Digital Impressions: Eliminating the Weak Link
Posted Apr 28, 2011 in Digital Dentistry
"Everybody knows impressions are the weak link in the restorative process. We've all been dreaming of the day when computers could take a more accurate impression, and now, that technology has arrived. Digital impressions are the wave of the future," says Laboratory Owner Dave Lampert. His lab, Town & Country Dental Studios, Freeport, New York, is one of the seven labs beta testing the Cadent Electronic Imaging Device, a digital impression-taking system that allows the dental team to fabricate PFM and all-ceramic restorations without a conventional impression. The design of the system builds upon Cadent, Inc.'s experience with its Orthocad™ service for orthodontists (see box at right) and has been in development for several years.
Here's how it works. The operatory components consist of a handheld scanner that connects to a hard drive and flat panel monitor housed on a mobile cart; the entire system is wireless. The dentist or assistant fills out a digital prescription indicating the type of restoration he wants to seat. The software guides him through a sequence of intraoral scans, including the occlusal view, adjacent and opposing teeth and a 90° buccal scan of the jaw. The entire scan sequence takes three to five minutes, about the same time as it takes a conventional impression tray to set.
Next, the operator selects the view icon and a highly magnified, 3-D rendition of the oral anatomy is displayed on the monitor. He can manipulate the view, add or remove the opposing jaw, or rotate the image to look at the finish line from every angle. There is also a color mapping feature that shows the amount of occlusal clearance; for instance, a bright red area indicates more reduction is needed in order for the ceramist to properly build up the porcelain. The dentist can take additional scans and re-prep if needed; no special prep or retraction techniques are required.
The CAD software image of cad software in use at the lab A screen shot of the CAD software in use at the laboratory.
The data is transmitted via high-speed Internet connection to Cadent's U.S. headquarters in Carlstadt, New Jersey, where a preliminary, digital design of the copings is created and then downloaded to a beta test laboratory. Using the CAD software, the lab analyzes the preliminary coping design, checking for areas of soft tissue impingement and margin lines. If necessary, the technician can call the dentist to discuss the case and both parties can look at the magnified, 3-D image simultaneously.
After the design is modified and/or approved, the lab uploads the data to Cadent's facility in Tel Aviv where milling machines produce models with removable dies from a special material and either wax copings are fabricated that can then be cast or pressed, or the dies can be scanned and then milled in other materials. The articulated working and opposing model or coping and check die are sent back to the laboratory where the fabrication process is completed.
Beta testing feedback
To date, about 900 cases have been fabricated at the beta test sites, including 15 dental practices, and users are excited about the technology. "We've fabricated about 60 PFM and all-ceramic units and the fit is as good, if not better, than what we could have achieved with conventional techniques. Plus, our clients love not having to put their patients through the uncomfortable impression-taking process," says Lampert. "This technology is changing the way we work with our dentists and how they work with their patients and this will benefit all of us."
Lab President Justan Koch, Artisan Dental Laboratory, Portland, Oregon, agrees. "This technology is win/win for everybody. The software's 3-D views provide doctors with instant feedback. The occlusal clearance mapping is especially helpful and makes it much easier for the lab because we don't have to make that difficult call to tell the dentist there isn't enough room or try to correct the problem by reducing the coping or trimming the opposing dentition. Impressions are without a doubt my number one headache and I predict our remakes will go down 75% with this product."
At one test site, Cadent is conducting controlled comparison studies in which the lab fabricates two restorations--one from the digital impression and one from the conventional impression--and shows both options to the dentist. Only the owner and Tim Mack, Cadent's vice president of business development, know which crown is which. "In 70% of the cases, dentists have preferred the crowns fabricated from the Cadent impression, saying they have better retention, marginal adaptation and less adjustment," says Mack.
Both Lampert and Koch tout the CAD software as being well designed and very user-friendly. "The learning curve wasn't much different from other CAD systems and, since we had prior experience, we were able to work with the system from day one," says Lampert.
Since the system is still in testing and development, Cadent and the test labs acknowledge that there are still a few bugs to be worked out. The turnaround time between the lab sending the data to Tel Aviv and getting back the model is currently two to two-and-a-half weeks. According to Mack, this time should be shortened significantly once the Carlstadt, New Jersey milling center is fully operational, probably by next month.
The weight and size of the handheld scanner is also an issue. "We're further miniaturizing the handheld scanner," says Mack. "The next generation should be a more manageable size and weight and we expect it to be ready for field testing next month." Cadent is aiming to have the system on the market in selected areas by the second quarter of 2006.
The development of the Cadent system
Founded in 1996, Cadent, Inc. entered the digital arena with Orthocad, a scanning system that enables orthodontists to create a digitized study model from a conventional impression, post it to the company's secure website and use the various 3-D information services, including digital model fabrication, virtual setup, indirect bonding and bracket placement.
Based on its experiences with that system, the company recognized the challenges of impression taking and the application that Orthocad could have on the fixed restorative side. It developed an electronic impression device (EID) for use by general practitioners and prosthodontists and, after testing the alpha unit for about 18 months, the company started beta testing in mid-2004.
In comparison to Sirona's Cerec 3 chairside CAD/CAM milling system that also has an optical impression-taking component, Cadent's business model includes the lab in the fabrication process: the lab still interprets the treatment plan, then digitally designs the copings and performs the porcelain buildup process.
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