November/December 2011, Volume 32, Issue 4
Published by AEGIS Communications
CAD/CAM: Enhancing Productivity through Automation
There have been numerous articles written on intraoral digital impression systems, including some by this author.1-3 Information has focused on the differences in scanning systems, accuracy, and comparisons to traditional impression systems such as polyvinylsiloxane (PVS) or polyether. Two current systems (CEREC®, Sirona Dental Systems Inc., www.sirona.com; E4D, D4D Technologies, www.e4dsky.com) allow the practitioner to design and create final restorations in the office using simple software and small milling units. Still, many practitioners prefer to send their impressions to “traditional” dental laboratories and also often request materials beyond the current scope of in-office milling systems.
These two systems as well as other intraoral systems (iTeroTM, Align Technology, Inc., formerly Cadent, Inc., www.cadentinc.com; LavaTMChairside Oral Scanner C.O.S., 3M ESPE, www.3MESPE.com; IOS FastScan®, IOS Technologies, Inc., www.ios3d.com) allow the practitioner to “export” digital files to a dental laboratory for the design and fabrication of the restorations. With current technology, not only can crowns, inlays/onlays, and bridges be created, but also partial denture frames, implant bars, as well as some orthodontic appliances.4 In addition, laboratories are beginning to digitize traditional impressions and models, allowing the latest CAD/CAM technologies to be used. The days of model-makers and waxers in the dental laboratories appear to be numbered.
Let’s examine what happens now when an impression, digital or traditional, or a model is sent to the dental laboratory.
Step One—the Impression
If a digital impression is sent to the laboratory, the file must be in a form that the lab’s software can “read.” Some systems produce a generic file (also called an “open source” or STL file) while others require the laboratory to have proprietary software to read and translate the files to models. In a proprietary situation, the dentist must inquire as to which laboratories can accept the scan. If the dentist sends a traditional impression, the laboratory can either scan it, or actually pour a model and scan that (Figure 1). Two current popular systems that laboratories are using for this purpose come from 3Shape (www.3shape.com) and Dental Wings (www.dental-wings.com). Both of these companies are also marketing smaller versions of these scanners that could be used in the dental office, which will scan both impressions and models.
There is an instant advantage to sending a digital file to the laboratory—the file arrives almost instantaneously. This reduces turnaround time by a day or two. In some situations, the lab can evaluate the images immediately and talk to the dentist before the patient leaves the treatment room. Also, there is no shipping cost or risk of losing a case in transit.
In the situation where an intraoral file is sent, the doctor has already checked the impression for accuracy, occlusal clearance, margin, and contact locations, so no last minute calls from the lab are needed to bring the patient back in. Scanning an impression or model in the office can still have some imperfections, but these are known before the office hits the “send” button to the laboratory. This is a “win-win” situation for the dentist and the lab, and is also an indirect return on investment of digital impressioning.
Step Two—Creating the Restoration
Once the model is digitized, the technician examines the case on screen. The actual process at this point is quite similar to the system that has been used all along but the tools are quite different. A mouse, track ball, or in one case a “haptic” joystick (Sensable Technologies, www.sensabledental.com) is used to draw on the screen to create the restorations. There is a wide variety of software, many with familiar “drop-down” menus, that place (draw) a restoration or groups of restorations in specified locations on the model on the screen. For those with in-office milling centers, CEREC and E4D systems propose an ideal restoration on the screen for a crown, inlay, or veneer using “intelligent” designs as well as clones of the original tooth form or, in some cases, stock libraries.
The technician now “waxes” the restoration on the screen and makes modifications with software tools. Sophisticated virtual articulators (Figure 2) allow the technician to move the upper and lower models on the screen into precise excursions and even set the articulator condyles to parameters obtained from the dentists’ instructions, facebows, etc. At this point, depending on the materials chosen, the technician can send the design to a milling unit or to a unit that will create a castable wax-like pattern. In some situations, there are large blocks of metal, including titanium, that can be milled into a precise duplicate of the screen design. Gold itself, although certainly millable, becomes impractical because the waste filings of this expensive metal become cost prohibitive. Some partial frames and bars can also be fabricated using this type of milling system, however there is an entire technology arena—stereolithography (SLA)—that allows materials, including metals, to be “printed.”
Many industries use these processes and employ machinery from a company called 3D Systems, Inc. (www.3dsystems.com), which has now spun off a dental division (www.toptobottomdental.com). Another company active in this area is Objet Corporation (www.objet.com) in Israel, which prints a large array of products for many industries including dentistry.5 Credit for the groundwork in this area of technology can be attributed to a brilliant woman in the industry, Ping Fu, who co-founded Geomagic (www.geomagic.com), a provider of 3-dimensional (3-D) software for creating digital models of physical objects.6 This technology allows the technician to easily manipulate the design and move the patterns around, as the wax is continuously in a flexible state.
If a ceramic or metal coping was made, and a ceramist has to build porcelain, a model is necessary. However, this model is not stone; it will be created from the digital scan either by printing (SLA) or milling from a block of a hard acrylic material. The technician marks the margins and defines which teeth will be dies, and the computer handles the rest. Dies are ditched and models are sectioned in a much more precise pattern than a sawblade through plaster. These dies fit closely together like a jigsaw puzzle and do not wiggle. Many practitioners have seen dies, especially in the most distal tooth, in an arch that can be moved slightly, sometimes causing tighter contacts than anticipated. The other important feature of these models is that they are not subject to chipping or scraping as the restoration is placed on and off during fabrication. This leads to accurate margins and contacts.
