Part 2: The Road to Implant Abutments
Where custom CAD/CAM abutments come into their own
The following is a continuation of an article that appeared in the June issue of Inside Dental Technology.
Three Strategies of Implementing Abutments by CAD/CAM
Three different fabrication methods for CAD/CAM abutments can be distinguished at the present time:
• Complete outsourcing (e.g., AstraTech Atlantis).
• CAD in the laboratory, CAM in the milling center (e.g., Straumann Wax Abutment, Straumann Cares, Bego Medical).
• CAD in the laboratory, CAM in the laboratory (e.g., KaVo Neolink, Sirona zirconia bonding abutment).1
1. Complete Outsourcing
Examples of complete outsourcing of implant abutments include Astra Atlantis (Astra Tech, Mölndal, Sweden) and abutments supplied by the Compartis ISUS milling center (DeguDent, Hanau, Germany). This implementation strategy will be outlined using the Atlantis system (Astra Tech) as an example. The first step after fabricating the implant model (Figure 1) is to create a wax-up. The adaptation of prefabricated teeth has proved to be highly efficient for this purpose. To achieve optimal positioning of the teeth over the implant analogues on the cast, they can be waxed up to length-reduced impression posts for reproducible placement and removal (Figure 2 and Figure 3). The abutments are defined and ordered through a Web-based form. A number of design features for the CAD/CAM abutment to be customized can be entered. These include parameters such as transmucosal profile, preparation depth as measured from the gingival margin or implant shoulder, shape of the abutment preparation (chamfer or shoulder), any retention surfaces in the case of titanium abutments and any parallelism between abutments if desired. With regard to mucosal shaping, for example, these four design options are available:
• Mucosa will not be shaped.
• Mucosa will be supported.
• Mucosa will be shaped.
• Maximum anatomical width.
A parcel service takes care of collection and delivery. Delivery of titanium abutments is guaranteed within five days; delivery of zirconia abutments within seven days. Orders of more than three abutments will delay the shipment by one day per additional unit. The customized abutments are fabricated based on the existing wax-up in the milling center. Astra Tech’s patented software solution Atlantis VAD (Virtual Abutment Design) permits matching the abutment design to the definitive external geometry of the restoration. The resultant design will greatly facilitate the subsequent task of creating the framework and veneer back in the laboratory. Framework errors are virtually ruled out by this procedure. Once the abutments have been designed, screenshots are sent by email for verification. In early 2010, a service was introduced that allows technicians to verify and check the CAD abutments with a 3D viewer. The go-ahead for the actual fabrication process is also given by email.
A collaborative effort by 3M ESPE and Astra Tech has resulted in a new approach based on the Lava Scan ST system. After scanning laboratory-fabricated implant models with this system, the data captured are transmitted directly to the milling center. This new procedure enables laboratories that use Lava Scan ST to place orders without having to ship a model to Astra Tech (Figure 4 and Figure 5).
Another collaborative effort by Astra Tech and Dental Wings (Montreal, Ontario, Canada) has been under way since early 2010. A similar principle as with the 3M ESPE scanner is used as data from the Dental Wings 3D scanner can be directly transmitted by electronic means to Astra Tech’s design and milling center for fabrication of Atlantis abutments. Atlantis abutments are available with interfaces for different implant systems (Astra Tech, Nobel Biocare, Straumann, 3i, Lifecore, Zimmer Dental, Biohorizons, Innova, and Sterngold). They are offered as zirconia, titanium, or GoldHue (titanium nitride-coated titanium) abutments (Figure 6 and Figure 7).
2. CAD in the Laboratory, CAM in the Milling Center
Another way of obtaining CAD/CAM abutments is to perform the CAD (i.e., the design) part in the laboratory and then to transfer the data to a milling center electronically for fabrication of the customized abutments with industrial milling systems based on the data record from the laboratory. Two different techniques are available to generate the CAD record:
• Creating a wax abutment.
• Designing the abutment by CAD only.
2a. Wax Abutment
This option is currently available, for instance, with the Straumann CAD/CAM system. The Straumann Wax Abutment will serve as an example to outline this implementation strategy. Wax-up sleeves are used as basis for the wax abutments. These sleeves facilitate the task of waxing up the abutment geometry; in addition, they also serve as connection element to the scan mount in the Straumann ES-1 Scanner (Figure 8, Figure 9, and Figure 10).2,3 Upon completion of scanning, the system will generate a CAD record of the wax-up. Subsequent modifications to the design such as smoothing of surface irregularities can be performed (Figure 11). Finally, the data record is transferred to the Straumann milling center (Leipzig, Germany) for fabrication of a monoblock (i.e., without a bonding base) abutment. Advanced HSC (high-speed cutting) systems are available at the milling center for this purpose. The implant-abutment interface being a prefabricated component, only the external abutment surface needs processing. Zirconia abutments are fabricated from a hot isostatically pressed (HIP) material that offers superior mechanical properties due to industrial-grade sintering (Figure 12 and Figure 13).
2b. Straumann Cares and Straumann CAD/CAM Abutments
This version of implementing CAD/CAM abutments involves a CAD record generated in the dental laboratory, which is then electronically transferred to the Straumann (Cares or CAD/CAM) milling center. Cares or Straumann CAD/CAM abutments are designed with Cerec 3D (Figure 14, Figure 15, and Figure 16) or Etkon Visual (version 5.0 or later) software, respectively. CAD-based manipulation tools for abutments include rotation, scaling, and translation. It is also possible to add and subtract material. The software ensures that predefined values for minimum wall thickness are respected. Sirona Cares, for example, outlines the minimum thickness in blue while the implant screw channel is displayed in red. The same principle of electronically transferring the CAD record to the milling center once the design part has been completed also applies to the Straumann (Cares or CAD/CAM) system. The process involved corresponds to the wax abutment process.
