has been restricted by the range of fabrication technologies available. Direct placement restorations are limited to the alloying of dental amalgam, acid-base reactions or the polymerization of resins. Laboratory-fabricated restorations are limited to lost-wax casing, porcelain sintering or resin polymerization. This restricts the range of materials which can be used. CAD/CAM systems open up a range of new material systems by providing a new method for the control of shape. The major limiting factor in applying CAD/CAM technology to dental restorations is that the preparation of the tooth is the prime factor which determines the shape of the final restoration. This means that some method of scanning the tooth preparation accurately needs to be employed. Various methods of achieving this are being tried. The first system which became available commercially was developed in Zurich by Werner Mormann and marketed by Siemens of Germany. This is the ‘CEREC” system. At the time of writing this system is the only commercially- available chair-side dental ACD/CAM system on the many scientific studies and over 1000 machines are in clinical use. The ‘CEREC’ concept is the ingenious result of a sophisticated analysis of the requirements of a dental restorative system and the application of logical problem reduction. This is combined with an elegant and effective engineering solution, matched to the problem-reduction model. The tooth preparation is rationalized to exclude the need for internal machining of the ceramic blank. This allows speedy production of the final restoration by a turbine-driven diamond milling disk in a single pass along the ceramic blank. The topography of the tooth preparation is recorded optically in a fraction of a second and a digital model created in the computer.
  3. 3. PROCEDURE : (also see CD) The optical impression : In order to make the surface of the tooth visible to the infra-red illuminator in the active camera, it is necessary to coat the tooth with titanium oxide power. This highly-reflective powder is sprayed on as a dry dust. The tooth is first coated with a polysorbate film, the imaging liquid. This holds the powder in place. A light emitting diode projects the image of a grid onto the tooth surface. The camera observes this grid from a slight angle. Vertical contour of the cavity is observed as a lateral shift in the lines of the grid brought about by a parallax effect. This shift is used to determine the physical measurement of height. Software and the restoration design : Once a three-dimensional model of the tooth preparation is recorded the restoration must be designed on top of it. The first generation software required some level of design intervention by the operator but as the software has become more sophisticated less skill is needed. The operator maps out the base of the restoration by placing plotting points on the photograph of the cavity which appears on a computer monitor. The machine extrapolates across this area and determines the true topography of the cavity floor. The operator next outlines the approximal surface and the machine suggests the placement of the marginal ridge. These features may be edited easily. The points are joined up by the computer which then locates the occlusal margin of the cavity using a wall-finding algorithm which looks progressively up the wall of the cavity until a horizon is located. It identifies this as the cavity edge. These data are used to construct a wire-frame model of the restoration. Edition of the data is possible to alter the external profile of the final restoration. The wire-frame model is stored to disk and the data
  4. 4. are used to drive a milling machine which shapes a block of ceramic to the required form. After the volume model has been created, a ceramic block is inserted into the milling machine and the device renders the final restoration. This is the original hydraulic turbine version. An electric drive is now available and provides a finer surface finish on the ceramic restoration and a much improved cutting efficiency. Milling with a rotary disk is simple and effective but there are certain limitations of cut which are implicit in the system. The preparations cut in the tooth must be designed to take these limitations into account. Possible : A : External curves in the plane of the cutting disk on any surface. B : External curves perpendicular to the plane of the cutting disk on any surface. C : Straight steps across the whole of a surface in the plane of the cutting disk. Not possible : X : Steps with risers at angles to the plane of the cutting disk. Y : Internal curves with a radius smaller than that of the cutting disk. Z : Undercut surfaces. Steps in the same plane as the disk are not possible nor are any areas of internal milling such as would be needed to fabricate a crown. This limitation affects the design of cavity which can prepared. However, most cavity surfaces can be restored with modifications to the traditional cavity design. Machining such a small item as a dental crown, bridge or inlay requires high levels of precision, especially when creating an internal fitting surface such as that of crown. A capstan-head milling machine is needed to fabricate the inner surfaces of crowns as a number of cutting instruments
  5. 5. will be needed to create the shape. Such machines take much greater time in manufacturing are likely to be limited to laboratory use and will not allow single-visit crown placement. Cost appears to be the greatest obstacle to commercial realization of working systems. Laboratory-based CAD/CAM systems are available and mostly rely on digitizing data from dental models which are cast from conventional impressions. The digitizing systems are based on mechanical stylus tracing and this takes a considerable time to do. It is more than reasonable to look at the direction in which technology is moving and predict that the next stage of tooth reconstruction which will come to the attention of the computer technologist is the cutting of the tooth preparations. In this way the machine could optimize all stages of rebuilding or replacing a tooth. Structural analysis can be integrated into computer-aided design. This is known as finite element analysis or FEA. FEA allows the distribution of stresses in a structural design to be analysed. From this information the design of the structure can be modified in order to optimize the stress distribution both in the structure itself and in the structures which support it. Integrating such a design system into a dental CAD/CAM system is a formidable but achievable task which would allow the development of restorations far superior to any of today.
