For more on this topic, go to www.dentaleconomics.com and search using the following key words: CAD/CAM, crown and bridge, "computerized dentistry," Feuerstein.
by Paul Feurstein, DMD, Technology Editor, Dental Economics
Computer-Aided Design and Computer-Aided Manu-facturing (CAD/CAM) are terms that have invaded our practices during the past few years. Dental labs are bombarding our mailboxes with information about CAD crowns and bridges with a confusing array of products and claims. Higher strength and higher accuracy are among these marketing terms. A few companies are promising us the end of impression material while others promote crowns and even a full set of teeth in one visit. Two new systems in the marketplace look like intraoral cameras and promise to deliver a digital impression that can be sent to the lab via the Internet. I hope DHL and FedEx are taking heed!
There are many lab systems that help design and create copings and final restorations out of ceramics as well as metals. Zirconia is a popular material that comes in several varieties, in shades of white or yellow. When machined from blocks, their strength and accuracy allow these materials to be used as copings and bridge substructures without metal. Their lack of "gray lines" is only one of many advantages. Some of the CAD/CAM systems can create completed restorations using these materials, some from a single block, while others use two types — coping and tooth material that can be fused together. Other lab systems can cut from blocks of titanium, which create strong, thin frameworks out of one piece of metal, which avoids soldered connections and casting porosities. Another system, called STL (Stereolithography) and RP/RM (Rapid Prototyping/Rapid Manufacturing), can, in essence, "print" a coping using particles of zirconia, ceramic, and metals, including gold. This process is similar to a laser printer placing powdered toner on a sheet of paper. Imagine the toner being layered by the printer"s head passing over the paper again and again. These new systems work like that and, with each layer, a laser melts/welds the particles together. The days of wax and cast might be numbered.
The copings and crowns can also be designed on a computer screen. Most systems supply the programs with a library of standard coping and tooth designs. The technician, now using a mouse instead of wax and carving instruments, can tweak the results and do a virtual try-in before hitting the "finish" button. A new company, SensAble, allows the technician to wax up a crown or partial framework using a mouse-like pen that can actually "feel" the model using force feedback technology like that used in some video games. The CNC (computer numerical control) machines take the place of the casting rings.
Workin' it in the real world
I had an opportunity to speak with Jim Glidewell, who owns a large dental lab bearing his name. Jim and his company have made an enormous investment in machines that do many of the mundane tasks of the typical lab technician. The CAD/CAM machinery allows a "technician" to design a crown quickly and, instead of going off to be waxed, cast, pressed, or built, a push of a button completes the task. Over time, says Mr. Glidewell, this will cut labor costs and reduce the cost of crowns. Of course, there is a multimillion-dollar investment to be recouped, although the volume of a large lab should make the economics work.
One important issue still remains: the lab needs an accurate impression to get these new prosthetic results. If the CAD crown is to be made, the model or impression must be scanned, which is only as accurate at the initial impression. Dr. Gordon Christensen published an article in JADA in 2005 which described inadequacies in impressions received by labs. Many of the issues relate to poor margin clarity, sometimes due to less-than-perfect retraction or exposure. Others have to do with technique problems, such as allowing impression materials to set too fast or too slow, which causes steps, delamination, and other problems.
The first real CAD/CAM entries into the dental marketplace were Procera by Nobel Biocare on the lab side, and CEREC by Sirona on the dentist side. Procera copings required the lab to send models out to be scanned, where the Procera lab fabricated a coping. This was sent back to the initial lab for hand building of porcelain or other compatible materials over the computer-generated coping. Eventually, labs were able to purchase their own scanners and simply export the files to the Procera lab, saving time and of course, shipping one way. CEREC took a different approach and put the scanner in the hands of the dentist for use directly in the mouth. The restoration can then be designed and fabricated in the office. The product has evolved to its current state with more powerful computers and software, simplifying and speeding up the process while increasing accuracy.
