An implant abutment is the part or component that serves as support and/or retention for a dental prosthesis. The selection of the implant abutment for each individual patient case is therefore an important part of the implant-prosthodontic treatment phase. In this module, we will discuss the function of implant abutments, different implant abutment types, different abutment materials and how to select an abutment based on a prosthodontically driven process.

After completing this ITI Academy Module, you should be able to define the function of an implant abutment, identify different types of implant abutments, list different implant abutment materials and their indications, select abutments based on prosthodontic indications and planning.

An implant abutment is the implant component that serves as support and/or retention for a dental prosthesis. It is also the link between implant and prosthesis. As such its purpose is to provide a prosthodontic platform similar to that of a tooth preparation for a fixed dental prosthesis or FDP.

In a similar manner to a tooth preparation, the abutment - independent of the abutment material - must suit the requirements of the prosthesis as well as the given clinical situation. This is demonstrated in these clinical images. A titanium abutment to replace a second premolar is seen on the left. The images in the middle and on the right show the same indication - replacement of a central incisor - one with a tooth prepared as an abutment and one with an implant-supported zirconium dioxide abutment. The implant abutments need to observe consideration of the same clinical factors as routine tooth preparations. These include retention, strength, position of and access to the preparation margin, alignment with neighboring teeth or other implant abutments and spacing to ensure adequate material dimensions for the planned prosthesis. These clinical considerations are therefore reflected in the wide range of abutment designs that are available.

An abutment is also the connection between prosthesis and implant. The abutment is predominantly a separate component. This offers the advantage of flexibility in selecting an abutment that is best suited to the specific case requirements. All separate abutments have a screw-type connection to the implant. For some implants the abutment is an integral part of the implant itself but this is the exception and can limit prosthodontic flexibility. This module will concentrate on abutments that are separate components to the implant.

Function of Implant Abutments, Key Learning Points: Abutments serve as support and/or retention for a dental prosthesis. Abutments provide the connection between fixed dental prosthesis and implant. Abutments need to suit prostheses requirements. These requirements depend on the individual patient situation, type of prosthesis, and type of implant.

Abutments are designed for their prosthodontic purpose. Differences in abutment designs all have the common aim of providing prosthodontic solutions and flexibility for any given clinical situation. The notable differences in abutment types are dictated by clinical requirements. These include method of prosthesis retention; degree of precision of connection to implant; flexibility of prosthodontic platform; choice of material; and method of manufacture. These different types will now be discussed.

Abutments offer two types of method of retention. Implant-supported fixed dental prostheses can be either cement or screw retained to the abutment. The two different retention types therefore dictate the retentive characteristics of an abutment's prosthodontic platform. The abutment in the left image is designed to provide cement retention for a single-unit prosthesis. The abutment in the middle is designed for a screw-retained prosthesis. The arrow in the middle image points to the screw retention thread in the top of the abutment, while the arrow in image on the right points to the corresponding hole in the prosthesis that provides access to this screw retention thread. The considerations and indications for the two different methods of retention together with their respective advantages and disadvantages are covered in more detail in the ITI Academy Learning Module 'Design Principles for FDPs.'

Abutments offer a difference in the degree of precision fit of the abutment connection to the implant. This is a fundamental aspect of abutment design, and abutments are therefore described as being either engaged or non-engaged. The selection of an engaged versus non-engaged abutment depends on the type of fixed dental prosthesis the abutment serves. The purpose of the engaged type is to provide a precise fit of the abutment to the implant and to prevent rotation. The provisional abutment shown here has flat sides on its connection that engage corresponding flat sides inside the implant, thereby providing precise fit and preventing rotation. Engaged abutments are indicated for screw- or cement-retained single-unit prostheses and for cemented implant-supported multi-unit prostheses. A less precise and therefore non-engaged connection allows simultaneous insertion of multiple abutments integrated in a screw-retained multi-unit prosthesis. This image shows the non-engaged, tapered abutment connections in a screw-retained provisional prosthesis on four implants.

