As has been discussed in previous posts, many options exist for implant abutments. One of the most recent abutment designs is the "two-piece" or hybrid implant abutment. There are many benefits that a custom hybrid/two-piece implant abutment can have over a custom zirconia abutment.
- Achieves a high strength due to the metal-metal internal connection into the implant and the metal / titanium insert or base internally supporting the abutment.
- Enables a small dental laboratory or the clinician themselves to fabricate custom implant abutments without having to outsource for the milling of the zirconia.
The abutment consists of a metal base that can purchased (ie. Ti base) or purchased and adjusted (titanium abutment) (Figure 1).
Over the top of the metal base, an all-ceramic piece is fabricated and bonded to the abutment (Figure 2).
The all-ceramic segment is typically made out of e.max or zirconia. The all-ceramic segment is then bonded to the metal base using resin cement, which is typically done in the laboratory. The research shows that the two-piece abutments are stronger than one piece zirconia abutments and that as long at the guidelines for the chimney height of the metal is followed, the retention of the components with resin cement is not a factor.
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So why the word of caution regarding hybrid implant abutments?
One contraindication for the use of a hybrid abutment would be a situation in which the Ti base is too short relative to the height of the abutment (Figure 3).
This would mainly be seen with implants that are placed too deep or on implants that have a lot of soft tissue thickness above the bone. With either clinical situation, the ceramic portion of the abutment portion that would provide the support for the restoration would be significantly weakened as it is unsupported by the metal base. This is especially evident if the ceramic portion is fabricated out of e.max. If a hybrid abutment were to be used in this situation, it would either need a taller chimney – increased height of the Ti base itself – or a taller collar, thereby placing the existing chimney height more coronal with respect to the margins of the ceramic portion.
(Click here to learn more about tissue affecting implant abutments.)
Another contraindication would be in clinical situations in which a dentist finds a surrounding bony profile that is “funnel” shaped. This bone profile is common with bone-level internal connection designed implants, as opposed to the traditional flat-top external hex-style implants where the bone is remodeled down to the level of the first thread. With the “funnel-” shaped bony profile, the flare of the implant abutment/restoration can bind with the bone thus preventing the restoration from fully seating. This can lead to things such as screw loosening, peri-implant inflammation and pressure necrosis of the bone. In these situations it is necessary to reduce the flare of the abutment/restoration so that it is narrower upon its immediate emergence out of the fixture. Although this seems easy enough to do with the Ti base on the hybrid abutment, it must be remembered that the manufacturer has set forth guidelines that the hybrid abutments need to follow for strength and predictability (Figure 4).
If the flare of the Ti base is narrowed, the resultant thickness of the ceramic portion coronal will also be thinned, thereby resulting in a structurally compromised abutment due to the weakness of the ceramic in this area if e.max were to be used. To remedy this situation, either zirconia can be used as the ceramic portion of the abutment or a different abutment design can be used altogether.
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In Figure 5, note the difference in implant depth relative to the crest of the bone for the two fixtures. A hybrid abutment can safely be used on tooth #29 since the head of the implant is coronal to the bone crest. The implant on #28 is positioned below the crest of bone. Utilizing a traditional Ti base/hybrid abutment is contraindicated in this situation as the flare of the Ti base would impinge on the surrounding bony profile. The provisional restoration that is in place on #28 (outlined due to lack of radiopacity of the material) shows the narrow emergence profile that was created. This type of emergence profile could not be reproduced with a hybrid abutment without significant structural compromise.
Although the design and use of the hybrid abutment has been a great stride in abutment selection, it must be remembered that it cannot be used in all clinical situations.
1. Comparison of fracture resistance of pressable metal ceramic custom implant abutments with CAD/CAM commercially fabricated zirconia implant abutments Kim S, et al. J Prosthet Dent 2009 Apr;101(4):226-30
2. Retentive strength of two-piece CAD/CAM zirconia implant abutments Gehrke P. Clin Implant Dent Relate Res 2013 Mar 25 (Epub)
(If you enjoyed this article, click here for more by Dr. Gregg Kinzer.)
Gregg Kinzer, D.D.S., M.S., Spear Faculty and Contributing Author