View from the Chairside: Does digital scanning work on deep preparations?
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.
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.
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.
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.
Here is the proposed restoration in full occlusion.
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.
After a quick stain and glaze (approx 20 min), I cemented the final restoration with MultiLink.
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.
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.
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.
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