Decoding CAD/CAM and Digital Impression Units

OVERVIEW
The indirect restorative procedure workflow is currently undergoing a significant change. Every few decades, the impression protocols have undergone a significant shift: from copper-bands and compound, to rubber base, to reversible hydrocolloid, to vinyl polysiloxane (VPS), and now to digital capture. Each system worked sufficiently well for its time; however, the demands for accuracy, efficiency, and patient comfort produced a strong impetus for change. In all prior cases, this change was evolutionary, but the shift from physical impressions to digital impressions may well prove to be revolutionary.
Although the technological means of creating an intraoral digital impression of the prepared teeth has been in the marketplace for more than 20 years, it is only recently that it has reached the levels of accuracy and efficiency that our profession demands. In just the last few years, dentistry has gone from a single intraoral digital capture device to 4 (Figures 1 and 2). There are 2 general types of these digital capture devices. There are those capable of a digital capture and in-office milling of the prosthesis (CEREC AC Bluecam [Sirona] and E4D Dentist [D4D Technologies]); these are commonly referred to as chairside CAD/CAM units. There are also those that take digital impressions but retain the fabrication procedures in the laboratory (LAVA C.O.S. [3M ESPE] and iTero [Cadent]); these are commonly referred to as digital impression units (DIUs). For those who do not wish to fabricate restorations within the dental office setting, the CEREC and E4D systems now also allow the choice of taking the digital impressions in the office and transmitting the data for the design (CAD) and milling process (CAM) in the laboratory (CEREC Connect [Sirona] and E4D LabWorks [D4D Technologies]).

Figure 1. Capture Units - from left to right: LAVA C.O.S. (3M ESPE), iTero (Cadent), E4D Dentist (D4D Technologies), CEREC AC Bluecam (Sirona).

Figure 2. Wands - from left to right: LAVA C.O.S., iTero, E4D Dentist, CEREC AC Bluecam.

Figure 3. Preoperative image.

Figure 4. Preparation image.

Figure 5. LAVA C.O.S. screen-capture of preparation following quadrant scan of prepped arch.

Figure 6. LAVA C.O.S. sterolithography resin model of prepped quadrant illustrating the trimmed and ditched die ready for restoration fabrication.

Figure 7. Bonded pressed ceramic (high-leucite reinforced) onlay.

Figure 8. An example of iTero’s CAD/CAM milled (resin) Geller-type model.

Figure 9. One of the CEREC milling chambers with a ceramic block in place and ready to be milled.

Figure 10. The E4D milling chamber with a ceramic block in place and ready to be milled.

DIGITAL IMPRESSION UNITS (DIGITAL IMPRESSION CAPTURE, LABORATORY FABRICATED RESTORATIONS)
DIUs capture the operative environment by taking a video, or, a succession of images of the teeth. This data is compiled by the computer to create a 3-dimensional (3-D) digital model that is then uploaded to a digital center that optimizes/fixes/correlates the images and then to a proprietary model manufacturing facility. The manufacturing center creates the models via a CAD/CAM milling process (iTero) or a resin printing process known as stereolithography (LAVA C.O.S.). In some cases, zirconia copings can also be made directly from this data as well (LAVA C.O.S.). The resin models are shipped to a dental laboratory of the doctor’s choice to have the restoration fabricated. In most cases, the mounted models arrive at the laboratory 2 to 5 business days after the preparation appointment. Both the LAVA C.O.S. and the iTero systems allow the fabrication of restorations in almost any dental material.
The DIUs represent the fastest and easiest way to bring the digital workflow into the practice. They do not require any significant change to the day-to-day systems and operations of the practice. They do not require any significant change in the material inventory of the practice. They do not require the doctor or any member of the team to be trained in ceramic procedures. However, they do still require impeccable soft-tissue and moisture control, as well as smooth and refined preparations.
Both the iTero and LAVA C.O.S. DIUs come with in-office training (the amount/length of training varies, depending on the manufacturer) to get the dentist and team comfortable in using their system. This will help the team understand the scanning procedure, navigating the interface, and managing the digital workflow. Following this training, the digital impression procedure merely replaces the traditional techniques that were previously used. Total scan times are slightly faster than standard VPS setting times. In addition, recent legislative changes in some states allow registered dental assistants to take digital impressions. This reduces or eliminates the amount of time required by the doctor to obtain a final impression. Most dental laboratories will require the same amount of time to fabricate restorations from the digital models as they do for traditional VPS models.
By simply moving the entirety of the model processing workflow from the dental laboratory into the digital realm, the step-wise introduction of errors is significantly decreased. These units do not create the restorations in-office.

