Written by Mingway Lee, DDS, and Hong-Tzong Yau, PhD Thursday, 31 August 2006 19:00
In recent years, the use of CAD/CAM systems has become popular in dentistry. The CAD/CAM systems that are used in dental applications generally consist of 3 modules: (1) a scanner, which scans a solid model and converts the model into digital data; (2) a design software package, which is used to design and modify the digital model; and (3) a milling machine, which mills the designed model using a selected material.
The development of CAD/CAM systems for dental applications first began in Europe in the 1970s. The first system to be introduced into the dental market was the CEREC1 (Sirona) for aesthetic, all-ceramic, chairside single- or dual-surface inlays using VITA-BLOCS Mark II (Vident). The new CEREC 3D system (Sirona Dental Systems) introduced in 2003 uses intraoral imaging and computer technology to fabricate dental restorations in the dental clinic to shorten treatment time. Precise optic lenses capture the shape of the tooth preparation. A virtual model of a patientís teeth is then created using a computer. The dentist designs the virtual model using CAD software, and then a milling machine directly mills the restoration from a block of ceramic material. Finally, the dentist bonds the milled restoration into the patientís mouth. The complete procedure takes approximately one hour. The materials used in the CEREC 3D system (sintered ceramic blocks) are close to natural teeth in strength, beauty, and function. Indications include inlays, onlays, veneers, and crown restorations.
In addition to the development of dental CAD/CAM systems such as CEREC 3D for use in dental clinics, more CAD/CAM systems are being developed for the needs of dental laboratories. The primary use of CAD/CAM systems by dental laboratories is for single-unit and multi-unit crown and bridge restorations. The steps in fabricating these types of dental restorations are as follows: (1) a stone model of the prepared teeth is made from an impression; (2) the stone model is scanned and converted to digital data; (3) design of the model is carried out using designing software; and (4) a milling machine is used to mill the restorations. These types of CAD/CAM systems are able to fabricate many varieties of restorations at a lower cost while maintaining good quality.
Figures 1a to 1c. TDS modules: TDS Scanner (a), TDS Designer (b), and TDS Cutter (c).
Figure 2. TDS Designer allows user to determine the amount of internal relief for cement space and the copingís adaptation to the abutment tooth.
Figure 3. Margin of tooth preparation has been identified.
Figure 4. Digital wax pattern and the occlusion registration in position for digital wax-up.
Figure 5. Digital wax pattern after occlusal adjustment.
Figure 6. Result of cut-back before rounding of sharp corners.
Figure 7. Adjustment of connector size and location.
Figures 8a and 8b. TDS milling machine can process different types and shapes of materials: titanium blank and titanium bar (a), and ceramic block and ceramic blank (b).
|Figure 9. TDS-processed Vita In-Ceram Alumina coping and abutment fit (unit: µm). Image courtesy of the Department of Mechanical Engineering, National Chung Cheng University, Taiwan.|
Figure 10. Pretreatment frontal view.
Figure 11. Poor oral hygiene, leaking restorations, discolored and hypocalcified enamel on most of the patientís teeth.
Figure 12. Palatal view of TDS CAD/CAM-processed In-Ceram Alumina copings.
Figure 13. Palatal view of completed TDS In-Ceram Alumina crowns.
Figure 14. The all-ceramic crowns provide excellent aesthetic result.
Figure 15. Patient's oral hygiene has significantly improved 2 weeks following cementation.
Figure 16. Close-up view shows healthy gingival tissues.
Figure 17. Profile view shows the excellent aesthetic appearance the TDS CAD/CAM-processed In-Ceram Alumina crowns provide.
ADVANTAGES OF DENTAL CAD/CAM SYSTEMS
Why use CAD/CAM systems to fabricate dental restorations? Dental CAD/CAM systems have advantages that cannot be matched with respect to the strength of materials and precision of the restorations. Dental materials used by CAD/CAM systems are manufactured using standardized manufacturing procedures under strict quality control. These materials are generally better in quality, strength, and durability than those used to make dental restorations in the traditional casting process. Furthermore, in the milling process, the materials are not subjected to the high casting temperatures that can lead to problems. Therefore, dental restorations fabricated from CAD/CAM systems possess optimum strength (all-ceramic materials have a flexural strength > 500 MPa). In terms of a restorationís precision, because of the accuracy of the scanner, software, and milling machine in a CAD/CAM system, the fit of the dental restorations is quite predictable.