Abutments vary in their design of prosthodontic platform. This is to offer prosthodontic flexibility. The flexibility is needed for esthetic, functional, biological and spatial reasons. As seen here these can include spatial correction of discrepancies between implant and prosthesis axis, spatial compensation for limited or increased interocclusal clearance, and functional indexing for precise fit and anti-rotation for a single-unit prosthesis. The flat sides on the right and left images show the abutment indexing.

Implants are designed either with the prosthodontic platform incorporated in the implant or provided by a separate abutment. The one-piece implant on the left has an inbuilt shoulder that forms part of the prosthodontic platform, and the abutment therefore has the equivalent role of a post and core for a tooth preparation. The two-piece implant on the right finishes at bone level, and the entire prosthodontic platform is on the abutment. The abutment therefore fulfills the role equivalent to an entire tooth preparation. There is greater scope for prosthodontic flexibility when the entire prosthodontic platform is on the abutment.

Implant abutments are available in different materials. Traditionally abutments have been available in titanium or gold, but due to progress in the implant-prosthodontic field and ongoing improvements to the manufacturing processes, implant abutments can be made out of ceramic materials as well. Titanium is used as an abutment material for all prosthodontic indications, but the ceramic alternative has an advantage in esthetically sensitive areas where the titanium might cast a dark shadow through thinner mucosal tissue phenotypes. Implant abutment materials will be covered in more detail in the next learning objective.

There are two methods of manufacture of abutments - prefabricated and custom made. Traditionally implant abutments have been prefabricated, but increasingly the need for customized abutments that are specifically designed for individual prosthodontic situations has become evident. This is especially the case in the sensitive esthetic region, where the selection of the abutment might be the crucial detail that decides the final esthetic outcome. Prefabricated abutments will here be referred to as 'standard abutments.' They are available in predefined designs to serve a wide range of clinical situations. The image shows the use of a standard angled abutment for a cemented single-unit prosthesis where the angulation compensates for a discrepancy between implant and prosthesis axis. Customized abutments are individually designed and produced when there is a need for the abutment to fulfill specific case requirements. The image shows a customized zirconium dioxide abutment for a cemented all-ceramic single-unit prosthesis. In this case the abutment provides an individual emergence profile and a customized level of the margin for the cemented prosthesis.

Standard abutments are available in a range of materials. The advantages of standard abutments are simplification of the technical manufacturing phase and, therefore, production time. This in turn reduces the cost of the implant-supported prosthesis. Although the abutments are prefabricated, they are available in a wide range of designs. With angled standart abutments it is, for example, possible to correct divergences between implants supporting multi-unit prostheses. Moreover, both screw- and cement-retention types are available.

For ceramic abutments there are, however, some clinical limitations. For this type of abutment the implant must be placed in a prosthodontically correct position. This is particularly important in the coronoapical dimension, where caution should be taken if the implant is placed too apically. In spite of being available in varying heights, a standard abutment for a screw-retained single-unit prosthesis might not provide enough support for the veneering ceramic. Equally, for a cement-retained single-unit prosthesis it could be difficult to ensure access for complete cement removal at the set margin of a standard abutment if the abutment is located too far submucosally. Finally, some standard abutments only offer limited correction of divergences.

Customizing an abutment gives the clinician the freedom to individualize the prosthodontic platform in terms of position and angulation. It is, for example, possible to individualize the emergence profile and the position of the margin of the definitive prosthesis. This process also allows abutments to be designed to provide optimal support for the veneering ceramic material to reduce risk of chipping and fracture. Customized abutments are available for both screw and cement retention.

There are three methods of manufacturing customized abutments. These are lost wax, CAD/CAM, and a two-piece combination of customized and prefabricated parts. Gold abutments manufactured by lost-wax casting techniques have long-term clinical evidence. This method of manufacturing, however, is more technique sensitive and also time and cost intensive. CAD/CAM technology increasingly figures in manufacturing of abutments. CAD/CAM has the advantage of stable quality outcomes, but it carries additional costs due to the time required for the digital workflow. Two-piece combinations have a customized part bonded to a prefabricated, standard base. When the bonded part is ceramic and the standard base is titanium, these abutments offer the combined advantages of esthetics in the transition zone and strength in the connection to the implant.