Advantages:

     1.Ease of integration
     2.Positive patient perceptions
     3.No inventory
     4.Shorter learning curve
     5.Allows the fabrication of any type of restoration
     6.Ability to integrate with future digital developments.

Disadvantages:

     1.“One-day dentistry” is not possible
     2.Upfront investment
     3.Does not reduce lab bill
     4.Per use fee, and per model fabrication fee.

There are 2 DIUs currently on the market: the LAVA Chairside Oral Scanner, or C.O.S., and the iTero. Both units are comparably priced.

LAVA C.O.S.
Workflow. The LAVA C.O.S. uses a handheld wand to record a digital video (using LEDs as the light source) of the prepared (and powdered) arch (or quadrant), opposing arch, and the buccal surfaces in centric occlusion. During the scan, the operator watches the touch-screen monitor (not the wand) for real time feedback of what areas have sufficient data. Areas that have sufficient data show up as a white color, areas with almost enough data are pink, and areas that do not yet have any data are blackish. This assists the doctor during the scan to see what areas need more data without having to stop and restart.
Upon completion of the scan, a 3-D digital model is rendered on the screen for the operator to review. Part of this review process involves checking the prepared teeth to ensure that all margins and relevant surfaces have been captured (the equivalent of checking an impression). This review is done on high definition 3-D images using 3-D glasses. Following the review, a digital prescription is completed and the data is sent off wirelessly to the laboratory.
After the data leaves the dental office it goes to a digital technician where the margins are marked, the dies ditched, models occluded, and mounting verified. This process is performed in a complete digital environment using the very same 3-D images the doctor just reviewed. If the doctor prescribed a LAVA zirconia crown, the data is simultaneously sent to an authorized LAVA milling center to have the LAVA coping designed and milled directly from the digital data.
The data is then sent to the model manufacturing facility where a stereolithography apparatus (SLA) “prints” each component of the model from a specialized resin. After being verified for accuracy, the models are shipped to any lab previously determined by the doctor where the restoration is now fabricated. A case example with the LAVA C.O.S. can be seen in Figures 3 to 7.

     1.User interface. The LAVA C.O.S. uses a touch screen interface. An on-screen keyboard appears for entering patient information and filling out prescriptions. The intraoral wand also has a start/stop button. There is no keyboard, mouse or foot pedal.
     2.What it does. The LAVA C.O.S. captures the 3-D surfaces of the teeth directly in the mouth using video capture. This data is then used to create SLA resin models from which any restoration can be fabricated.
     3.Unique features:
           a. Real-time Video Capture and feedback (3-D-in-motion)
           b. Intuitive touch screen interface
           c. LAVA (Zirconia) copings can be milled in the
               laboratory direct from the capture data.

iTero
Workflow. The iTero system utilizes parallel confocal imaging (laser), capturing a series of 21 images with a handheld wand to create a digital impression of a quadrant. The teeth require no powder. Each image of the preparation needs to be verified by the user before moving on. This is done utilizing the wireless foot pedal. To make the capture of 21 images easier, the iTero actually speaks to the user, indicating which surface and which tooth needs to be captured next.
Upon completion of the image series, the model is ready to be reviewed. A 3-D model is rendered, which the user can review, check clearances, and manipulate with the wireless mouse. After verification of the digital model and prep, the data is wirelessly uploaded to the iTero model milling center. The iTero models are milled from resin blocks using a CAD/CAM system. They are done in a Geller style, which preserves the soft-tissue profiles on the model. These models are then shipped to the laboratory, where they are mounted on iTero’s proprietary hinge articulator, and the restoration fabricated.

     1.User interface. The iTero utilizes a wireless foot pedal during the image capture process to allow the operator to confirm or retake each image. The pre- and post-capture input is done with a wireless mouse and a sealed keyboard.
     2.What it does. The iTero captures the 3-D surfaces of the teeth directly in the mouth using a confocal (laser and optical) image series (usually about 21 images). This data is then used to create CAD/CAM resin models (Figure 8) from which any restoration can be fabricated.
     3.Unique features:
           a. True powder-less image capture
           b. Talks user through each of the 21 images
           c. Geller-type models.

