Complementary Digital Technologies

Since the early days of dentistry, practitioners have strived to reproduce the intraoral dental condition outside of the mouth. Until recently, the only available means to accomplish this was by taking an intraoral impression, which enabled the dentist or technician to make a stone model of the teeth, gingiva and/or the edentulous areas.

Darwinian impressioning

The accuracy of these impressions has improved as materials have developed over the years - from impression plaster, compound in copper bands, reversible hydrocolloid, polysulfide rubber base and polyether - to today’s standard of vinyl polysiloxane. However, even with the current generation of materials, challenges remain in obtaining an accurate impression and model.
Dimensional changes in the impression materials and the stone models can distort the reproduction of the important areas. Issues such as moisture sensitivity, blood contamination, tearing of the sensitive thinner areas of the impressions (especially the sensitive margins of the preparation), and bubbles and voids in the materials can make the effort to accurately reproduce the desired areas very taxing.
Distortions in the models are not always visible and we may get a restoration back from a hard working laboratory technician that fits the model, but not the mouth. If the restoration does seat intra-orally, it may require significant adjustments to get the proper occlusal or interproximal fit.
In an effort to combat this problem, Siemens came out with CEREC One in the late 1980s which contained a three-dimensional camera to image tooth preparations and create a virtual model. For nearly twenty years, it was the only digital impression method commercially available and the CEREC software has steadily improved, giving the clinician or technician the ability to more easily create different types of restoration designs in one visit. However, the imaging system has not changed and continues to require an optical powder medium to properly image the desired area.
Several other companies have since introduced digital impression taking devices. E4D is directly competing with CEREC 3D in the one-visit restoration market and creates a digital impression without the use of powder in most cases.
3M has introduced its Lava Chairside Oral Scanner, which is a camera that takes a real time video digital impression of the teeth, although a slight amount of powdering is required. The image is then sent to 3M, whereupon a model is created.
In May 2006, Cadent Inc. introduced the iTero digital impression system. Since then, more than 60,000 restorations have been created from the CAD/CAM models precision milled from the digital scans. The iTero system uses a technology called parallel confocal imaging which is different than the triangulation sampling method used by the 3M and CEREC cameras. No powder or additional contrast medium is required of the iTero scanner. In fact, the wand may touch the surface of the teeth during the scanning process without contaminating the image.
Prior to getting the iTero system, I used the Cerec process for almost every single unit restoration that I made. However, I still took VPS impressions for multiple unit restorations, and multiple unit cases. As a satisfied CEREC user, the integration of the iTero scanner into my practice was seamless. Following is a typical case.

Case Study

At her regular recare appointment, the examination of a long time patient of mine showed a failing composite resin restoration in tooth # 30. Recurrent decay has undermined the DB cusp. Since she had a poor margin on # 31, and fractured porcelain on the occlusal surface of this crown we decided to replace both restorations (Figs. 3, 4, 5).

Since Kim is a bruxer, and the previous porcelain fused to metal crown failed, I decided that I wanted to restore her with the most durable materials. Kim did not want gold, and we decided to make a porcelain onlay on # 30, and porcelain fused to zirconia core on # 31. This work would have to be sent to a laboratory.
After anesthesia, tooth preparation retraction cord (Gingi-Plain Z-Twist) was placed. I use a black cord which provides a nice contrast between the tooth and the tissue. It enables me to see my margins and the displacement of the gingiva (Fig. 6).
I next began to scan the prepared arch (Fig. 7) (I had chosen the option to scan the opposite arch first. This was done while waiting for the onset of anesthesia). The system directs you through the process with a series of voice prompts and illustrations to indicate the view of the teeth that it requires. The first scan is always of an entire preparation. You are shown a preview of the scan to ensure that all margins are visible. If so and you are happy, you then move on to other views of the preparation, and the adjacent teeth. The final scans are of the arches in occlusion.

