The Cutting Edge of Scanning and Milling

Justin McElroy, Vice President of Business Development for Midwest Dental Arts in Sarasota, Florida, utilizes some of the most advanced technology for milling full-arch restorations on a daily basis. Inside Dental Technology spoke with McElroy about what he is doing, how he is doing it, and why.

Inside Dental Technology (IDT): What kinds of things do today's scanning and milling technologies make possible?

Justin McElroy: A significant amount of my focus has been on zirconia—milling veneers or full-mouth rehabilitations—because the strength and esthetics are so impressive. Milling is so much more predictable than a pressed workflow. We are also utilizing photogrammetry for full-arch cases, which has increased the accuracy of our screw-retained restorations; with that technology, we are milling 95% of our full-arch cases directly to the multi-unit platform without Ti bases.

IDT: What makes that so impactful?

McElroy: Many laboratories cannot predictably mill a screw channel that is slightly tapered with a direct connection. Often, the screw will not even fit through the zirconia prosthesis. Patients frequently break their temporary restorations, and that is often because of the inaccuracy of not only traditional impressions but even many digital impressions. The temporaries are just not fitting 100% passively, which leads to stress on the prosthesis and the screws. With photogrammetry, I can be certain that my milled prosthesis will screw in perfectly, and by eliminating the Ti base in the final screw-retained prosthesis, I can avoid debonding issues and subsequently strengthen the prosthesis.

IDT: How exactly does photogrammetry work?

McElroy: We place scan bodies on the multi-unit abutments, and utilize an extraoral scanner with four cameras on it to obtain the true position of those implants. With an intraoral scanner, the cross-arch accuracy is undetermined; a variety of issues will always require the traditional verification process to ensure that the final prosthesis fits. With photogrammetry, we can actually see the alignment in real time while the patient is sitting in the chair. This makes the entire process more efficient and also leads to a better final outcome.

IDT: When you mill these restorations, are there specific CAM software or hardware requirements?

McElroy: A five-axis mill is important. We have had engineers from the software companies visit our laboratory to work on the milling strategies for these particular cases. That has really been key because when we first started doing this, it was really frustrating at times. A bur would break and we did not know why. Zirconia would have microfractures after sintering. So much precision is involved that it is understandable for many laboratories to prefer the traditional utilization of Ti bases on every case. However, with so many cases, finishing and firing becomes significantly easier when a Ti base does not need to be bonded in, creating another level of inaccuracy.

IDT: How difficult is this workflow to implement?

McElroy: It is a challenge, but I believe it is necessary in order for laboratories to be competitive in the full-arch market. Those who wait until 2 years from now probably will be too late. The biggest change, however, will be in-office; I believe many "super GPs" and oral surgeons will create in-house laboratories and workflows to enable them to 3D print same-day temporaries, so that the traditional laboratory only needs to mill the final prosthesis. The full-arch market is so competitive because patients are aware of what can be done, and they are finding the providers who can do it.