DENTAL CAD/CAM UNITS (DIGITAL CAPTURE, IN-OFFICE RESTORATION DESIGN AND MILLING)
Dental CAD/CAM units consist of 2 primary components: the digital capture/design unit and the milling unit. Dental chairside CAD/CAM units allow the start-to-finish design and fabrication of a restoration completely within the dental office. Recent developments also allow the user the freedom to export the digital model to a laboratory for restoration design and fabrication, as well as model fabrication. The digital capture unit allows the clinician to capture a series of images that will create a 3-D digital model. On this digital model, the restoration will be designed by either the doctor, a highly trained auxiliary, or exported to a laboratory.
The in-office process requires that the user digitally mark the margins and make any necessary changes to the anatomic form proposed by the computer. Occlusion and interproximal contacts must also be checked and adjusted as necessary. Following the design stage, the proposed restoration is sent to the in-office milling unit. The milling unit must be loaded with the appropriate ceramic (or composite) block, as determined by the type of material to be used, the size of the restoration and the shade. The milling times vary by unit size, detail, material and milling unit, but are generally in the range of 6 to 15 minutes per unit.
After the restoration has been milled, it must be checked for fit and then finished. It is generally advisable to check the fit and occlusion prior to finishing in order to expedite the process. (Depending upon the type of all-ceramic being utilized, one must exercise caution when adjusting occlusion prior to cementation/bonding. Check with the manufacturer or your dental laboratory technician.) Finishing can be accomplished by polishing, by staining and glazing, or by cutting back and hand stacking porcelain. Simply polishing the restoration is the most efficient method, while the cut-back and stack method is the most aesthetic. As an alternative, there are now polychromatically blended ceramic blocks available that can produce a more lifelike result (ie, VITA CAD-Temp multicolor blocks [Vident]; IPS Empress Multiblock [Ivoclar Vivadent]). Following finishing, the restoration is ready for etching and silanating.
The Dental CAD/CAM units allow the dentist to have full control over their restorations from start to finish. With sufficient dedication, these units can radically alter a practice and allow “one-day” dentistry with a reduced overhead.
Though signifcantly more involved than the DIUs (LAVA C.O.S. and iTero), the In-Office CAD/CAM units (CEREC and E4D) can provide a more complete digital experience for the doctor and office looking to completely transform the way they currently operate. Basic training and guidance is provided with the newly purchased unit to allow the user to complete acceptable results under average conditions. More sophisticated and advanced training is generally required for multiple units and aesthetically demanding cases. Training in stacking, staining, and glazing of porcelain is also recommended for any office looking to create restorations at a high aesthetic level. The recent introduction of the ability to export the data to a lab (CEREC Connect; E4D Labworks) will prove to significantly expand the options and integration protocols in practices looking to get started in digital dentistry while retaining the option to add an in-office milling unit in the future.

Advantages:

     1.Complete control over the indirect restoration procedure
     2.“One-day” dentistry possible
     3.Ability to significantly reduce lab bills
     4.Positive Patient perception
     5.Option to export data to the laboratory for fabrication.

Disadvantages:

     1.Significant upfront investment
     2.Requires an inventory of blocks and sizes
     3.Significant training and auxiliary support needed
     4.Depending on the skill/training of the dentist/team
      (ie, ability to stain/glaze in-office, or presence of an in-house ceramist)
      aesthetics of in-office restorations may not be equivalent to those created by skilled ceramists.

There are 2 dental chairside CAD/CAM units currently on the market: the CEREC AC Bluecam, and the E4D Dentist.

CEREC AC Bluecam
Workflow. The CEREC AC, powered by Bluecam, is Sirona’s latest in-office CAD/CAM device (CEREC was originally introduced to the market in 1987). It can be paired with either of 2 milling units (Figure 9). The intraoral digital impression is taken as a series of top-down images of the prepared teeth which have been properly powdered. The Bluecam is exceptionally fast and captures an image each time the wand is positioned over the teeth. This is convenient as it removes the necessity of a pedal or button.
Following capture of the preparation arch, a bite registration is taken, and the teeth are powdered and scanned. This then allows the computer to properly create the occlusal contacts. The user must mark the margins and then modify the proposed restoration as needed for the desired contact strength, location and shape, as well as the overall anatomy and position. Generally, the proposed restoration requires only minimal modifications. The unit can also be set in the correlation mode to recreate the preoperative condition.
The appropriate block (size, shade, and material) is then loaded into the milling chamber. Upon completion of the milling cycle, the sprue is removed and the restoration can be checked for fit and contact before finishing. The restoration is then finished by polishing, glazing or stacking.
CEREC has the benefit of being able to send the digital impression to authorized labs through a program called CEREC Connect. From the digital data, the lab can design, mill and finish the restoration. This can be a convenient and flexible option for offices that have no desire or time to perform the ceramic work in office.