  6. 6. RESTORATIVE MATERIALS FOR CAD/CAM : CAD/CAM systems based on machining of presintered alumina or zirconia blocks in combination with specially designed veneer ceramics satisfy the demand for all-ceramic posterior crowns and fixed partial dentures. Many ceramic materials are available for use as CAD/CAM restorations. Common ceramic materials used in earlier dental CAD/CAM restorations have been machinable glass ceramics such as Dicor or Vita Mark II. Although monochromatic, these ceramic materials offer excellent esthetics, biocompatibility, great color stability, low thermal conductivity, and excellent wear resistance. They have been successfully used as inlays, onlays, veneers, and crowns. However, Dicor and Vita Mark II are not strong enough to sustain occlusal loading when used for posterior crowns. For this reason, alumina and zirconia materials are now being widely used as dental restorative materials. These ceramic agents may not be cost-effective without the aid of CAD/CAM technology. For instance, In-Ceram, first described by Degrange and Sadoun, has been shown to have good flexural strength and good clinical performance. However, the manufacture of conventional In-Ceram restoration takes up to 14 hours. By milling copings from presintered alumina or zirconia blocks within a 20 minute period and reducing the glass infiltration time from 4 hours to 40 minutes, CEREC inLab decreases fabrication time by 90%. Zirconia is strong and has high biocompatibility. Fully sintered zirconia materials can be difficult to mill, taking 3 hours for a single unit. Compared with fully sintered zirconia, milling, restorations from presintered or partially sintered solid blocks is easier and less time-consuming, creates less tool loading and wear, and provides higher precision. After milling, In- Ceram spinell, alumina, and zirconia blocks are glass infiltrated to fill fine
  7. 7. porosities. Other machinable presintered ceramic materials are sintered to full density, eliminating the need for extensive use of diamond tools. Under stress the stable tetragonal phase may be transformed to the monoclinic phase with a 3% to 4% volume increase. This dimensional change creates compressive stresses that inhibit crack propagation. This phenomenon, called “transformation toughening,” actively opposes cracking and gives zirconia its reputation as the “smart ceramic.” The quality of transformation toughness and its affect on other properties is unknown. Zirconia copings are laminated with low fusing porcelain to provide esthetics and to reduce wear of the opposing dentition. If the abutment lacks adequate reduction the restoration may look opaque. Because they normally are not etchable or bondable, abutments require good retention and resistance form. Alumina and zirconia restorations may be cemented with either conventional methods or adhesive bonding techniques. Conventional conditioning required by leucite ceramics (eg, hydrofluoric acid etch) is not needed. Microetching with Al2O3 particles on cementation surfaces removes contamination and promotes retention for pure aluminum oxide ceramic. Two in vitro studies recommended that a resin composite containing an adhesive phosphate monomer in combination with a silane coupling/bonding agent can achieve superior long-term shear bond strength to the intaglio surface of Procera AllCeram and Procera AllZirkon restorations. CAD/CAM systems also can be applied to restorations requiring metal and are used to fabricate implant abutments and implant-retained overdenture bars. The DCS system can fabricate crown copings from titanium alloy with excellent precision. Several articles have reported the extension of CAD/CAM technology to the fabrication of maxillofacial prostheses such as the artificial ear.
  8. 8. Review of Common CAD/CAM Systems : CAD/CAM systems may be categorized as either in-office or laboratory systems. Among all dental CAD/CAM systems, CEREC is the only manufacturer that provides both in office and laboratory modalities. Similar to CAD/CAM systems have increased significantly during the last 10 years and include DCS Precident, Procera, CEREC inLab, and Lava. CAM capabilities without the design stage. Several of the more common dental CAD/CAM systems are described below. CEREC : With CEREC 1 AND CEREC 2, an optical scan of the prepared tooth is made with a couple charged device (CCD) camera, and a 3-dimensional digital image is generated on the monitor. The restoration is then designed and milled. With the newer CEREC 3D, the operator records multiple images within seconds, enabling clinicians to prepare multiple teeth in the same quadrant and create a virtual cast for the entire quadrant. The restoration is then designed and transmitted to a remote milling unit for fabrication. While the system is milling the first restoration, the software can virtually seat the restoration back into the virtual cast to provide the adjacent contact while designing the next restoration. CEREC inLab is a laboratory system in which working dies are laser- scanned and a digital image of the virtual model is displayed on a laptop screen. After designing the coping or framework, the laboratory technician inserts the appropriate VITA In-Ceram block into the CEREC inLab machine for milling. The technician then verifies the fit of the milled coping or framework. The coping or framework is glass infiltrated and veneering porcelain is added. One recent in vitro evaluation of CAD/CAM ceramic crowns that compared the marginal adaptation of CEREC 2 with CEREC 3D concluded
