Hybrid abutments: The first TEAM talk by EADT eV took place on October 20th and highlighted the topic of “two-part abutments” from all sides. The new interactive online format serves the targeted exchange of knowledge. The TEAM talk lives from the participation principle. The participants are not just passive listeners, but can also actively participate. The entertaining online talk is moderated by Carsten Fischer.
The focus of the first TEAM talk was on three central questions relating to two-part abutments (hybrid abutments), which were discussed and discussed together with the participants. We summarize some of the key statements here for further reading. You will often find further links to relevant articles. These contain references to scientific studies and publications.
Hybrid abutments: Two-part abutments – question and conclusion
1. Are the hybrid crown and the hybrid abutment plus crown equally safe?
Two-part abutments (hybrid abutments) consist of two parts - usually made of different materials - that are connected to each other. They consist of a titanium adhesive base (Ti-Base) and an associated structure. Structures made of zirconium oxide are mostly described in the literature. The titanium adhesive base creates a known metallic screw connection between the titanium implant and the abutment. The structure/cone is usually made individually from zirconium oxide. This makes it possible to use tooth-colored materials as abutment material, especially in the aesthetic zone.
Studies (e.g. Wolfart et al., 2006) showed good bonding possibilities with ceramic materials such as zirconium oxide. Eschbach et al. (2007) examined the adhesive bond and the adhesive joint. Adhesive joints with a gap of 30 μm showed significantly higher adhesion values than adhesive joints with a gap of 60 μm.
Thanks to digital CAD/CAM manufacturing in the manufacture of the structure, small gap dimensions can now be created. The connection between the ceramic structure and the titanium adhesive base is created by an adhesive attachment. This bonding should be carried out using a bonding protocol according to the manufacturer's instructions. A precise fit and a validated Adhesive protocol of titanium base and abutment lead to a high bond strength of the adhesive connection (Gehrke et al). Sailer et al. showed similar fracture loads of titanium/zirconia based hybrid abutments with a small diameter (implant diameter 3,3-3,5 mm) compared to conventional titanium abutments. Meyer R (2009) examined the size of the adhesive surface in relation to the pull-off force.
The overall strength increases with the vertical height of the titanium base. The adhesive surface should have a height of at least 4 mm and an adhesive surface of at least 35 mm2 exhibit.
From the perspective of current literature, hybrid abutment crowns and hybrid crowns are equally safe in terms of bonding if the size of the bonding area, a validated bonding protocol and the gap dimension of the bonding joint are adhered to. The importance of extraoral bonding was also emphasized in the discussion.
2. How should the metallic adhesive base be prepared and which properties of the adhesive are necessary for success?
The titanium base and the structure are permanently attached adhesively. It is crucial that the areas to be bonded are cleaned and enlarged in the first step. Corundum blasting using aluminum oxide (microretentive composite) has become established. Aluminum oxide with an average particle size of 50 µm is often chosen. The surface should be blasted at an angle of 45° and a distance of 10 mm. In the second step, the surfaces are conditioned using primer/silane. The expiry date of the adhesive system should be strictly observed. If the liquid is milky, the primer/silane should no longer be used. A distinction can be made between one- and two-bottle silanes. In the one-bottle systems, the hydrolysis has already been carried out. These materials have a shorter shelf life than two-bottle systems in which the user first hydrolyzes/activates the silane by mixing the two liquids. It is important that the adhesive system is coordinated with the luting composite; Here it makes sense to stick with one manufacturer, as mixing products from different manufacturers can have a counterproductive effect.
3. Are two-part abutments a safe care concept?
The TEAM talk discussed, among other things, the question of “screwed vs. cemented”. There is a great desire for a simple care concept for fixed implant restorations. By using monolithic ceramic materials for implant restorations, the titanium adhesive base can be seen as a connecting link between the implant and the crown/abutment. The bonding creates the mechanical connection between the implant structure (Ti base) and the restorative material.
For the occlusally screw-retained hybrid crown, the height of the titanium adhesive base must be set in relation to the crown length. As already mentioned in question 1, the size of the adhesive surface plays an important role. Different implant manufacturers offer different heights of adhesive bases. The higher the titanium adhesive base, the greater the deduction value. For screw-retained implant restorations, the screw opening should be in the occlusal area for posterior teeth and in the palatal area for anterior teeth. Through the possibility of Angulation of screw channels, occlusal openings can be optimally positioned even with difficult angulations.
The advantage of the screw-retained implant-supported reconstruction compared to the cemented implant crown is that it is easy to remove, as is the case e.g. B. may be necessary in the case of ceramic fractures or screw loosening. In addition, during insertion, the pressure on the tissue can be gradually adjusted by slowly tightening the occlusal screw.
The discussion at the EADT TEAM Talk also highlighted the biggest disadvantage of occlusally screw-retained implant crowns/bridges (especially with implant connections secured against internal rotation). If the insertion direction of the implant axis in single crowns does not match the insertion direction of the approximal contact points, this makes insertion more difficult. Large interdental triangles are usually created unintentionally. This makes it difficult to control the exact fit of the implant connection of the hybrid crown.
Cemented, implant-supported superstructures can be used if the position of the future screw channel is unfavorable due to the prosthetically incorrect implant axis. In the case of cemented connections, cement residues remaining in the sulcus are seen as a possible trigger for peri-implant diseases (Wilson 2009). Linkevicius et al. were able to show that the increasing subgingival position of the crown margin is associated with increased remaining cement residue (Linkevicius et al. 2013). In this context, it should be mentioned that most studies use standardized, prefabricated abutments. Individual abutments enable an equigingival position of the crown margin and thus a reduction in subgingival cement residues.
Cemented implant crowns and bridges are easier to insert than screw-retained ones in terms of the approximal contact point. Due to the conical stump preparation (4-6 degrees) of the abutment, the direction of insertion has a higher variance.
The disadvantage of cemented implant restorations is the inability to remove the crown. This is necessary in the event of screw loosening or fracture, as well as in ceramic fractures/veneering fractures, so-called chipping, one of the most common technical complications of ceramic implant restorations (Schwarz et al. 2012). In most clinical cases, these crowns must therefore be trephined and thus destroyed in order to reach the screw channel and unscrew the crown.
The discussion showed that two-part abutments represent a safe care concept. The assessment of a biological complication of the adhesive gap was unclear. The precision of the gap size of the adhesive joint, the quality of the adhesive bonding of the titanium adhesive base and abutment/crown and the size of the adhesive surface have the greatest influence on the success of two-part abutments. The EADT TEAM talk showed the importance of the selected technology.
The relationship between the adhesive surface of the titanium adhesive base and the crown structure/crown length in particular leaves scientific questions unanswered.
EADT eV statement
- The patient's wishes always come first when choosing materials. The implant prosthetic work team should discuss the options together. Teamwork makes it possible to pool expertise.
- When adhesively fastening, the manufacturer's instructions should always be taken into account and the materials used should be coordinated.
- Bonding of the titanium adhesive base should always be carried out in the laboratory.
- The selection of “bonded/cemented” should always be made on a patient-specific basis (e.g. closure of the interdental spaces and position of the implants).
- The use of original implant parts should be given preference.
The next TEAM talk will take place on December 15th at 17.00 p.m. with the topic “Zirconium oxide”. We are already looking forward to the next round!
Reading tip EADT eV: Dental preparation and cleaning procedures for implant abutments