Restorations that are designed and created totally by computers do not need models. These include restorations that are milled from blocks of metal or ceramic as well as printed restorations. Note that it is now possible for a CAD/CAM machine to mill a coping or bridge frame and then mill the ceramic covering. The two are put together like a puzzle with either cement or a low-heat fusion system. Some dentists are surprised when they realize that they will be receiving a restoration from the dental laboratory without a model. Although in most situations dentists never use the model, it serves as a “security blanket” to many who have been receiving them over the years.
In speaking with James R. Glidewell, CDT, CEO of Glidewell Dental Laboratories (www.glidewelldental.com) (July 2, 2011), his company has put a tremendous effort into digitizing its laboratory, which he says will save money for the lab and the dentist. Glidewell is confident that these CAD/CAM restorations will also have a better and more consistent fit, thus enabling shorter visits for insertion of cases (an advantage for the dentist) and fewer remakes (an advantage for the laboratory). In addition, Glidewell Laboratories recently introduced a new intraoral scanner (IOS FastScan), designed to streamline workflow and thereby enable lab customers to realize substantial savings. Practitioners who have been using CEREC or E4D systems already understand this model-less paradigm. These offices are also realizing an even more rapid delivery of the restoration—which is immediate. Certainly, as the export of files to laboratories becomes more common and the workflow more streamlined, turnaround will be faster.
Cadent Inc. (www.cadentinc.com) has a digital orthodontics process called OrthoCad IQTM, which allows the orthodontist to send vinyl polysiloxane (VPS) or PVS impressions to Cadent, which scans them and creates virtual models. The software allows the orthodontist with Cadent to arrange brackets on the computer screen and send this information back to the practitioner without ever pouring a model. This system assists the dentist in bracket placement on the digital models and then creates a placement guide, which looks like a clear aligner with places for the various brackets. All of the teeth are etched and prepared at once, and the guide is seated with the brackets in place and then light-cured through the clear material, saving significant time and increasing the accuracy of the bracket locations. These digital models can be retrieved in seconds and eliminate the need for orthodontists to have shelves full of stone models. If a physical model is desired, it can be ordered from Cadent’s OrthoCadTM.
In recent years, Align Technology, Inc. has brought Invisalign® into the marketplace. The Invisalign process has used digital models from the outset and has constantly employed updated technology. With its recent acquisition of Cadent, Align Technology now not only has years of experience with orthodontic models, but can use Cadent iTeroTM intraoral scanning to deliver a digital scan, thereby eliminating VPS/PVS impressions and thus reducing impression errors. The increased accuracy of, for example, interproximal areas creates better fitting aligners. It also allows a 48-hour turnaround for the dentist to obtain a ClinCheck® treatment plan. In addition, Align Technology can now print the aligners, significantly reducing turnaround time. This process used to include pouring models, using vacuum forming, and finishing for many models.
The practitioner has to be well aware of this laboratory aspect in order to properly treatment-plan and deliver cases. It is important to have a two-way relationship between the laboratory and the doctor as well as other relationships with manufacturers and software companies. There are many practitioners who currently pour their own models, ditch their own dies, and articulate them before sending them to the lab. This can still be done in the office on a computer screen, but the practitioner has to be well versed in the CAD/CAM software. The benefit here is that there will not be a long lag time between design and input from the lab as these electronic files are sent instantly. Some companies offer services that allow remote access from the lab (or for E4D users, S.O.S. Support on Sight remote support) to the dentist’s office computer, giving instant feedback and once again shortening the time from the patient’s appointment to the final delivery of the case.
Due to rapid changes in hardware, software, and devices, current practitioners must continue to read, listen, and take up-to-date continuing education (CE) courses to keep up with technology. In the end it is the patient who is the winner, with better and more efficient treatment.
The author would like to thank Eli Ganon for his help in gathering background material for this article, including up-to-date information on digital dentistry.
1. Koenigsberg AC, Feuerstein P. Digital update. Inside Dentistry. 2011;7(3):92-94.
2. Feuerstein P. New changes in CAD/CAM: Part 1. Inside Dentistry. 2007;3(2):84-86.
3. Feuerstein P. New changes in CAD/CAM: Part 2. Inside Dentistry. 2007;3(3):82-86.
4. New Dental 3D System Scans Oral Cavity. Dental Health Magazine. www.http://worldental.org/dental-news/new-dental-3d-system-scans-oral-cavity/767June 8, 2009. . Accessed September 26, 2011.
5. Cohen, A. Future of Dentistry: 3D Printing. Dental Health Magazine. January 26, 2010. www.http://worldental.org/dental-news/future-of-dentistry-3d-printing/1053Accessed September 26, 2011.
6. Brant J. Entrepreneur of the Year: Ping Fu. Inc. Magazine. December 1, 2005.www.inc.com/magazine/20051201/ping-fu.html. Accessed September 26, 2011.
About the Author
Paul Feuerstein, DMD
North Billerica, Massachusetts