  9. 9. that crown adaptation for CEREC 3D (47.5 ± 19.5 µm) was significantly better compared with CEREC 2 (97.0 ± 33.8 µm). DCS Precident : The DCS Precident system is comprised of a Preciscan laser scanner and Precimill CAM multi tool milling centre. The DCS Dentform software automatically suggests connector sizes and pontic forms for bridges. It can scan 14 dies in 1 fully automated operation. Materials used with DCS include porcelain, glass ceramic, 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 was conducted evaluating the marginal fit of alumina – and zirconia-based 3-, 4- and 5- unit posterior fixed partial dentures machined by the DCS President system. They concluded that the system easily met the requirement of less discrepancy than 100 µm. Another study evaluated that DCS system for fabricating titanium copings. The mean values of marginal fit for the individual crowns ranged from 21.2 ± 14.6 µm to 81.6 ± 25.1 µm. The mean value for all crowns was 47.0 ± 31.5 µm. Procera : Procera / AllCeram was introduced in 1994 and according to company data, has produced 3 million units as of May 2004. Procera uses an inhnovative concept for generating its alumina and zirconia copings. First, a scanning stylus acquires 3D images of the master dies that are sent to the processing center via modem. The processing center 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. The complete produce for Procera coping fabrication is very technique
  10. 10. sensitive because the degree of die enlargement must precisely match the shrinkage produced by sintering the alumina or zirconia. According to recent research data, the average marginal gap for Procera/AllCeram restorations ranges from 54µm to 64µm. Literature also confirms that Procera restorations have excellent clinical longevity and strength. The flexural strength for Procera alumina is 687 MPa and for zircoina is 1200 MPa. Procera also is capable of generating AllCeram 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. The recommended preparation marginal design for Procea is a deep chamfer finish line with a recommended coping thickness of 0.4 mm to 0.6 mm. Lava : Introduced in 2002, Lava uses a laser optical system to digitize information from multiple abutment margins and the edentulous ridge. The Lava 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, a properly sized semisintered zirconia block is selected for milling. The block is bar coded to register the special design of the block. The computer-controlled precision milling unit can mill out 21 copings or bridge frameworks without supervision or manual intervention. Milled frameworks then undergo sintering to attain their final dimensions, density, and strength. The system also has 8 different shades to color the framework for maximum esthetics. Hertlein and colleagues tested the marginal adaptation of yttria zirconia bridges processed with the Lava system for 2 milling time (75 minutes vs 56 minutes). They concluded that the milling time does not affected the marginal adaptation (61 ± 25µm vs 59 ± 21 µm) for 3-unit zirconia bridge frameworks.
  11. 11. Everest : Marketed in 2002, the Everest system consists of scan, engine, and therm components. In the scanning unit, a reflection-free gypsum cast is fixed to the turntable and scanned by a CCD camera in a 1:1 ratio with an accuracy of measurement of 20 µm. A digital 3D model is generated by computing 15 point photographs. The restoration is then designed on the virtual 3D model with Windows-based software. Its machining unit has 5- axis movement that is capable of producing detailed morphology and precise margins from a variety of materials including leucite-reinforced glass ceramics, titanium. Partially sintered zirconia frameworks require additional heat processing in its furnace. Cercon : The Cercon System is commonly referred to as a CAM system because it does not have a CAD component. In this system scans the wax pattern and mills a zirconia bridge coping from presintered zirconia blanks. The coping is then sintered in the Cercon heat furnace (1,3500 C) for 6 to 8 hours. A low-fusing, leucite-free Cercon Ceram S veneering porcelain 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. One of the most important criteria in evaluating fixed restorations is marginal intergrity. Evaluating inlay restorations, Leinfelder and colleagues reported that marginal discrepancies larger than 100µm resulted in extensive loss of the luting agent. O’Neal and colleagues reported the possibility of wear gap dimension exceeded 100 µm. Essig and colleagues conducted a 5- year evaluation of gap wear and reported that vertical wear is half of the horizontal gap. The wear of the gap increased dramatically in the first year, becoming stable after the second year.
  12. 12. McLean and Von Fraunhofer proposed that an acceptable marginal discrepancy for full coverage restorations should be less than 120 µm. Christensen suggested a clinical goal of 25µm to 40µm for the marginal adaptation of cemented restorations. However, most clinicians agree that the marginal gap should be no greater than 50µm to 100µm. Current research data indicate that most dental CAD/CAM systems are now able to produce restorations with acceptable marginal adaptation of less than 100 µm.
  13. 13. CONCLUSION : CAD/CAM systems have dramatically enhanced dentistry by providing high-quality restorations. The evolution of current systems and the introduction of new systems demonstrate increasing user friendliness, expanded capabilities, and improved quality, and range in complexity and application. New materials also are more esthetic, wear more nearly like enamel, and are strong enough for full crowns and bridges. Dental CAD/CAM technology is successful today because of the vision of many great pioneers. As Duret, concluded in his article in 1991, “The systems will continue to improve in versatility, accuracy, and cost effectiveness, and will be a part of routine dental practice by the beginning of the 21st century. “The true work of art is but a shadow of the divine perfection” – Michelengelo.