More players in the field
The CEREC concept of in-office scanning and milling has recently acquired a competitor. Sullivan Schein has finally released its E4D system. It uses a laser in the wand and requires no powdering. The software is robust and has a few unique features (for now) like the prep review in the ICE mode, which allows the clinician to design the restoration on an actual photo image of the teeth as opposed to a computer rendering. Several other features distinguish this product from CEREC, however be assured that each company is watching the other. This can only help the end user, as competition will take these products to even higher levels.
Many practitioners availed themselves of CEREC, but in some situations hoped for a method for a lab to help with finishing, shading, and polishing the restoration. Some offices spend time with staining and glazing ovens and can create remarkable restorations, but many do not want to expend that extra energy. That day has arrived with CEREC Connect, a process that allows the practitioner to scan the tooth and send the file via the Internet to a CEREC Connect lab.
This, of course, does not deliver the case in one visit, but some practitioners are willing to give that up for a slightly higher quality and esthetic restoration, as well as not having to "deal with" designing, manufacturing, and finishing the case in the office.
One of the market conditions that may have pushed this idea was the introduction of Cadent's iTero. This new system gives the practitioner an acquisition unit, conceptually similar to an intraoral camera, that produces a truly digital impression that can be easily assessed prior to "shipping" it to the lab. The sophisticated software allows the dentist to review the impression and preparation, some by eye and some with the aid of software. Information such as incomplete margins or insufficient occlusal clearance is offered to the practitioner, which allows an opportunity to modify the preparation or retraction before sending it to the lab with such common instructions as "Do the best you can." Re-prepping and "re-impressing" is not as big of an issue as taking a new scan, which is quick and doesn't require patients to have the "stuff" put in their mouths once again. Once the impression is accepted, it is sent off to a Cadent authorized lab for fabrication of the restoration. The system generates enough information for the lab to create a physical model using CAM. Once the model is made, a restoration can be made using traditional processes. An advantage of the models is that the computer makes them out of a very hard acrylic material.
When the technician builds the contacts, there is no abrasion of the adjacent teeth that can sometimes be an issue with plaster casts, causing cases to come back with tight contacts. iTero also gives an option to have a coping made by their lab using a CAD/CAM machine. This creates a very accurate internal fit, and it will only be a matter of time before these labs can finish the crowns with computerized processes.
Experiencing new benefits
Since these restorations are so accurate, the cases delivered require less chair time at the seating appointment, and certainly fewer remakes. Dr. Virginia Plaisted of Delmar, N.Y., has been using this system for more than 10 months. Her experience has been more than enthusiastic — she's done more than 250 units of crowns without taking a traditional impression. Her real thrill is the seating appointments, where there have been no open contacts, slight adjustments, and significantly reduced chair time. The word "remake" no longer exists in her vocabulary.
Dr. Gary Henkel of Horsham, Pa., has been working with Cadent for about four years and has incorporated the iTero into his practice. Although a "power user," he has some valid points on the ROI for the dentist:
- Accuracy is much greater, yielding a more predictable fit and a low rate of remakes.
- There is no impression material which is in the patient's favor, especially with gaggers, and thus no mixing, no mess, and easier asepsis — the impression obviously does not have to be disinfected.
- Seeing the preparations on the screen magnifies the work and alerts the dentist about imperfections that might need correction.
- There are analytical tools, including those that evaluate interocclusal distance and axial reduction.
- There are real cost savings associated with the absence of trays, impression material, and even shipping and delivery costs.
- And finally there is the "wow" factor that puts a practice in the latest high-tech arena that can lead to public media marketing.
Dr. Henkel published a comprehensive review of this system last August.
Video streams now playing
In the meantime, a group in Massachusetts called Brontes Technologies were working with a team of engineers on an idea that came from a couple of MIT professors. Their intraoral scanner uses a video stream as opposed to CEREC's and Cadent's multiple still photos or E4D's laser. They were acquired by 3M in October of 2006, added a larger team of experienced dental developers, and have recently released the new (renamed) product called LAVA COS (Chairside Oral Scanner). This system also allows the files to be exported to a processing center that creates extremely accurate models using STL. These models, like iTero, can be sent to any lab to create restorations in a traditional manner. The extra bonus is that the files can be exported directly to a LAVA milling machine and can create as perfect a coping as possible without a model.
