Digitally Driven Surgical Guide Planning

In the laboratory, it is possible to do what is called a double scan: Scan a denture with a desktop scanner followed by scanning the model. As long as the model doesn't move, the scanner can scan the denture and the model in perfect relationship to one another. Using 3Shape Implant Studio (3shape.com), the laboratory technician can "stitch" together both pre-preparation scans and preparation scans.

The same technique and workflow can be utilized by the dentist chairside using an intraoral scanner. This allows the dentist to attain all the information necessary for the laboratory while providing convenience for the patient by reducing the number of appointments and eliminating trips to multiple facilities. However, the chairside technique requires that landmarks are captured on both scans. If the patient is wearing the denture, the entire palate is covered, making it difficult to capture the landmarks and challenging the ability of the dentist to align and stitch both scans. This article discusses and provides a chairside scanning protocol to ensure accurate and efficient double scanning extraorally for in-laboratory design of the surgical guide.

The chairside protocol requires that the dentist choose something to use as a base (Figure 1) and create a model of the edentulous area using alginate or PVS impression material. In order to stitch the model's information to the CT scan data, the dentist must place radiopaque stickers with scan markers around the denture (Figure 2) and scan the denture on the model made of alginate or PVS impression material (Figure 3). Using the 3Shape Trios, the dentist sets up the scan order to allow a pre-preparation or pre-op scan and then scans the denture and all its surrounding borders as a pre-preparation scan (Figure 4). Following that, the dentist scans the tissue surface, which is represented in the alginate or PVS impression model, where all the landmarks were captured (Figure 5). Since all the pertinent landmarks were captured in both scans, the software can align the two scans in perfect relation (Figure 6), similar to the technique used with a laboratory desktop scanner. From there, a CBCT scan (with DICOM file output) can be taken of the patient with the markers still in place, as the markers indicate precise points to stitch in the design program.

Once all of the proper data is captured, it is sent to the laboratory for implant surgical planning and surgical guide design (Figure 7). The technician imports the data into 3Shape Implant Studio. (Note: Any CAD software that processes multiple scans should work with this technique.) The technician imports the data in the following sequence: First, the pre-preparation or pre-op scan of the denture; next the preparation scan, which shows the tissue; and last the CT data (DICOM file). Using the abovementioned import protocol, it is possible to stitch the scan markers that were on the denture to those markers on the CT scan. The scan markers must align perfectly, and although the software typically does a great job with alignment, it is the author's suggestion to verify visually prior to proceeding. As long as there are common "landmarks" on all scans, it is possible to stitch together the CT data and model scans.

A similar workaround may be used when scanning a patient who has a significant number of metal-based restorations, as metal creates scatter on the CT data. BlueSky Bio (blueskybio.com) offers a technique using what is called a scan appliance. All that is needed is a disposable impression tray, scan markers, and impression material. To do this, the protocol suggests the dentist take an impression of the patient's arch using conventional impression materials. (However, alginate impression material is not recommended in this protocol because it has a tendency to tear apart upon removal.) Remove the impression from the mold and clean off all excess material, including interproximal walls that may create undercuts. Radiopaque scan markers, are then placed in different areas on the plastic tray, carefully so they are not placed too linear or close in proximity to one another. The scan appliance is then placed on the CT scanner and scanned as though the patient were being scanned. (Impression material registers perfectly on a CT scan.) Once the appliance is scanned, it is placed back in the patient's mouth and scanned again. This provides the perfect relation from the scan appliance to the mouth. The scan data files are imported into BlueSkyBio using the option "Import Scan Appliance." The scan appliance is stitched by connecting the impression markers to the scan markers seen on the CT output file. The program will prompt the user to choose a path of insertion and crop the scan appliance. The software will then create a positive scan, which allows the laboratory to continue with implant planning.

Digital dentistry has opened the door to so many new concepts and techniques, some previously unimagined. Both digital solutions shown here are effective and help eliminate the need for a radiographic stent, thus lowering costs for the dentist, the oral surgeon, and, ultimately, the patient. Technological advances in dentistry are progressing at a staggering rate, but it is how we as dental professionals use this technology that allows us to explore its possibilities and get great results.

Acknowledgments

The author would like to thank John Vargas, DDS, at Chappaqua Smiles in Chappequa, NY, and Benjamin Kur, DDS, at Westchester Oral and Maxillofacial Associates in Hawthorne, NY, who collaborated with him on this case.

Jeffry Tobon, CDT
Founding Executive Director
DesignLab Dental Inc.
Westbury, NY