CAD/CAM further offers the option of no abutment. This is a more recent development that can be applicable to multi-unit prosthodontic superstructures where an engaged connection is not required for precision or prevention of rotation. Instead, the connection is milled directly into the metal substructure. In this example of a milled cobalt-chrome substructure, the direct connection to the prosthodontic platform of tissue level implants can be observed.

The use of a two-piece combination with a customized part bonded to a prefabricated base is increasing, but the supporting literature is still limited to case series and in vitro studies. Both screw- and cement-retained options are possible, and this abutment type can be used for both single- and multi-unit FDPs as well as for in-office CAD/CAM crown procedures. Concerns about the possible soft tissue effect of the bonding gap between the customized part and prefabricated base are being addressed by the availability of prefabricated components with various options for the height of the prosthodontic platform.

Implant Abutment Types, Key Learning Points: Abutments are designed for their prosthodontic purpose. Differences in abutment designs all have the common aim of providing prosthodontic solutions and flexibility for any given clinical situation. The notable differences in abutment types are dictated by clinical requirements as reflected in: method of prosthesis retention, degree of precision of the connection to the implant, flexibility of the prosthodontic platform, choice of material, and method of manufacture.

Titanium and zirconium dioxide are the most commonly used abutment materials. Titanium is used for both standard and customized abutments, including CAD/CAM fabrication. Titanium abutments are also used for provisional prostheses. Zirconium dioxide is used for standard and customized CAD/CAM abutments. The alternative is gold, which is used for customized abutments manufactured by the indirect lost-wax casting technique. PMMA or polymethyl methacrylate and PEEK or polyether ether ketone are used for fixed implant-supported provisional prostheses.

As shown on the previous slide, titanium and zirconium dioxide are used for a greater number of clinical indications than the other materials listed. Let's compare and contrast these two materials. Titanium is the material of choice when considering its long-lasting and well documented behavior under functional loading. It has excellent biocompatibility, mechanical strength and resistance to corrosion. It is therefore the abutment material of choice for posterior sites, but may also be used in anterior sites. However, regarding the soft tissue esthetics and the overall esthetic outcome, the results for titanium abutments are less compelling. Zirconium dioxide has similar biocompatibility but less mechanical strength compared to titanium. Despite this limitation, zirconium dioxide abutments have esthetic advantages, and so are regarded as the material of choice in the esthetic zone. However, clinicians should note that fracture of zirconium dioxide abutments can be problematic to manage as it is difficult to remove the zirconium dioxide material inside the implant connection. Furthermore, should a zirconium dioxide abutment become loose and move inside the implant, this movement can damage the implant connection interface as zirconium dioxide is harder than titanium.

The abutment materials have different clinical indications. Titanium is used for all the clinical indications listed here and therefore has maximum clinical flexibility. Zirconium dioxide is used for prefabricated or customized CAD/CAM abutments for single crowns, multi-unit FDPs, or full-arch reconstructions. Gold is used for customized abutments for single crowns, multi-unit FDPs, and full arches. PMMA and PEEK are used for fixed implant-supported provisional prostheses.

According to clinical studies and systematic reviews of studies with observation periods up to 5 years, ceramic abutments exhibit high survival and low complication rates similar to those of metal abutments. Clinical studies with observation time up to 11 years have shown excellent long-term outcomes in the anterior and premolar regions. A randomized clinical trial with a follow-up time of 5 years presented no statistically or clinically significant differences between the 5-year survival and technical and biological complication rates of zirconium dioxide and titanium abutments.

