Written by Todd R. Schoenbaum, DDS Monday, 13 February 2012 14:09
Without many in the profession taking notice, restorative dentistry is currently undergoing its most significant revolution since the introduction of adhesive dentistry; this is the digital revolution, and it is the beginning of the end for physical impression materials. Though digital impressions (starting with CEREC 1 [Sirona Dental Systems]) have been in the market for more than 25 years, it is only in the last 5 years that we have seen the development of significant competition. And with this has come a dramatic uptick in innovation and development for digital impression units and CAD/CAM devices.
Some clinicians may be quite happy with their current impression materials and see little reason to consider changing to digital impressions. And fortunately for them, the physical impression materials will continue to be available for quite some time. Like much of dentistry though, we (and our patients) have simply adapted to the annoyance and frustration that come with physical impression materials. Patients don't often complain about impressions and having to wear a provisional restoration because many do not know there is an alternative. Clinicians have come to expect that a cementation appointment requires 30 minutes or more, and that the prosthesis will often require adjustments. It is also difficult for us to consider switching away from an impression technique that we have worked so hard on perfecting. Those who do make the decision to switch from physical to digital impressions and CAD/CAM will inevitably have a learning curve to address, but there are significant benefits to gain in getting through it, particularly in terms of patient recruitment and retention.
|Figure 1. There are currently 4 digital impression/CAD/CAM units available in the United States (from left to right): Lava C.O.S. (3M ESPE), iTero (Cadent), E4D Sky (D4D Technologies), and CEREC AC Bluecam (Sirona Dental Systems).||Figure 2. The CEREC system is available with or without one of 2 CAD/CAM milling chambers; shown here is the MCXL unit.|
|Figure 3. The E4D has one optional CAD/CAM milling chamber.|
As of this writing, there are currently 4 digital impression devices available in the United States market (Table 1) (Figure 1). There are 3 more units that will likely be available for purchase in the first or second quarter of 2012. Digital impression devices are best understood as 2-component systems. One component is the digital impression unit (Figure 1); the other component is the CAD/CAM chamber (Figures 2 and 3). Currently, only 2 systems (E4D [D4D Technologies] and CEREC AC Bluecam [Sirona Dental Systems]) are available with an in-office milling chamber. The digital impression unit is placed chairside in the operatory and is used by the dentist or the chairside dental assistant to digitally scan the preparation (a digital "impression"). The CAD/CAM chamber is generally located in the office laboratory and is then used to mill the restoration. The systems are available in 2 configurations: as a stand-alone digital impression unit, or as a complete in-office CAD/CAM system that includes the digital impression unit and the CAD/CAM chamber (Table 2).
CURRENTLY AVAILABLE DIGITAL IMPRESSION UNITS (STAND-ALONE CONFIGURATION)
- Lava C.O.S. (3M ESPE)
- iTero (Cadent)
- CEREC AC Connect (Sirona Dental Systems)
- E4D Sky (D4D Technologies)
Digital impression units function as a digital replacement for physical impression materials (ie, vinyl polysiloxane [VPS]). The operator prepares the teeth to be treated (Figures 4 and 5), and manages the soft tissue much as would be done for a physical (ie, VPS) impression. Some of the systems (Lava C.O.S. and CEREC, for example) require the application of a contrasting powder before scanning. The digital impression unit is placed chairside in the operatory, where the screen can be seen by the operator. The operator then scans the prepared arch, the opposing arch and the bite using the intraoral wand (Figure 6) to take a series of digital images (iTero, E4D, CEREC) or a digital video (Lava C.O.S.). Each system uses a unique and proprietary technology to achieve the capture of the digital scan data, and each system requires a slightly different technique. The scan process takes an average user 3 to 4 minutes. Beginning users may find that they need a few minutes longer per scan as they learn how the technology operates.