     1.User Interface. The CEREC AC utilizes a sealed keyboard and a trackball for data input and manipulations. The intraoral capture wand offers foot pedal use; however, automatic capture is most often used.
     2.What it does. The CEREC AC can produce almost any indirect restoration (inlays, onlays, crowns, veneers, etc) from a variety of materials (composite, sintered feldspathic, high-lucite reinforced, and lithium disilicate porcelains.) When the data is sent to a lab with an in-lab milling unit, zirconia-based restorations can also be produced.
     3.Unique features:
          a. Fastest capture (with Bluecam)
          b. Flexible purchase options (pay-as-you-go)
          c. CEREC Connect allows lab-fabricated restorations.

E4D Dentist
Workflow. The workflow for the E4D Dentist is very similar to that of the CEREC with a few, but significant differences. The E4D Dentist captures images using a laser, obtained from 3 separate angles (buccal, lingual, and occlusal) for each tooth. This helps to reduce any error that might be introduced by automated “patching” (filling in) of areas that are below the height of contour and cannot be picked up from a top-down image alone. However, it does increase the number of images that must be taken.
The E4D Dentist can also perform the image capture without the use of a contrasting powder. The E4D Dentist also has the added benefit of being able to manipulate multiple restorations (up to 16 at once) within the same window.

     1.User interface. The E4D Dentist utilizes the familiar wireless mouse and keyboard setup for data input and manipulation. The camera wand is operated by means of a remote foot pedal, or automatic scanning (Rapid Scan [D4D Technologies]).
     2.What it does. The E4D mill (Figure 10) can produce all types of indirect restorations (inlays, onlays, crowns, veneers, etc) from a variety of materials (composite, leucite-reinforced and lithium disilicate ceramics.) The recently introduced E4D Labworks and E4D Sky (D4D Technologies) communication will allow dentists to export the digital models to the laboratory for design and fabrication, and also allow for virtual communication. This will increase the integration options for the dental practice that may not have the time, skill or desire to fabricate final restorations in-office.
     3.Unique features:
          a. Powder-free image capture
          b. Multiple-angle image capture
          c. Multiple restorations can be designed in a single window (up to 16)
          d. Remote access and support (S.O.S.) systems are “on-line”
          e. Free software upgrade and updates.

DECIDING FACTORS (DIUS VERSUS CAD/CAM UNITS)
In dentistry, like everyday life, new technologies are radically changing the way we see and do things. Many of the processes and materials we have already incorporated into the scope of everyday practice are possible only with these new developments. Digital cone-beam computed tomography (CBCT) scans have become irreplaceable for the evaluation of implant and grafting sites. Digital intraoral x-rays have enhanced the speed and diagnostic abilities of the clinician. Zirconia (ie, LAVA) utilizes a lab-based CAD/ CAM unit for fabrication. Digital photography has revolutionized our ability to communicate with patients, technicians and colleagues. The “paperless practice” is becoming more and more common in dentistry, as well as in medicine. Insurance claims can be submitted digitally. To stay competitive in today’s market, the dental lab business is also moving quickly to various modalities of digital technology (ie, wax printing, stereolithography, CAD/CAM milling.)
No one digital technology is right for every practice. Clinicians must carefully evaluate and consider their goals when looking to adopt digital impressions and/or In-Office CAD/ CAM into their practices.
The DIUs (LAVA C.O.S. and iTero) are best suited for the practices that already function at a very high level (or are hoping to). These are the practices that enjoy the convenience (in terms of fit, design, and aesthetics) of a restoration produced by a third party (dental laboratory), but are also interested in realizing all the benefits that digital impressions have to offer. DIUs are best for doctors who have no inclination to design and finish their own ceramic (laboratory) work.
DIUs do require some brief training to get through the learning curve. However, once the team is comfortable with the scanning procedure, this technology fits very easily within an efficient office protocol. There are almost no changes to inventory or scheduling required. Patients generally prefer the digital impressions to physical (ie, VPS) impressions, which can significantly increase goodwill and word of mouth referrals.
The in-office chairside CAD/CAM systems (CEREC and E4D Dentist) are best suited for the office that wants to enhance efficiency and reduce overhead, while bringing the entirety of the ceramic workflow into the office. Integrating these units into a practice requires a strong drive to make it work and the support of a competent team. Once fully integrated, the reduction in lab bills can be quite significant and result in a significant decrease in overhead. The prospect of “one-day dentistry” and the “wow factor” of the technology may also help to attract new patients.

Table. Digital Dental Units Comparision Chart
 
Digital Impression Units
In-Office CAD/CAM Units
  LAVA C.O.S iTero CEREC AC Bluecam E4D Dentist
Ditgital Impressioning X X X X
In-Office Milling     X X
Export to Lab X X X X
Zirconia X X X (in-lab)  
Interface Touchscreen Mouse, Keyboard,
Foot pedal
Trackball,
Keyboard,
Foot pedal,
Automatic capture