Written by Thomas Grimes, DDS, and Tom Neiting, CDT Thursday, 08 July 2010 15:21
“Digital dentistry” is a fairly recent term in the world of dentistry. It is a necessary phrase in the dental lexicon, as many of the tools in the dental professional’s armamentarium are either run by computers or contain microchips that help make them work.
In terms of overall significance to the way dentists practice, as well as in terms of widespread use and acceptance by dental professionals worldwide, digital radiography is usually the first “new” digital dental technology to come to mind. This is most likely because it came to market more than 15 years ago as the first major shift from doing something the “old way” (radiography using film; ie, analog process) to doing it in an entirely new, faster, better, more efficient, and more economical way: digitally!
Today, thanks to CAD/CAM in the dental operatory, the advent of digital impressions is upon us. Just as digital radiography gained acceptance and praise by dental professionals worldwide, chairside CAD/CAM restoration systems (such as the CEREC AC [Sirona Dental Systems] and E4D [D4D Technologies]), have similarly become “mainstream” technologies in many dental offices throughout the world. Similarly, CAD/CAM restoration systems have gained major inroads into dental laboratories as well. It was only a matter of time before these 2 digital technologies—in-office CAD/CAM and in-laboratory—became “connected” to open up new restorative possibilities between dentists and laboratories. (Current examples include: CEREC Connect/CEREC inLab [Sirona Dental Systems] and E4D Labworks [D4D Technologies].) The Internet is the link that binds these 2 together. Web sites, or Web portals, such as cerecconnect.com, allow the transmission of digital impressions from dental office to dental lab instantaneously as a digital file, replacing the need for impression materials.
Diagnosis and Treatment Plan
A 70-year-old patient presented with an existing removable bridge on teeth Nos. 13 to 15. The patient did not like the look and feel of the bridge, especially the metal connectors.
Treatment options were discussed, and the patient ultimately chose a 3-unit permanent fixed bridge. This bridge would be comprised of a zirconia substructure veneered with an aesthetic ceramic material. This kind of metal-free restoration provides proven clinical and procedural benefits, such as excellent biocompatibility, the high strength necessary for posteriors, and a streamlined and efficient process.
The patient was happy to know that there would be no need for impression trays; instead, the impressions in our case were to be captured digitally with the CEREC AC acquisition unit. This information would then be provided to the lab electronically using CEREC Connect, which connects CEREC dental offices and inLab dental laboratories.
First, shade information was taken from the neighboring teeth to establish the necessary color and value of the new all-ceramic bridge. Teeth Nos. 13 and 15 were conservatively prepared to accept the all-ceramic crowns that would serve as the bridge to support the pontic in the space where tooth No. 14 once was (Figure 1). Accurate tooth preparation is key to a successful restorative outcome, as well as to successful scanning with the CEREC AC Bluecam optical scanner, which uses a blue LED. For best results, the Bluecam optical scanner should be positioned over the long axis of the preparation. At this angle, the operator should be able to view the entire preparation. Preparations can be either designed using a shoulder or a soft chamfer margin.
After the teeth were prepared, a light coating of OptiSpray opaquing medium was applied to enhance the quality of the digital impression. The digital impression improves patient comfort, because it will not subject the patient to the potential discomfort of conventional impression trays and materials. Furthermore, a digital impression—which is a real-life image—can be immediately reviewed for quality on screen, while the patient is in the chair. After the digital impression of the preparation is captured (Figure 2), the dentist may elect to take control and indicate the margins, or simply submit the case and allow the lab to do it. Next, 2 more digital scans were done to capture the opposing dentition and buccal bite.
Sending the Digital Files to the Dental Laboratory
Digital impressions, opposing arch scans, and bite registrations are quickly and easily transmitted to the dentist’s laboratory via CEREC Connect (Figure 3). The dentist fills out the online prescription form, entering pertinent information such as the patient’s age, teeth numbers, indication, material type, and desired restoration shade (Figure 4). Once the prescription data is entered, additional information or instructions may be added, as well as digital photos or files, such as those produced by digital x-rays or shade-taking devices. In order to electronically sign the digital prescription, the dentist enters his license number and password. At the touch of the “submit” button, all of these are sent immediately to the receiving laboratory (Figure 5). The CEREC Connect Web site acts as a portal or gateway that links CEREC dentists and inLab laboratories—allowing them to communicate in real time, when necessary, to view digital impressions and prescription data together, make suggestions or recommendations about the parameters of the case, and ensure that both have a firm understanding of the case and desired outcome before the case proceeds to the physical model stage. After all data is sent to the lab, model fabrication and restoration design begin.
Restoration Design and Fabrication
The digital impression is received at the laboratory and the design process begins. Unlike conventional impressions, digital impressions do not require infection control or preparatory work and can move straight to production.
