All Digital, Implant-Supported Hybrid Prostheses
August de Oliveira, DDS, on exocad digital workflow
Some people like a challenge. I, on the other hand, prefer a good no-brainer. Even after I had been placing and restoring implants for a while, the complex process of providing an implant-supported hybrid prosthesis using conventional protocols always seemed shrouded in voodoo. First, you have to make sure that your multi-unit abutments are lined up right. Then you take an impression, but it isn't for the final. It's just to create a custom tray and something called a verification jig. Next, you screw the sectioned jig to the implants, glue the jig back together in the mouth, and make sure that it is picked up in the final impression—all while dealing with the anxiety of burying the open tray impression screws in the impression itself. Finally, you have to figure out how to capture a bite registration for a patient who is fully edentulous. There are just so many steps in the conventional process.
Conversely, many believe that you can just whip out your trusty intraoral scanner and digitally provide a full mouth implant rehabilitation like you were performing an inlay on tooth No. 4, but it doesn't work that way. Intraoral scanners take hundreds of images and "stitch" them together into one model. When dealing with single tooth restorations, this is no big deal. However, when scanning across an arch of implants with few or no teeth present, this can be a problem.
Unless you have been hiding under a rock, you have most likely seen implant cases involving scan bodies that look somewhat like dominos. These are used with photogrammetry scanners. Similar to how your smartphone camera scans a QR code, these scanners (eg, PiC dental, iCam4D) capture the domino-like flags on the scan bodies using a very small number of images. Research has demonstrated that cross-arch discrepancies with traditional IOS scans averaged approximately 100 microns, whereas cross-arch discrepancies with photogrammetry devices averaged only approximately 20 microns. Now, that may not sound significant, but remember, with hybrid restorations, we are dealing with very small screws that measure 1 mm in diameter. Being off by 10% can really throw the case off.
Using photogrammetry and design software from exocad, I can provide an implant-supported hybrid prosthesis digitally in just three appointments: scanning, delivery of a PMMA temporary hybrid prosthesis, and delivery of the final hybrid prosthesis. The exocad software really makes the entire process easier. I scan the patient's soft tissue with an intraoral scanner and capture the implant positions with one of those photogrammetry scanners, then I put everything together in exocad. I can scan the patient's temporary prosthesis in the mouth and use exocad's amazing "best fit" matching feature to ensure that the final restoration requires almost no adjustments. In my humble opinion, when it comes to design, there is no easier and more versatile software than exocad.
August de Oliveira, DDS
1. Delivering hybrid prostheses conventionally requires a lot of steps that may incorporate user error
2. With appropriate scanning protocols, digitally fabricated hybrid prostheses can be completed in three appointments
3. Photogrammetry can greatly increase the accuracy of scanning
4. Software from exocad is like a Swiss Army Knife for digital dentistry that allows me to digitally mount the case, get models if I want them, and produce a great design