Inside Dental Technology
March 2012, Volume 3, Issue 3
Published by AEGIS Communications
Make it Simple
Take advantage of insertion and verification tools for implant reconstruction and bridges.
The patient presented with a total of seven implants in the upper jaw from different implant systems. Two of the implants were placed several years ago and were restored with a 3-unit screw-retained bridge, which would later facilitate the matching of the esthetics. Many problems with implant cases often arise at the beginning.
Trusting the Impression
Normally, in the larger cases time, material, and money are wasted because the framework does not fit or the design is incorrect. In either case, the patient must be rescheduled. This can happen in spite of available modern digital tools and techniques.
In the presented case—after mounting, diagnostic wax-up, and index—the technicians made custom abutments on a fixture-level impression, prepared acrylic insertion tools for the abutments, and then produced a zirconia-milled bridge framework. The dentist placed the abutments and tried to seat the framework, but unfortunately it did not fit. Either the impression or the model was not 100% accurate.
Had this bridge been cast in metal instead of zirconia, the technicians would have been able to cut and solder it. Considering the price of gold and casting problems for large-span bridges, zirconia was chosen. Even though zirconia offers the perfect alternative to gold, the technicians need to find a way to adjust the fitting.
Solving the Problem
A tool or guide needs to be created to ensure precision from the beginning to help the technicians communicate with the dentist better and perhaps prevent future problems. The instrument should allow for faster and perfect results, streamlining efficient production for the entire restorative team. It does not matter whether the restoration is fixed or removable—the workflow is almost the same.
Because the first model was incorrect, the technicians asked for a new impression. From this, a master model was created to make a new superstructure. The original custom abutments were placed in the new model, and the models were mounted on the Artex® articulator. The Ceramill Map 300 scanner from Amann Girrbach—unlike many other scanners on the market—has the advantage to insert fully articulated models into the scanner, producing a virtual articulation on the screen. The abutments were then scanned with the Ceramill Map 300.
After scanning the master model, antagonist model, and articulation, Amann Girrbach provides a very useful transfer process. The scan now appears fully articulated on the computer screen for the technicians to begin their design. Another advantage of the Ceramill Mind software from Amann Girrbach is that technicians could now scan other cases before beginning the current case.
Setting up the preparation lines is the first step the technicians should follow (Figure 1). The settings can be prepared next for block-out, setting up the cement gap, and margin-angle. Parameters can be preset specifically for each client or case type. Then the final path of insertion is adjusted, and with Ceramill Mind, the technicians are able to use individual paths of insertion as needed.
This is followed by the orientation of the anatomical tooth shapes (Figure 2). These are stored in a library and can be modified individually when needed. When all of the crowns are designed, the software calculates the actual size of the restoration. At this stage, further anatomical modifications can be made using different tools. Technicians can cut, add, smooth out, pull, or push whole tooth areas.
Next, the actual restoration will need to be designed. A framework should be created for the dentist to use as an insertion tool for the custom abutments that can also be used as a verification jig for the final zirconia framework. This way the technicians only need to scan and design the restoration once, and the framework can be produced in the final shape. Before milling, the Ceramill Mind gives the technician two options. The first option allows the technician to design the full anatomical shape so that the dentist can try in and check the esthetics immediately and make any necessary changes. The second option allows the technician to reduce the framework by the optimum thickness needed for porcelain veneering.
The technician is now able to specify how many millimeters the veneering material should be, and he can also design certain interproximal areas for the perfect support. From experience, the biggest risk of chipping in the interproximal area is the thickness of the veneering porcelain. To avoid this, the technician will leave interproximal contacts in solid zirconium oxide—this can be hidden by proper staining and veneering.
In this case, the technicians chose the reduced form and designed the framework to full contour. Using the shrinking function, the whole framework was reduced by the chosen dimension for veneering porcelain. After shrinking the framework, it was possible to change the custom design with the same design tools that were originally used (Figure 3, Figure 4 and Figure 5).
Now that everything was saved as designed, the nesting could begin. PMMA milling blanks were used for the provisional frameworks. An appropriate blank that had an appealing color and enough stability was used. This material is much more affordable than zirconia—a factor not to be overlooked. The software gave technicians absolute freehand when nesting. The blanks were given names, which was very useful for reusing it again until there was no material left to mill.
Milling was now ready using the Amann Girrbach Ceramill Motion milling machine. This is very easy to use, extremely quiet, and has a strong suction. The blanks are easy and quick to assemble manually. For the milling process, each unit can take approximately 10 minutes.
During the milling process, a status report was provided for the time remaining, the tool wear, and maintenance status. After the Ceramill Motion milled the bridge from the provisional materials, the technician broke the framework from the blank (Figure 6 and Figure 7). The connector sprues were trimmed and the framework was tried on the model for perfection (Figure 8 and Figure 9). Then holes were drilled in the area of the abutments in the framework so that it could be used as the seating tool for the abutments (Figure 10). The framework was then sent to the dentist for a try-in.
After the framework was perfectly fitted in the mouth, the case came back to the laboratory.
Using the Ceramill Mind, the technicians recalled the original design file used for the seating tool, and nested the framework to a zirconia blank. Once the nesting was successful, the framework was automatically milled.
Once milling was complete, the framework and the sprues were removed from the blank. Color was then added to the framework followed by sintering in the Ceramill Therm furnace. This process took about 10 hours because of the slightly bigger span of the bridge to avoid deformation. This is can be done overnight. The technicians do not recommend the much quicker microwave sintering because of the risk for micro-cracks. The Ceramill Therm furnace turns off automatically after a successful sintering. The next morning, the framework was removed, inspected, and checked for fit. The final step was to apply veneering porcelain, which greatly varies among each laboratory’s technique.
The authors would like to thank Amann Girrbach and Dr. Carlos Garcia with his patient.
Klaus Lampmann, CDT, FIADIT, is the owner of Zahntechnique in Miami, Florida.
Alexander Wunsche is the production manager at Zahntechnique in Miami, Flordia.
The preceding material was provided by the manufacturer. The statements and opinions contained therein are solely those of the manufacturer and not of the editors, publisher, or the Editorial Board of Inside Dental Technology.