When comparing different abutment materials histologically, an in vivo histological study demonstrated that there are no visible differences in soft tissue health of the peri-implant mucosa adjacent to zirconium dioxide and titanium abutment surfaces. Another study showed that the soft tissue around zirconium dioxide heals faster than when in contact to titanium. In a systematic review the evidence of zirconium dioxide abutments was evaluated from animal and human histological studies. It was concluded that zirconium dioxide is as suitable an abutment material as titanium. Regarding plaque accumulation, zirconium dioxide appears to have a lower tendency for surface-bound bacterial plaque in early stages, which is advantageous. In a histological study on dogs from Welander and coworkers, stable soft tissue dimensions were seen with zirconium dioxide and titanium abutments, while, in contrast, an apical shift of the barrier epithelium and marginal bone was found around gold alloy.

Implant Abutment Materials, Key Learning Points: Different materials are available for implant abutments. Titanium is the all-around abutment material of choice because of its excellent biocompatibility, mechanical strength, and corrosion resistance. Zirconium dioxide also offers excellent biocompatibility together with added esthetic benefits. Caution is recommended in the clinical use of ceramic abutments in molar sites as their behavior in these sites has not been sufficiently evaluated.

Abutments have different clinical indications based on their design, type, and material. With numerous abutment options it can be bewildering to approach their selection from this angle. It is both simpler and more logical to approach their selection based on the prosthodontic indication and clinical situation they need to serve. In the following, recommendations for abutment selection will be presented on this prosthodontically driven basis.

Here is a prosthodontically driven decision process for implant abutment selection. This decision process can be used in prosthodontic planning prior to implant placement. The first step is to define the type of prosthesis. Different considerations will apply to single-unit, multi-unit and full-arch one-piece prostheses. Next you need to decide on the method of retention - should the prosthesis be cement retained or screw retained? Cement retention may simplify the procedure and facilitate passive fit whereas screw retention could allow prosthesis retrieval. This is followed by selecting the type of implant connection - single-units need an engaged connection for anti-rotation. For multi-unit and full-arch one-piece prostheses the choice between engaged and non-engaged connections depends on the method of retention of the prosthesis. Engaged is required for cemented, where abutments are a separate component whereas non-engaged is required for screw-retained. The fourth step is to determine the extent of flexibility required by the prosthodontic platform. Can this be achieved by the range of variation offered by prefabricated, standard abutments or does it require a customized abutment? The final step is to select type of abutment material. This will require a decision based on clinical factors such as esthetic and functional demands depending on prosthesis type, location and need for strength. The abutment selection should be confirmed after implant placement.

Here is an example of the decision process for implant abutment selection for a posterior single-unit prosthesis. The patient is a bruxist so screw retention is selected for ease of retrieval in case of chipping of the prosthesis. An engaged connection is chosen for precision fit and anti-rotation for a single-unit prosthesis. There is no particular need for flexibility of the prosthodontic platform. This is a one piece implant with an inbuilt shoulder at mucosal level and no need for correction of axis angulation. A prefabricated standard abutment is selected. Titanium is chosen as abutment material as there are no esthetic concerns and strength is needed for a posterior prosthesis in a known bruxist.

Here is an example of the decision process for abutment selection for two anterior implants that will be restored as separate, single-unit prostheses. Screw retention is selected to avoid issues with cement retrieval. An engaged connection is chosen for precision fit and anti-rotation for these separate single-unit prostheses. There is maximum need for flexibility of the prosthodontic platform to utilize the developed emergence profile and create an individual level of prosthesis margin. This requires a customized abutment. Zirconium dioxide is chosen as abutment material to improve esthetics in the presence of a medium periodontal phenotype and high lip line.

Abutment Selection for Fixed Dental Prostheses, Module Summary: Abutments provide the connection between fixed dental prosthesis and implant. Differences in abutment designs all have the common aim of providing prosthodontic solutions and flexibility for any given clinical situation. Standard abutments simplify the technical procedure and are time efficient. Customized abutments offer an individualized design to maximize prosthodontic flexibility. Zirconium dioxide as an abutment material is as suitable as titanium in the esthetic zone; however, caution is recommended for posterior sites. In posterior sites abutments made of titanium or gold are indicated. Abutment selection is made easier by following a systematic process based on prosthodontically driven planning.