Digital Impressions = More Predictable Dentistry

Digital Impressions = More Predictable Dentistry

Have you ever wished there was a better way to take impressions? How about a method that does not involve messy impression materials or pouring up and trimming models? Imagine being able to get an impression more accurate than the conventional impression techniques are capable of achieving.

The scanning technology of Cadent's iTero system digitally captures impressions that can then be used by your dental laboratory to make the indirect restorations of your choice. The iTero is designed to replace conventional impression taking methods which are often uncomfortable and imprecise. Currently, the most common applications include taking digital impressions for crowns, bridges, veneers, inlays and onlays. This system provides the precision, accuracy, fit, reproducibility and other benefits of the CAD/CAM world without the milling system and associated supplies and maintenance in-house. The inherent shortcomings such as the voids, pulls, distortions and the general margin of error in conventional impression techniques and modeling process are all eliminated.

Let's explore its use and clinical applications, and provide an overview of the benefits of the system in a clinical setting, possibly your dental office.

Clinical case

Mike, a 52-year-old male came to our office presenting with a large alloy restoration in tooth 29. He noticed that a piece of tooth structure broke off and it was sharp to his tongue. He knew it was time for another full coverage restoration since he had been down this path several times before (Fig. 1). Upon examining the tooth there were also 2 fracture lines and interproximal caries on the mesial of the tooth so we concurred with his request and the treatment plan agreed on was for a full coverage Lava crown.

 

Fig. 1

He chose our practice after seeing information on our website about our ability to take digital impressions. He stated that he was a strong gagger and was glad to learn there was a better way. We had used the iTero digital scanner in our office for almost 2 years and were confident it would work well for this patient as well.

Prep

The broken area was temporarily built up with composite resin and a Temp Tab was used to capture an impression to construct the temporary. The shade was taken with the Vita Easyshade Compact. This patients' shade was A-3.

After the patient was anesthetized with 1.6cc of 4% articaine with 1:200,000 epinephrine, the old alloy and decay were removed, the tooth was built up with Ketac Silver, and the preparation completed with a chamfer finish line circumferentially.

As with any impression technique, excellent retraction is a must. The method used in this case was to first pack Ultradent Ultrapak #2 cord for 5 minutes, followed by Expasyl for 5 minutes (Fig. 2).

 

Fig. 2

While the tissue retraction is occurring, the chairside assistant acquires the scans of the opposing arch - this takes only a minute or two.

Scanning

When the Expasyl was thoroughly rinsed, the first scans taken were of the prepped tooth. It is important on this first scan of the prep to be sure the margin is clearly visible circumferentially. If it is not clear, this is the time to reprep, repack, or both (Fig. 3).

 

Fig. 3

When I am happy with the images of the prep, the remaining scans of that arch are captured, taking only a couple of minutes. The last two scans are taken for bite registration (Fig. 4).

 

Fig. 4

The system guides you through the complete scanning process, showing and telling the tooth number and the angle for each scan. The total scanning time, both upper and lower segments normally is less than 4 minutes - often shorter than waiting for an impression to set. At this point the iTero stitches together the images and gives a preview of the prep and the model, including a color-coded occlusal clearance view (Fig. 5).

 

Fig. 5

This process is also very fast, no more than one minute. If any areas were missed by the first set of scans, additional scans can be taken of any area and they are then incorporated into the virtual model. I cannot emphasize enough the benefits of this immediate feedback on both the preparation and the model/digital impression. It is much better to find a problem now rather than have the lab have to call you later and tell you there is one.

The prepared tooth can now be viewed from all angles, both as a virtual stone model, and from the underside, as an impression, to make sure the margin is clear, that the prep will draw, and the axial and occlusal reduction is adequate. Again, if things are not exactly as you want them to be, they can be corrected while the patient is still anesthetized and still in the chair.

With the traditional impression technique I would only find out there was a problem was when the lab called and told me there was a problem with the conventional impression I sent in or the model they poured up, that the margin was unclear, it did not draw, or there was not enough occlusal or axial reduction. When this happens it becomes a very costly and time consuming situation. What is even more costly is if there were unnoticed distortions and the returned restoration fits the die, but not the tooth. Repeating the process is very costly, both for the lab and the dentist. It also can cause a strained relationship between the lab and the dentist, each blaming the other for poor quality or workmanship. Now these concerns are a thing of the past.

I also found two unexpected benefits of this system. The first unexpected benefit of seeing your preparations on a large screen from every angle possible is to suddenly have much more empathy for your lab technicians and the challenges they face. The second is that your preparation and retraction methods improve dramatically.

Of greater value is the patient experience up to this point. Mike was very pleased with the scanning process and thankful he did not have to go through the traditional method and gagging process. He was also very impressed with how quickly the virtual model appeared on the screen and that he could see what we had actually done. This process also cements the perception that the office is state-of-the-art and that they are receiving the best care available. Since the experience of actually seeing their virtual model is so unique, I am sure he will talk about it with his friends and family, which is an unexpected but effective practice builder.

When I was happy with the virtual model and prep, a temporary was constructed using 3M ESPE Protemp Plus and cemented with GC TEMP Advantage. Post op instructions were given, the seating appointment was set for two weeks out and the patient was dismissed.

The completed scans are then sent to the lab via the internet at the click of a mouse. No getting lost in the mail, no transportation costs, and best of all, no infection control concerns.

Seating

The most rewarding part of the process is the seating appointment. The crown comes back on a milled polyurethane die and model that is very abrasion resistant. The die is accurate to within about 20 microns. It is very stable and the die is not able to move so the contacts are always right on. The models are held in a specialized articulator that relates the opposing jaws very accurately (Fig. 6).

 

Fig. 6

In this case, the total time the patient was in the chair to seat the crown was under 10 minutes, which is now the norm in my office.The temporary was removed, the restoration was tried on with Kerr Nexus try in paste, the patient bit together and said "Wow, it feels great - usually it takes a lot of adjusting to make the crowns fit."The contacts were checked with floss and they were fine, the occlusion was checked with articulating paper and it marked perfectly. A quality control radiograph was taken was taken (final x-ray) and the margins were right on. The esthetics were checked and both the patient and myself were very pleased with the result (Figs. 7 and 8)

 

Fig.7

 

Fig. 8

The crown was removed and cleaned, as was the tooth and then the crown was cemented with GC FujiCem. After the two minute set time, the excess cement was removed, post op instructions were given and the happy patient was able to continue his day.

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