Provisionals were made, and the patient was appointed to return for the placement of the final restorations.
One of the nice features of the ITero scanner is that you can rest the scanner directly on the teeth. This aids in stabilization. In addition, the unit will only scan when there is no movement. You can activate the scanner, obtain your best view and the scanner will fire automatically when the field is stable.
After completion of all of the scans the computer constructs a lower resolution model of the arches and the occlusion. The model also tells you how much occlusal reduction exists via a color map. If you are not happy with that, you can adjust your preparations and rescan (Figs. 8, 9, 10).
One of the difficulties of doing multiple restorations with the Cerec 3D system is getting all of your images to knit together. Variations in the roll, pitch, and yaw of the camera, as well as the position of the image in the frame may make it impossible for the computer to put all of the images together. Much of the time that I spent learning to use the Cerec 3D system was spent on being able to take proper images so that the system could combine them. That is not a problem with ITero. Because of the great amount of data that the laser obtains, the images are combined effortlessly. In addition, the ITero scanner projects a “viewfinder” onto the image facilitating the job of the operator in obtaining the correct image.

Upon completion of your scanning, you click a button on the program, and your file is wirelessly transmitted to ITero (Fig. 11).

They enhance the image, verify the margins with the laboratory and deliver a working model with trimmed, ditched removable dies directly to your lab (the position of the margins and the ditching is done virtually on the computer). The laboratory fabricates the restorations in their normal manner, and delivers them to you as agreed (Figs. 12, 13, 14).

After removing the provisionals and cleaning the preparations the restorations were tried in the mouth. Figs 15, 16, 17 are of the initial restoration try-in. I did no adjustments to get these restorations to go to place. It was effortless! I cemented them with Kerr’s MaxCem Elite and finished and polished the margins in a normal fashion. No occlusal adjustment was necessary.

Conclusion

The development of the infra-red camera for Cerec 1 was the first step in providing the dentist with a truly a digital dental experience. (Editor’s note: Since the writing of this article, the CEREC AC System has been introduced, which uses a Bluecam LED acquisition camera). The Cerec operator is able to manipulate the scanned images and create a restoration using the Cerec 3D software and a compatible milling unit.
Cadent’s ITero system is the next big advance in the art and science of dentistry. The precision of the optical scan enables the operator and laboratory technician to provide a most superior restoration. Removing many of the materials, and operator variables enables us to more predictably provide the quality of restoration for which we strive- and it makes it easier to do so! Sirona (CEREC) and Cadent (ITero Scanner) are working together to enable the dentist to use the superior ITero scanner and send the ITero digital impression to the lab whereby the lab can use the Cerec software to design and produce a coping or crown, and return it to the dentist. This is a good first step. I hope that soon these companies working together will enable the dentist to make a one-visit restoration in the office using the ITero Scanner with the Cerec 3D system.




The iTero Scanning System
With my CEREC background, I was already comfortable retracting the gingiva to enable the camera to clearly see the margins. The technique and materials are the same as with conventional VPS materials. I can either pack retraction cord and leave it in place with the preparation margins exposed, or I trough the gingiva with my diode laser . Regardless, I can see the accuracy of my scan in real-time on a video monitor. Even without the CEREC experience, I would have easily adapted to the iTero scanner – it has a short learning curve.
After imaging the preparation(s) and adjacent teeth (including the opposing arch and the teeth in occlusion); a process that takes about the same amount of time as a conventional impression, the file is wirelessly transmitted to Cadent in Tel Aviv, Israel, which processes the high resolution scans and verifies the margins with my lab. Future software updates should enable me to become part of this process. Once the margins are verified, the file is sent to a Cadent facility in New Jersey where an industrial 5-axis milling system is used to manufacture a model with removable dies out of a proprietary resin material. (figures 1 and 2). The model is then sent to my chosen lab for restoration fabrication.

The ITero models (Figs. 1,2) are milled from a proprietary polyurethane material that demonstrates the material characteristics of low wear, breakage resistance, chipping resistance, low moisture absorption, and no shrinkage. There is no shrinkage because the models are milled directly from the final hardened material. There is no pouring, or curing during this process, and therefore no dimensional changes that one would experience with dental stone. (See table one)

ITero users, including myself, are thrilled with the fit of the restorations. Contacts are spot on and most importantly, the occlusion needs little or no adjustment (which, in my opinion is the biggest benefit of using iTero). My seat time has been reduced dramatically and in some instances, my laboratory technician and I have chosen to forego a metal try-in on fixed partial dentures and have completed the restoration in two visits.
Laboratories may have to be re-educated about the precision of the iTero models. It is no longer necessary to overbuild contacts or occlusion to guarantee that the clinician can make the restoration fit at the time of that seat appointment. The technician can create the perfect restoration with assurances that it will find its way into the mouth virtually unchanged.

*Information provided by the manufacturer