First, a work ticket (a “Digital Rx”) with the case information is printed out; this will accompany the case throughout the lab phase. Because this case was a 3-unit fixed bridge, a physical working model of the impression, as well as of the opposing dentition (half-arch), was deemed necessary to ensure an accurate and precise occlusion and functional bite. To obtain the models, the digital impression and other files were forwarded to Sirona’s physical model fabrication center, located in Charlotte, NC. At the center, the data is transformed into a working model using a state-of-the-art, 3-dimensional (3-D), rapid-prototyping system (Figure 6). This system can best be thought of as a printer that produces actual 3-D models. It works through the use of a process called stereo lithography, in which a laser is fired into a special heat-activated resin (plastic) material. The heat generated by the laser hardens the resin into the exact shape of the digital model. The final model is “built” by an additive process: layer by layer, the resin is hardened into final form. Once completely built, the model or models are returned to the laboratory. Unlike conventional models, these digitally fabricated models are dimensionally stable and are an exact representation of the situation in the patient’s mouth.
Upon receipt of the models back at the dental laboratory (Figure 7), design and fabrication of the restoration can begin. In this case, a 3-unit bridge was designed using the inLab system’s 3-D design software. The original digital impression was brought up on screen, and the bridge was designed using the inLab system’s software tools. The dental laboratory technician has total control over all aspects of the restoration design, including wall and interconnector thicknesses. The technician can quickly and easily design the framework using special software tools developed specifically to facilitate rapid yet precise design of both understructures and fully-contoured restorations. The software provides the technician with the necessary tools to adequately support the veneering porcelain while maintaining total control of the ultimate outcome.
Once satisfied with the restoration, the dental technician has the inLab system mill the design out of a single solid block of all-ceramic material. There are many material options to choose from; in this case, zirconia oxide was chosen due to its high strength and aesthetic properties that ideally match the functional and aesthetic demands of this case. After milling, the restoration is sintered, a process that brings the material to full strength. It is then finally fitted to the model and the fit was found to be perfect (Figure 8)—a passive, yet snug, correct fit (Figure 9).
Next, porcelain buildup, characterization, and glazing were achieved. The finalized restoration was tried in on the polymer model. The occlusion was perfect, as demonstrated on the articulator (Figure 10).
Received at the dentist’s office on the date specified on the electronic prescription, the finished restoration was ready to be tried-in and seated in the patient’s mouth. At try-in, the bridge was found to fit just as perfectly as it did on the polymer model at the laboratory. The restoration was permanently seated using a conventional cementing process. The bridge looked great and both patient and doctor were very pleased with the clinical and aesthetic results (Figure 11).
Digital impressions, buccal bite registrations, and scans of opposing dentition provide excellent means of obtaining all the pertinent physical information about a patient’s current dental situation without having to use conventional impression trays and materials. Digital scans are more accurate because they are not subject to voids, tears, bubbles, or shrinkage, and do not require disinfection; they provide an actual “snapshot” of the patient’s oral situation without any distortion. Furthermore, digital impressions are far more comfortable for the patient and more accurate because the dentist can see the impression and review the real-life situation immediately. Likewise, if needed, corrections—or even an entirely new scan—can be made instantly. There are no dimensional changes of the impression or conventional model to worry about or make provisions for. Economically, digital impressions save money because there are no impression material costs and no outbound shipping costs.
This case demonstrates how digital dentistry can streamline, enhance, and improve the restorative process in several ways beneficial to all involved: patient, dentist, and laboratory owner.
Dr. Grimes is a general dentist who completed his undergraduate studies at Davidson College before earning his dental degree in 1988 from the University of North Carolina at Chapel Hill School of Dentistry. For more than 15 years, he has been providing patient care at Advanced Dentistry of Blakeney and Matthews. He was one of the first doctors in Charlotte to start utilizing the CEREC one-visit crowns and partial crown technology more than 11 years ago. Dr. Grimes is a member of the American Dental Association and the North Carolina Dental Association. He can be reached at (704) 845-1107.
Disclosure: Dr. Grimes has previously been a beta tester for CEREC but has received no financial compensation.
Mr. Nieting, a certified dental technician (CDT), started his career in 1972 as a dental technician trainee and worked for more than 35 years as a CDT and ceramist. He was the general manger of Lemke Dental Lab, a 50-person, full-service lab in Minnesota. He joined Sirona Dental Systems in Charlotte, NC, in 2006 as the technical marketing manager for Laboratory CAD/CAM. He is the co-founder of DENTATRUST, located in Charlotte, NC. He was the first CEREC inLab user and beta tester in North America and conducts CEREC advanced software trainings and lectures internationally. He can be reached by phone at (980) 355-0020.
Disclosure: Mr. Nieting acts as a beta tester for CEREC but does not receive any financial compensation.
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