TurboDent System (TDS [Pou Yuen Technology]) is an integrated and advanced CAD/CAM system that meets the need of dental laboratories. TDS consists of the following modules: TDS Scanner, TDS Designer software, and TDS Cutter (Figures 1a to 1c). Brief introductions to the system's features are given below:
•Quick and precise scanning and conversion of stone model to digital model.Scanning converts a solid object to digital data. Precision of the scan is the determining factor in the fit of a CAD/CAM restoration. Generally, the scanning precision required for dental restorations is about 30 µm. TDS Scanner utilizes laser scanning to achieve a precision of 10 µm, and it only takes approximately 2.5 minutes to scan a single unit.•Accurate margin line processing, coping fitting, digital wax-up, and cut-back design.The software is the brain of a CAD/CAM system. TDS Designer software uses advanced technology to quickly and accurately capture and design the margin line to ensure accurate marginal adaptation. TDS Designer provides parameters for users to set the ideal thickness of the coping, identify the areas and the amount of relief for cement space, as well as determine the adaptation of the coping to the abutment tooth (Figures 2 and 3). There are three ways to design the copings. First, a traditional wax pattern can be made and scanned into TDS Designer. Second, a uniform thickness of coping can be made directly by the software. Third, a coping can be made by using digital wax-up. Digital wax-up design is the trend in future software development for dental applications. TDS Designer has a library of digital wax patterns and digital wax knives that lets users read, edit, and modify pattern morphology to meet different dental situations. One unique feature of TDS Designer is the virtual simulation of occlusion. Currently, a static occlusion can be achieved by scanning articulated models or occlusal registration for an accurate occlusal design. After completion of the digital wax pattern, computer-controlled cut-back enables uniform ceramic buildup on copings to ensure aesthetic appearance, functionality, and durability of the finished restorations (Figures 4 to 7).•High-speed 5-axis milling.TDS Cutter is one of the very few dental milling machines that has the capability of 5-axis milling. This 5-axis milling enables the fabrication of sophisticated restorations such as a 1-piece, full-arch titanium bridge and custom implant abutments. The machine uses precise milling tools (the finest one has a 0.3-mm radius) for fine machining, which completely mills the details of the digital model. This machine automatically measures and calibrates milling tools prior to milling to prevent machining errors due to wear and tear of the tools. Due to its high speed of milling, the TDS machine is capable of milling a variety of restorations using different types of materials, including metal, ceramic, and plastic (Figures 8a and 8b).•Choices of materials.Metal and ceramic are the two primary materials used in processing. Titanium is the metal of choice for its strength and biocompatibility, especially when it is used for restoring dental implants. All-ceramic restorations are gaining popularity in dentistry for their aesthetic appearance. Zirconia, alumina, and feldspar are the all-ceramic materials that are used in the machine processing. Zirconia possesses optimum natural appearance, strength, and translucency. Two kinds of zirconia are used in dental CAD/CAM systems. The first is pure zirconium dioxide (yttrium-stabilized zirconium dioxide), such as Vita In-Ceram 2000 YZ (Vident) and Lava (3M ESPE); it has a flexural strength that exceeds 900 MPa and is indicated for substructures of long-span bridges and anterior and posterior single copings (4 units and above). The second is composite zirconia (aluminum oxide reinforced with zirconium oxide), such as Vita In-Ceram Zirconia (Vident); it has a flexural strength of 600 MPa and is suitable for posterior crowns or short-span bridges (up to 3 units). Alumina has a flexural strength of 500 MPa. It has optimum translucency and is thus suitable for single crowns and 3-unit anterior bridges. Spinell ceramics MgAl2O4, a ceramic material based on alumina and magnesium oxide, has a flexural strength of 400 MPa. This material has a better translucency and less strength than alumina. It is suitable for single anterior crowns. Feldspar ceramic, such as Vitabloc Mark II and TriLuxe (Vident), has strength and translucency close to natural teeth. It is suitable for single crowns, veneers, inlays, and onlays. The fitting of the precision-milled TDS all-ceramic coping is demonstrated in Figure 9.
Clinical applications of TDS include metal and all-ceramic crowns and bridges, onlays, inlays, and veneers, as well as a variety of implant restorations. The system can also produce custom implant abutments in both zirconia and titanium. TDS has developed an implant surgical planning and template system. This not only provides guidance for implant surgery but also allows dentists to integrate the restorative planning from provisional restorations to permanent restorations at the time of surgical planning. Following is a clinical example of TDS CAD/CAM-processed all-ceramic single crowns.
Patient Dental History
•Female patient in early 20s, good general health, poor oral hygiene, sensitivity in most of her teeth.
•Chief complaint: Patient wishes to have veneers for her 6 upper front teeth to improve aesthetic appearance (Figure 10).
Diagnosis and Treatment Planning
•Oral hygiene poor, gingival bleeding upon probing, gingivitis.
•Hypocalcified and discolored enamel on most of the teeth.
•Multiple existing restorations with evidence of leaking and decay (Figure 11).
•Patient previously received orthodontic treatment with relapse at present.
•Due to the extent of the existing fillings in the upper anterior teeth, which also exhibit multiple areas of decay as well as poor quality of enamel, treatment for porcelain veneers was not favorable for long-term prognosis.