All 4 devices are also capable of taking full-arch scans, as needed. In addition, most offer adaptors for use on all major articulator systems. No changes to preparation designs or preparation dimensions are needed. Most systems offer the unique advantage of being able to determine the exact occlusal clearance through the use of a digital "color map." This is a huge advantage over the traditional physical impression materials, where the exact amount of occlusal reduction cannot be accurately seen until after the case arrives at the dental laboratory and is made ready for fabrication of the restoration. Avoiding the need for a second preparation and impression appointment due to lack of occlusal clearance has obvious benefits for both the dentist and the patient.
|Figure 4. Failing restorations and edentulous site prior to preparation.||Figure 5. The fixed partial denture (FPD) preparations are completed.|
|Figure 6. Each system has a different approach to the imaging technology and, as a result, each wand has a different appearance and operates in a unique way.||Figure 7. The digital model allows the user to verify that all critical areas have been appropriately captured.|
|Figure 8. Most systems (the Lava C.O.S. is shown here) allow the user to check the preparations using high definition images equivalent to 20x magnification on an operating microscope.|
Following the scan, the clinician confirms that the preparation and other relevant areas on the digital model (Figures 7 and 8) have been accurately recorded, and that the occlusal clearance is appropriate for the material selected. Some systems allow the user to annotate the preparation scan to indicate the desired margin position in cases where the answer may not be obvious. Following the digital scanning process, provisional restorations are placed.
In the background, the digital impression unit is compiling the scan data and preparing it for export. Once ready, the data is sent through a wireless router to the appropriate model facility or laboratory. With the aid of a software program, a trained digital technician will digitally mark the margins, and then digitally ditch and trim the dies. The digital model is now ready to become a physical model. With most current systems, a physical model will be milled (iTero) or stereolithography printed (Lava C.O.S.) (Figures 9 and 10), from which technicians can work in much the same way they always have, but now with the accuracy and convenience of a more durable resin model. This model is then shipped to the clinician's dental laboratory of preference. The models will generally arrive at the laboratory within 3 days of the original scan. With this model, the technician can fabricate any type of restoration, from feldspathic porcelain to zirconia to gold. Alternatively, some of the systems now offer the laboratory the ability to mill the restoration directly from the digital data without the use of a physical model. This can be a bit unnerving for the clinician and technician who are accustomed to checking and adjusting the restoration on a physical model, though it does offer a significant savings in time and cost.
Once completed in the laboratory by the technician, the final restoration is delivered to the clinician (generally within about 2 weeks of preparation) for cementation (Figure 11). Most users report that the cementation procedure is dramatically shorted and more often adjustment-free as compared to their experiences with traditional physical impression materials.
The stand-alone digital impression units (iTero and Lava C.O.S.) are well-suited for the clinician who wants to bring digital technologies into the practice, but wants to retain the options and expertise which his or her dental laboratory technician can provide. Digital impression units also have a fairly short learning curve and require no changes to office protocols/job responsibilities.
CURRENTLY AVAILABLE IN-OFFICE CAD/CAM SYSTEMS
- CEREC AC Bluecam
Complete in-office CAD/CAM systems give the clinician complete control over the restorative process and the highly efficient potential to prep, fabricate, and restore in one appointment. The in-office CAD/CAM systems are made up of 2 components: the chairside digital impression unit, and the CAD/CAM chamber. The digital impression unit is placed chairside in the operatory and the milling chamber is placed in the dental office laboratory area.
The preoperative area is scanned, then, once the tooth preparation has been completed, the dentist or assistant will scan the area with the intraoral wand and capture the appropriate series of images (3 to 9 images for a single restoration) of the prepared arch, the opposing arch, and, as needed, the occlusion (bite). This process generally takes about one to 3 minutes to complete, depending on the user skill and case size and complexity. After the images are taken, the unit will compile the data and create a 3-dimensional model (no longer a "cast"). On this digital model, the user will check the bite alignment and scan to ensure accuracy, and then mark the margin with a digital marking tool. The software in the unit will now render a proposal for the restoration (Figure 12). The user then checks the contours, contacts, thickness, and anatomy of the prepared restoration design. Both systems offer a wide variety of tools to reshape the proposed tooth form. A great benefit to this digital technology is the ability of the dentist to create the contacts and contours to their exact demands. Once completed, the restoration proposal is sent to the CAD/CAM milling chamber. The appropriate block is inserted into the chamber, and the mill is started. About 5 to 15 minutes later, the restoration is nearly complete (Figure 13). The sprue is removed from the restoration, the restoration is tried-in, and the contacts and margins are checked. Appropriate adjustments are made, and the restoration is ready for finishing via polishing, staining, crystallization (as needed) and/or glazing.
