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View From The Chairside

View from the Chairside: Does digital scanning work on deep preparations?

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By Dr. Amarjit Rihal

Dr. Amarjit Rihal graduated in 1995 from the University of Manitoba and is a partner in a large group practice. Currently, he is the President of the Manitoba Dental Association and serves on the boards of the National Dental Examination Board (NDEB) and the Commission on Dental Accreditation of Canada (CDAC). Dr. Rihal’s interests include CAD/CAM and implant dentistry and he currently is a mentor for CERECDOCTORS.com

I get many questions about the accuracy of making digital impressions/milling equipment when dealing with the margination of deep restorations. With Cerec’s Omnicam you are not limited to supragingival preparations. My answer is, if you can isolate a prep to take a conventional impression, you can acquire a digital image. Here is a premolar that has a deep preparation in it post root-canal treatment. Our treatment plan was to do an Emax lithium discilicate crown on that tooth.

Picture 1

With any Emax preparation, you want to capitalize on any enamel you can find. As you can see in my preparation that was easy to achieve on the mesial aspect of the tooth, but the distal portion ended on the root surface of the tooth. Even if I am 4 mm subgingival on the distal, this can be faithfully captured by my Omnicam.

Picture 2

After scanning the preparation, the antagonist and the bite, you can see the degree of accuracy in the high resolution scan. One of the biggest advantages of the OmniCam is that it captures its data in colour. What does that mean? It means that you can discern the tooth structure, retraction cord, and gingival tissue with ease. After scanning, the next step in the digital work flow is to highlight where the margin is as shown in the next slide as a blue outline.

Picture 3

After telling the computer what parameters I would like (virtual die spacer, proximal contact strength etc…), the Cerec software looks at the anatomy of the adjacent teeth and formulates a proposal that matches the look, feel and contour of what is already there. It is not just a dentiform looking tooth. Cerec defines this concept as ‘Biogeneric’ design and it is truly unique. Look at the following proposal, the light blue dot signifies on occlusal contact, which is adjustable by me, if I so choose.

Picture 4

Here is the proposed restoration in full occlusion.

Picture 5

After I made my adjustments, I milled the restoration in about 10 minutes. I like to try in the partially cured ‘blue’ phase Emax. Notice how the occlusal contact matches my computer proposal, it is that accurate.

Picture 6

After a quick stain and glaze (approx 20 min), I cemented the final restoration with MultiLink.

Picture 7

Here are some pre- and post-xrays showing the beauty and accuracy of the fit of the Cerec milled Emax crown. As you can see, the initial amalgam restoration was deep and situated on the root surface of the tooth.

Picture 8

Our post-op xray shows the intimacy of the fit of the milled restoration. Also note that the proximal contour seems to flow naturally from the tooth to form a nice broad proximal contact. I control all these features in the software when I make my design.

Another characteristic of the lithium discilicate materials is their radiolucent appearance. This will facilitate your diagnostic capability, and when bonded to the tooth will have a compressive strength of over 1000 MPa. No lasers were used during my clinical procedure, just conventional retraction cord and a steady hand.

Picture 9

Oh did I mention that I did this all in about 1.25 hours! No second appointment, no impression material, no temporary crown. That is the power of digital dentistry.

If you have any questions about this or anything else about digital dentistry, please contact me at arihal1@me.com

 

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6 Comments

  1. Thomas Shackleton September 17, 2013

    Very nice case! Technology – what’s not to love? Thanks for posting this

    Tom

    Reply
  2. CLiff Leachman September 17, 2013

    Looks like a gap ,under the distal to me? Metal margin would have given more likelihood of long term success.

    Reply
    1. Amarjit Rihal September 18, 2013

      Hi Cliff, thanks for your comment. I think the pa I posted doesn’t show much of a radio-opaque cemental line. Clinically when I cemented the marginal fit was good (no gap) and was sealed with a non-resorable resin cement (multi-link) which I finish with a reciprocating polishing device. In CEREC you can invert the preparation and check your marginal/cemental gap and adjust it to be thinner and tighter as you see fit. The result a varying display of a cemental line. I often find the radiographic nature multilink can be variant. I’ll followup with the case and post a bitewing and photo when he is in on a recall. Thanks again….

  3. Dr. Jonathan Suzuki September 19, 2013

    That’s amazing! Any reason why you did the 2nd premolar first? The molar behind it could use a crown as well — its an amalgam tooth

    Reply
    1. Amarjit Rihal September 19, 2013

      Hi Jonathan, the #46 and #47 will be done in the new year together when his insurance rolls over again. I will do an emax on #46 and a FVC on #47. We can virtually design a CAD wax block for a FVC, try it in and then send it to a lab to get casted, we mill out a temp crown when we are trying in the CAD wax block. The cement usually needs no adjustments… Talk to you soon!!

  4. Dental Studies in Toronto January 13, 2015

    Digital dentistry offers various advantages in treatment. With the help of such technologies, dental treatments are getting much better. Thanks for sharing the pictures and way you cemented with the help of digital scanner.

    Reply

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