July/August 2011, Volume 7, Issue 7
Published by AEGIS Communications
Computer-assisted design/computer-assisted machining (CAD/CAM) describes the computer/graphic workflow for digital imaging, software design, and milling of a restoration. CAD/CAM systems for the dental office not only record digital impressions intraorally, but the digital file is used to design and mill restorations in the office so they can be delivered in a single appointment. The CEREC AC (Sirona Dental Systems, www.sirona.com) and E4D System (D4D Technologies, www.e4d.com) are the two marketed in-office CAD/CAM systems. The CEREC AC unit also is capable of being used as a digital impression system and transmitting digital files to the dental laboratory through CEREC Connect for restoration fabrication.
Digital impression systems refer to computer-based intraoral cameras or scanners used to record a digital file of the dentition and soft tissues for viewing on a computer monitor or as a virtual model. Electronically transmitted for restoration fabrication, the dental laboratory can use the digital impression file to process working models, as well as use the file in a CAD/CAM process to fabricate the restoration. Any type of restoration—including cast gold and porcelain-fused-to-metal, but most commonly either zirconia or lithium disilicate—can be fabricated on the models. The most commonly known digital impression systems are the Lava™ C.O.S. Chairside Oral Scanner (3M ESPE, www.3mespe.com) and iTero™ (Cadent, www.cadentinc.com/itero).
Digital impressions are commonly recorded as .stl files. Although this may appear to be a universal file format, each manufacturer has a proprietary .stl file format that limits their universal application. When digital impression systems were first introduced, the .stl files from a specific digital impression system were limited to processing with a single proprietary system (ie, “closed architecture”). This forced dental laboratories to purchase computer design and milling units unique to a specific manufacturer’s digital impression system. More recently, companies have been willing to open the proprietary .stl files for import to other CAD/CAM systems common in dental laboratories. This is referred to as “open architecture” and allows dental laboratories more flexibility in accepting .stl files from a variety of systems, without needing multiple computer design stations and milling units. This also allows doctors more flexibility in selecting dental laboratories to work with, because more laboratories can accept a variety of digital impression files.
Both Lava COS and iTero have software features that provide immediate quantitative information about the amount of occlusal clearance for the cavity preparation. This type of immediate feedback maximizes the potential for avoiding insufficient occlusal clearance on cases, because the preparation can be modified and efficiently rescanned, rather than requiring the dental laboratory to work around the problem in the preparation. Virtual mounting of opposing quadrants or arches is predictable by using either bite registration or buccal imaging techniques. Efficiency and simplicity of design workflows have been improved for chairside systems.
Although digital impression systems are most commonly used for restoration fabrication, new applications of the digital impression files have been introduced. Align Technology, Inc., has acquired the iTero (Cadent) scanner, offering an opportunity to integrate the recorded digital impression file with Invisalign orthodontic treatment. The digital file is used for both case planning and implementing treatment.
Several digital impression systems have opened new applications for dental implant treatment. Doctors will be able to make a digital impression of a healing abutment or “scanning abutment” that will scan embedded codes on the occlusal surface of the abutment, as well as the surrounding soft tissue and adjacent dentition. These codes provide specific information to the design software for properly aligning the manufacturer’s implant within the virtual model. The full contour of the restoration, as well as the design of the supporting abutment, can be developed with the software.
The iTero scanner can be used to image scan bodies and import them to make 3i abutments. BIOMET 3i (www.biomet3i.com) announced a new collaboration with 3M ESPE that uses BIOMET 3i’s patented Encode® Impression System with the Lava™ C.O.S. to create intraoral impressions for custom abutments.
Evaluating the financial impact of moving to digital technology is always a challenge. Dental laboratories and doctors have developed new business models that encourage the implementation of digital technology. It was commonplace for a “click fee” to be charged for electronically transferring digital files to the dental laboratory. The click fees are no longer that prevalent. However, as the economy of time and effort of using digital technology has been realized, laboratories have started to offer discounts to doctors who transmit cases electronically instead of by mail. Other dental laboratories have started to offer volume discounts when doctors electronically transmit a specific number of cases within a month or quarter, furthering the financial savings for moving to digital technology.
Digital technology continues to evolve, and doctors should be mindful of the developments. New corporate partnerships, increased open architecture of digital systems, innovative clinical applications, and emerging business models continue to foster a strong development environment for the technology. Many doctors have made the move to digital dentistry, and there surely will be more to follow.
About the Author
Dennis J. Fasbinder, DDS
University of Michigan School of Dentistry
Ann Arbor, Michigan