•Treatment plan of 6 CAD/CAM-processed all-ceramic crowns (Vita In-Ceram Alumina) was made and agreed to by the patient with a signed informed consent form.
•Preoperative shade was verified with Easyshade (Vident). Although the existing shade was C2 (cervical), C2 (middle), and EN1 (incisal), the patient had no intention of matching the discolored teeth in her mouth. It was decided to use A1-A1-EN1 for the shades of the 6 all-ceramic crowns. The original tooth shade was recorded and noted in the progress note to avoid future confusion. A preoperative impression ([AlgiNot] Kerr) and an occlusal registration ([Blu-Mousse] Parkell) were taken for provisional restorations and record keeping.
•Oral hygiene instruction, prophylaxis, and scaling were performed. The patient was instructed to use antiseptic mouthwash (Listerine [Pfizer]) to reduce gingival inflammation. Abutment tooth preparation was completed following the requirements of all-ceramic crown preparation guidelines (2-mm incisal reduction, 1.2-mm to 1.5-mm facial reduction, 1-mm to 1.2-mm lingual reduction, and a circumferential 1.0-mm shoulder margin with rounded internal line angle). A full-arch impression was taken with Chromaclone PVS impression material (Ultradent Products). An opposing arch impression was taken with AlgiNot, and an interocclusal registration was taken with Blu-Mousse. To provide maximum protection during the provisional stage, the laboratory-processed provisional crowns were cemented with Temp Advantage (GC America), which is a eugenol-free temporary cement that contains fluoride for caries protection, chlorhexidine for antibacterial action, and potassium nitrate to reduce sensitivity.
•A stone model of abutment teeth was made and articulated with the opposing model.
•The working dies of abutment teeth were trimmed.
•The working dies were scanned with the TDS Scanner and converted into digital models.
•Digital wax patterns were made and then cut back with the TDS Designer software for coping fabrication.
•Data was transferred to CAM software for conversion to CNC (computer numerical control) data for the TDS Cutter. A Vita In-Ceram Alumina blank was positioned in the machine for processing.
•Processed copings were placed on the working die to verify the fit.
•The copings were then clean-fired and glass infiltration-fired.
•Excess glass was removed. The copings then underwent several glass control firings.
•The glass-infiltrated copings were ready for porcelain veneering (Figure 12).
•The copings were veneered with Vita VM7 porcelain (Vident).
•A lingual view of the completed In-Ceram Alumina crowns is depicted (Figure 13).
Try-In and Delivery of Completed Restorations
•The provisional crowns were removed and the abutment teeth cleansed with Consepsis (Ultradent Products).
•Fitting of all-ceramic crowns was verified with AccuFilm IV (Parkell). The internal surfaces of the copings were not adjusted. Instead, the corresponding high spots on the abutment teeth were removed with a fine diamond. Proximal contacts were verified and adjusted with a fine diamond and polished with CeramiPro Dialite polishers (Brasseler USA).
•The abutment teeth were cleansed and isolated from moisture. Cementation of the crowns was started from both central incisors to avoid misalignment of the midline. Maxcem (Kerr), a self-etching, self-adhesive, self-mixing resin cement, was used for permanent cementation of the all-ceramic crowns. Excess cement was removed with an explorer and dental floss. The patient was instructed on post-cementation maintenance and was scheduled for a 2-week postoperative appointment prior to being dismissed.
•In the postoperative appointment, the patient had shown significant improvement in her oral hygiene maintenance, and the 6 In-Ceram Alumina all-ceramic crowns provided an excellent aesthetic result as well as good function (Figures 14 to 17).
It has always been a daunting challenge for clinicians to satisfy patients' aesthetic demands, maintain quality, reduce costs, and shorten turnaround time of dental restorations. High-tech CAD/CAM technology is the key that allows dentists to meet these demands. This article has discussed the clinical applications of the TDS dental CAD/ CAM system, a laboratory CAD/CAM system.
Apart from fabricating dental restorations, the system also offers a total solution for dental implant care from surgical planning, surgical template production, and provisional implant restoration fabrication, to permanent restorations. TDS Implant Smart (Pou Yuen Technology) is an implant surgical planning system that intelligently integrates CT scan data and computer graphics. Using CAD/CAM-fabricated surgical templates and CAD/CAM-manufactured implant prostheses, clinicians can provide implant care efficiently and cost-effectively.
In the near future, researchers and developers will continue to develop new CAD/ CAM technologies and materials that will enable even more remarkable applications in dentistry.
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Disclosure: Dr. Lee serves as director of research and development for U-Best Dental Technology at Anaheim, Calif. U-Best Dental Technology of USA and Pou Yuen Technology of Taiwan are both subsidiaries of International Pou Chen Group.
Disclosure: Dr. Yau serves as a consultant for the Dental Technology Department, Pou Yuen Technology Co of International Pou Chen Group.
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