Of course, LAVA only creates the copings and substructures; the ultimate restoration still has to be finished on the model. Although the COS is branded LAVA, it is not a requirement to use that product for the copings. It is, in this case, 3M using a familiar brand name to keep this unit in a group. A more extensive review is forthcoming.
On the horizon
There are a couple of other intraoral scanners in the works. One is in development in Israel by Densys3D, however as of press time they did not have a unit ready for public display. Also, Jim Glidewell is watching this all very carefully and has hinted that he may have a scanner up his sleeve. Although competitive, it is important to note that all of these companies are working together toward a common goal. The technology has been verified and, no matter which system you use, the practitioner can be assured that the scan acquired is as accurate — and probably more accurate — than the traditional impressions used today.
There is, however, a common pitfall. Since they all use an optical system of some sort, the impression can only "see" what the eye can see. Retraction and margin exposure is critical, as is the absence of fluid. At least at this time, the systems cannot easily distinguish between hard and soft tissue, or detect fluid in the sulcus or on the prep.
The people processing the scans at 3M or Cadent can distinguish some of these artifacts, but in order for them to be efficient, the practitioner has to deliver a close-to-perfect situation. Also, there seems to be difficulty in reading long subgingival margins, despite good retraction. Light-body impression material can seep into these crevices with low surface tension in areas where the optics cannot see. Many practitioners have changed their prep design and location of the margins when using these scanners.
On the lab side, there is also an explosion of manufacturing systems. Procera (NobelBiocare) and LAVA (3M/ESPE) have been mentioned here, but many others exist and still more are coming. An incomplete list is: KaVo (Everest), Dentsply (Cercon), Sirona (InLab), Etkon/Straumann (Etkon), Wieland (Zeno), Hint-Els (DentaCad), CeraSystems (CeraSys), Bego (Medifacturing), XPdent (Wol-Ceram), Katana/Noritake (Katana), TDS (Ubest), 3D Systems (3Shape), and Renishaw (Incise). On the RP/RM side, there are 3D systems, Imagen, EOS, and Phenix systems. Atlantis, now part of AstraTech, specializes in CAD/CAM implant abutments. These systems vary in size, cost, and features, which is agonizing to a lab with a limited budget that wants to get into this arena. Luckily there are enterprising larger labs that purchase one or more of these systems and become resources for smaller labs, i.e., subcontractors. Thus, your local "mom and pop" lab can still give you their artistry on a substructure that was made elsewhere.
Geomagic — behind the scenes
One industry note — many of these systems are based on software created by a company called Geomagic. This unique software is used in many industries around the world and is the "engine" behind many dental CAD systems. For a complete list, go to geomagic.com. While you are there, read the profile of the founder, the amazing Ping Fu. There is a link to an article in Inc. magazine on their Web site in the "management team" section, where it tells about this "Entrepreneur Of The Year." Her story is an eye opener.
This is an exciting time in dentistry and will be cause to reflect on how processes were taught to you in dental school. The younger graduates, who have grown up with XBox and Wii, are used to seeing these 3-D renderings and will probably have an easier time adapting these concepts in their dental practices. Great expenditures are being made by companies and labs, large and small, to get this technology to the forefront. Don't blink or you might miss it!
References available upon request.
Dr. Paul Feuerstein is the technology editor of Dental Economics®. He installed one of dentistry's first computers in 1978. For more than 20 years, he has taught technology courses. Dr. Feuerstein is a mainstay at technology sessions, including annual appearances at the Yankee Dental Congress, and he is an ADA seminar series speaker. A general practitioner with an office in North Billerica, Mass., since 1973, Dr. Feuerstein maintains a Web site at www.computersindentistry.com. Reach him at [email protected].