Custom Implant Abutments

However, for those less-than-ideal cases, custom implant abutments are a fantastic option. They give technicians the ability to create an ideal emergence profile that promotes healthy tissue development and to place margins uniformly below the gingiva. In addition, the use of a custom abutment allows corrections to be made in angulation with anatomical structure for better support and crown retention.

Every technician knows how labor-intensive traditional crown-and-bridge fabrications can be. Each case is unique and requires individual attention from model making to waxing and casting, and to layering, staining, and glazing. Custom implant abutments are just as unique and often are even more challenging from a design perspective.

Just as CAD/CAM technology has brought efficiencies in design and manufacturing processes for crown-and-bridge fabrication, it is doing the same for custom implant abutments, so much so that many custom implant abutment solutions are now selling for less than the traditional stock abutments.

Many dental laboratories have invested in scanners and CAD software to design substructures and full-contour restorations. Individual design control, improved fit, faster turnaround time, and reduced outsourcing expenses have become proven benefits of the digital workflow. Most laboratory model scanners are sold with crown-and bridge-restorations in mind. However, laboratory owners and technicians are beginning to realize that their scanner can also enable them to provide their own custom implant abutments solutions.

CAD/CAM-based custom abutments are available in three material configurations: all-titanium, all-zirconia, and titanium-zirconia hybrids. Given its strength, ease of milling, and lower cost, all-titanium is a very common choice. Additionally, some manufacturers offer optional special coatings such as gold nitride to enhance the esthetics of the final restoration.

All-zirconia custom abutments have become very popular. Initially only available in a bleach shade, manufacturers are now offering a variety of base shades for all-zirconia abutments. Base shading of the abutment can really make the difference when it comes to the final esthetics of the restoration. Another benefit to all-zirconia abutments is the option technicians have to use pink porcelain directly on the abutment to fill in
missing gingival tissue.

Titanium-zirconia hybrid abutments are a unique configuration. They have a titanium interface for the implant plus a cylinder to cement to a custom-milled zirconia abutment “topper,” very similar to the cast UCLA abutment concept (Figure 1). This type of abutment can provide the mechanical reliability of a titanium-to-titanium interface with the esthetic advantage of a shaded zirconia abutment. Typically, this is only an option for bone level platforms; otherwise, the titanium-zirconia margin may be visible. Extra space is also needed for this type of abutment to accommodate the titanium collar—at least a minimum thickness of 0.5 mm of zirconia and room to contour a margin for the final restoration. Laboratories and milling centers with zirconia milling capability are able to create these abutments in-house.

Every implant manufacturer would prefer to be the sole supplier of stock and custom implant abutments. For years, laboratories have been modifying stock abutments, and casting their own UCLA abutments, usually with parts from the implant company. Today, a number of third-party companies offer stock abutments and parts compatible with the factory implants.

Some implant manufacturer representatives claim that implant warranties become null and void when a third-party abutment of compatible hardware is used. It is tough to say if this position has legal legs to stand on. It becomes even more ironic as a number of implant manufacturers are now offering custom abutments and parts that are compatible with other manufacturer’s implants.

Companies such as Dentsply Implants North America (Astra Tech), Custom Milling Center, GC Advanced Technologies, and Glidewell offer an
assortment of titanium and zirconia custom abutments compatible with many of today's common implant platforms. Apex Dental Milling, B&D Dental, and a number of other milling centers offer milled-titanium abutments and hybrid abutments.

The choice between using factory parts or third-party parts is one that should be made by the laboratory and clinicians involved with the case. Laboratories outsourcing abutments should clarify who is the supplier of the abutment parts with their outsourcing partners.

Straumann and Biomet 3i now have digital impression integrations that allow the dentist to scan the patient’s mouth using the Lava™ C.O.S. (3M ESPE, www.3mespe.com) or an iTero™ (Align Technology, Inc., www.aligntech.com) and directly send the case to the laboratory. For other cases from traditional impressions, the laboratory must still pour the model and the cases must be scanned with a model scanner.

Manufacturers such as GC Advanced Technologies, CMC, and Glidewell accept cases and models directly from laboratories—scanning, designing, and milling the abutments at their facilities. Manufacturers such as Nobel Biocare and Straumann offer their own laboratory model scanners. Laboratories can scan cases, design their own custom abutments, and submit the case to Nobel Biocare or Straumann for milling of factory custom abutments.

3Shape and Dental Wings offer open-architecture scanners with optional abutment design modules. A laboratory or milling center with one of these scanners and the abutment module software can scan the model, design the abutment, and electronically send the abutment design to Biomet 3i, GC Advanced Technologies, CMC, Glidewell, or other outsource providers for milling. Biomet 3i provides factory 3i abutments. Any other implant platforms from these manufacturers are considered factory-compatible parts.

Typical laboratory workflow is conceptually the same even though scanners and CAD software may vary among manufacturers. The challenge in scanning custom abutment cases is accurately identifying the position of the implant. Even though today’s scanners are very accurate, they have difficulty scanning the area inside of the analog on the model to properly gauge depth, position, and angulation. The solution is to place a scan locator or scan abutment in the model analog and then scan the model. Figure 2 shows a scan locator for a Zimmer implant abutment in tooth position No. 30. The CAD software will use the flat surface on the scan locator to calculate the location and orientation of the analog in the model. Figure 3 shows a scan locator for a Nobel Replace abutment in the place of tooth No. 9 within the abutment design module of a popular CAD software program.

At this stage, for scan-only business models, the case could now be submitted electronically for the manufacturer to design and mill the abutment. Of course, the laboratory has the option to review the design prior to milling. Submitting the case electronically rather than shipping it saves the laboratory shipping time and cost and provides an overall faster turnaround time.

Abutment design modules are available for the most common dental CAD software packages. They often come with an additional upfront cost and annual maintenance fees, unless the scanner is supplied by an implant manufacturing company.

The design tools for abutments are very similar to those for crown-and-bridge. Scaling and positioning tools are used for large adjustments (Figure 4). The abutment can be stretched or moved in any direction necessary and waxing and morphing tools allow for contouring the abutment. There are also tools to adjust the position of the abutment margin and emergence
profile (Figure 5).

Most laboratory CAD programs support concurrent design of the custom abutment and the substructure or full-contour restoration. The benefits are three-fold. This allows for concurrent manufacturing of the abutment and coping/full-contour restoration, speeding up case processing time. It also allows the designer to take into account the shape and position of the final restoration during the design of the abutment. Finally, it bypasses the need to re-scan the case for the coping/full-contour restoration design, as scanning abutments can be time-consuming and very technique sensitive.

Custom abutments give technicians more control over esthetics and support. They give technicians yet another opportunity to design and build cases for success from the beginning. Watch for more dental CAD programs to offer custom abutment module integrations with both factory and factory-compatible implant manufacturers. Custom implant abutments are already a growing market segment for most dental laboratories. It is a trend that does not show any signs of slowing.

Chris Brown is the manager of Apex Dental Milling in Ann Arbor, Michigan.