|Figure 9. The Lava C.O.S. models are "printed" using a stereolithography apparatus.||Figure 10. The definitive PFM fixed partial denture is fabricated using traditional laboratory techniques.|
|Figure 11. The FPD is cemented to place, and requires no occlusal or interproximal adjustments.||Figure 12. The CAD/CAM systems (CEREC and E4D [shown here]) allow the dentist to check and modify restoration thickness and contacts before the fabrication process has even started. The color-coding on the onlay represents the varying thickness of the final restoration.|
|Figure 13. The CAD/CAM milling chamber (CEREC MCXL), following the creation of the onlay restoration. After removal from the mill, the restoration will need to be de-sprued, stained, and glazed.|
The in-office CAD/CAM systems offer the amazing and distinct advantage of giving full control of the restorative process to the dentist. Patients obviously love the possibility of having their porcelain restorations done in one visit. Dentists greatly appreciate the speed and control of these systems, in addition to the significant reduction in lab bills. As a result, there is a great potential for a high return on investment with in-office CAD/CAM systems.
The in-office CAD/CAM system is well suited to quadrant dentistry; they are, however, also capable of creating veneers and bridges. For more aesthetic and complex cases, where the expertise of a trained lab technician is needed, the scan data can be exported to a laboratory (via CEREC AC Connect or E4D Sky) to have more complicated or sophisticated restorations fabricated. These systems are also now able to accept cone beam computed tomography data and integrate this information with the intraoral scans for exceptional control over the implant treatment planning process (via E4D Compass and CEREC 3D planning).
DIGITAL IMPRESSION UNITS VERSUS COMPLETE IN-OFFICE CAD/CAM SYSTEMS
Clinicians looking to purchase a digital system are often confronted with a great deal of confusion in deciding which system would be right for them and their practice. The first important decision to make is whether they want a stand-alone digital impression unit or a complete CAD/CAM system. There is not one right answer for every practice, and all the units on the market today have strong track records.
There are several things to consider when investing in a digital impression system. Perhaps the biggest question to answer is whether or not you want to minimize the work done by the laboratory technician. Digital impression units (ie, iTero, Lava C.O.S.) still allow the dentist to take advantage of the technical expertise and experience of the lab technician; in-office CAD/CAM systems (ie, CEREC, E4D) do not. However, the in-office CAD/CAM systems (ie, E4D and CEREC) have the potential for a high return on investment due to the reduction of interaction with the laboratory.
It is also important to consider material selection. The stand-alone digital impression units allow the clinician to use any currently available material, from gold and PFMs to zirconia (ie, Lava) to feldspathic (ie, Vita VM 13 [Vident]). In-office CAD/CAM systems are primarily designed for use with different millable porcelains (ie, Vitabloc Mark II [Vident]; or IPS e.max CAD and IPS Empress CAD [Ivoclar Vivadent]), composite materials (ie, Paradigm MZ100 [3M ESPE]), or the latest resin nanoceramic (ie, Lava Ultimate [3M ESPE]).
Digital impression and CAD/CAM systems have already completely revolutionized the dental laboratory industry. It is only now, after being on the market for more than 25 years that the clinical digital impression units and CAD/CAM systems have really begun to take off in popularity. The technology gets more accurate, more efficient, and more intuitive with each upgrade, and now clinicians of all types have begun to see the distinct advantages these technologies have to offer.
In the coming months and years, there will be a flood of new improvements and newly introduced devices. In 2012 alone, 3 more devices are scheduled for release in the United States: Trios (3Shape), IOS Fastscan (Fastscan Technologies), and Directscan (Hint Els).
The increased competition in the digital impression and CAD/CAM fields will result in rapid innovation. These technologies have already begun to dramatically change what dentists and patients expect. The biggest paradigm shift in dentistry since the introduction of dentin bonding agents is well underway, and the development and subsequent applications of these technologies will undoubtedly revolutionize the practice of restorative dentistry.
Disclosure: Dr. Schoenbaum has previously lectured for 3M ESPE and Henry Schein.
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