3. CAD in the Laboratory, CAM in the Laboratory
The third possibility is to conduct the entire fabrication process for custom CAD/CAM abutments in the dental laboratory. Titanium bonding bases are used for this purpose. The abutments milled from zirconia are bonded to these bases.1 The blanks are custom-milled in a pre-sintered condition and therefore need to be densely sintered after milling. The following two solutions are available to fabricate the zirconia abutments:
3a. Conventional Zirconia Blanks
Here the zirconia abutment is milled from a conventional zirconia blank, such that the milling system will also take care of creating the screw canal. Examples include:
• Titanium bonding bases by Medentika (Hügelsheim, Germany) of the 800 series in combination with an add-on module (nt-IQ by NT-Trading, Neustadt, Germany) for 3Shape Dental Designer. Scan bodies and bonding bases are available for numerous different implant systems.
• Titanium bonding bases by NT-Trading (Neustadt, Germany). Scan bodies and bonding bases are available for numerous different implant systems.
• Titanium bonding bases by Camlog are complemented by Camlog scan bodies (introduced in June 2010) to be used in dental CAD systems.
• Titanium bonding bases, scan bodies, and blanks (inCoris ZI meso) by Sirona are available for seven additional implant systems.
3b. Semi-finished Zirconia Blanks
Here the zirconia abutment is fabricated from a semi-finished blank. For this purpose, manufacturers are offering partially prefabricated blanks with the connection geometry of the bonding base already incorporated. All that remains to be done is to customize (by grinding/milling) the external surface to the desired shape. The blanks are milled in a pre-sintered condition and therefore need to be densely sintered after milling. To name two examples of semifinished zirconia blanks:
Sirona bonding bases, scan bodies, and (inCoris ZI meso) blocks are available for seven additional implant systems.
Most of the manufacturers listed use an anti-rotational mechanism of the interface between the titanium base and zirconia abutment, which ensures that the abutment will not rotate out of position to avoid incorrect bonding to the titanium base (Figure 27). Overly tight seating of the abutment on the bonding base may be caused by interferences in the area of the anti-rotational mechanism, which can be precisely removed with a diamond cutter.
The CAD process for abutments offers customary manipulation tools such as scaling, rotation, translation, and adding/reducing material. Sirona Cerec/Sirona inLab introduced a CAD process for abutments in software revision V3.0. KaVo Everest has offered CAD/CAM abutments ever since version 3.x of the Energy software package was released. 3Shape Dental Designer is already capable of accommodating 11 different implant systems with the help of an add-on module (nt-IQ by NT-Trading) as well as scan bodies and titanium bonding bases (NT-Trading and Medentika). This option is supported, for instance, by the Bego CAD/CAM and 3M ESPE Lava systems.4
The Heraeus Cara system has offered this option since the second half of 2010. The bonding abutment is designed in the laboratory (3Shape Dental Designer, Lava design 5.0). The data record is then transferred to the milling center, where the bonding abutments are fabricated and shipped back to the customer. Bego Medical currently offers zirconia (BeCe CAD Zirkon+, available in five shades; BeCe CAD Zirkon XH offering higher strength, available in three shades), CoCr (Wirobond C+) and all CAD/Cast materials for bonding abutments. In addition, Bego also offers to fabricate copings that will match the bonding abutments.
The success of implant-supported restorations depends on a number of separate factors. One of these factors (alongside others such as bone situation, implant position, implant length, and oral hygiene) is the abutment to be used with the implant. In many situations, prefabricated abutments will run up against limitations that will bring about dissatisfying outcomes. This is where custom CAD/CAM abutments come into their own.3 They can be optimized in terms of axial inclination and shape for existing situations. The most important clinical benefit of these abutments is their ability to shape the emergence profile. Used with cementable restorations, they eliminate any need for the tricky job of removing excess cement because the restorative margin can only be placed at (or slightly above) the gingival level. The effort of going into manual procedures remains within economically acceptable limits, and the materials used can be processed in a conservative fashion, which is not always the case with manual surface treatment of customizable abutment blanks. It is therefore not surprising that more and more implant manufacturers and CAD/CAM suppliers should join forces to provide their customers with the option of obtaining CAD/CAM abutments. These very positive developments will offer advantages for dentists and technicians. Most importantly, they will also benefit the patients.
The complete article originally appeared in 2011 in EDI Journal as “Roads to Implant Abutments.”
The techniques and uses described in this article do not necessarily comply with US federal rules, approved uses, and regulations regarding these products.
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3. Blatz MB, Bergler M, Holst S, Block MS. Zirconia abutments for single-tooth implants – rationale and clinical guidelines. J Oral Maxillofac Surg. 2009;67(11 Suppl):74-81.
4. Hannker C. Individuelle Abutmentgestaltung. Zahntech Mag. 2010;14:16-27.
5. Lüppens F. Individuelle Abutments aus Zirkoniumdioxid: CAD/CAM-gefertigt oder individualisiert? Digital Dental News. 2009;3:20-24.