Inside Dental Technology
February 2012, Volume 3, Issue 2
Published by AEGIS Communications
CAD/CAM Milling Units
Narrowing down your choices to find the most appropriate technology for your laboratory.
By John Orfanidis, CDT
The last 25 years of dental technology have dramatically changed the landscape of manufacturing restorations. From the days of Sirona’s CEREC® 1 and the first chairside shipments in 1987 to VITA’s Celay® copy-milling system and today’s continuous 5-axis milling machines, the transition from analog to digital processes has significantly impacted the way dental technologists approach and fabricate a case. The advancement in machines and materials as well as sophisticated software processes allows technologists to automatically place teeth, detect the margins, and automate occlusion. These are merely tools that help dental professionals manufacture dental prosthetics with more consistency and accuracy.
Milling technology has been used in many other fields to streamline manufacturing processes and improve the quality, consistency, and accuracy of the end product. The first automated milling machines for dentistry were large and very expensive. Today, those large, room-filling behemoths of yesterday have been replaced with milling machines that can fit on a desktop.
However, the output devices available today are only as good as the data they receive. Integral to the manufacturing process is a 3D scanner to digitize the physical model, CAD (computer-aided design) software to virtually design, form, and shape the restoration, and, lastly, an output device such as a 3-, 4-, or 5-axis milling unit, 3D printer, or SLS (selective laser sinter) sintering unit. Substructures and full-contour products can be produced in wax for the analog lost-wax casting process, directly machined in hardened materials such as leucite glass and lithium disilicate, or milled from materials such as zirconia that need to be fired to achieve the physical properties necessary for final fabrication.
Practically every dental company offers some type of CAD/CAM system. New companies without much dental experience are entering this arena with more to come. The numbers of systems on the market present a problem for large and small laboratories that are still deciding which system to purchase and from which manufacturer they want to work with. About 10 years ago, the choices were few and decisions were much easier. The handful of dental companies that had spent millions of dollars developing automated processes for the manufacture of crowns and bridges charged a premium for the technology. They also produced advanced materials that were locked in or “closed” to their proprietary systems. Today, laboratories looking to purchase a milling system also have the option to buy “open” systems that allow laboratories the freedom to choose from a broad spectrum of milling material suppliers and gives them the ability to upgrade to new materials as they enter the marketplace.
There are criteria to take into consideration if and when purchasing a milling unit. Laboratories need to focus their attention on versatility, price, and production output. Also to be considered is the technical support available from the manufacturer and detailed information about the consumables, whether those are milling materials or replacement parts such as milling burs.
There are many milling machines on the market that can perform a variety of different tasks but they are not for everyone. Some systems, particularly those sold as complete systems that include the scanner, design software, and milling unit, are optimized to work in an integrated fashion so that the user does not have to fine-tune each component to obtain the desired milled fit. There are also milling machines and components that can be purchased as stand-alone units but need work to dial in the accuracy and detail of the fitted end product. Today, most of these milling units are nearing “plug and play” operation but typically need some sort of tweaking by the customer.
For many years, 3- and 4-axis milling had been the industry standard for two reasons. The first was that dental work rarely needed milled structures with undercuts, and second was that 5-axis machines were too big and expensive. Today, 5-axis machines are much smaller and more affordable. The surface quality of the units milled in a 5-axis simultaneous milling machine is much better and allows for better detail and contours. However, the downside to producing greater detail and a better surface finish is that it takes longer to produce the final product. Milling, or subtractive production, also is a wasteful process. The author weighed out a single-unit, partially sintered milling block at 10 g. After milling, the final milled unit weighed a mere 0.3 g, which represents 97% waste. Currently, milling technology is the only way to fabricate zirconia-based restorations, but that may change. Other considerations that add cost to producing a final product with milling technology are tooling wear (burs) and the liquids and/or filters for vacuum systems. These all add cost to the final product.
Digital dentistry is the future of our profession. The driving force in the operatory will be an educated patient base demanding a digital alternative to conventional impression-taking techniques and materials. As more dentists understand the benefits of digital tools and processes and the cost of the technology drops, digitization will progress even faster. The driving force in the dental laboratory has been the rising cost of labor, the challenge of skilled labor resources, and competition from overseas. Emerging CAD/CAM technologies hold promise to help our industry become even more productive and competitive in this open market. Technologists must recognize these driving forces, envision the future, and navigate through the web of CAD/CAM systems to prepare their businesses to better accommodate the expectations of patients and clients for restorations that exhibit the amazing detail, consistency, and accuracy that this technology offers.
About the Author
John Orfanidis is the director of CAD/CAM technology in the Prosthodontics Department at Tufts University.