Implant impressions are important for the fabrication of dental prostheses. The aim of implant impressions is accurate transfer of the intra-oral implant situation to the dental laboratory. It is possible to record the implant situation with conventional analog impression techniques, or using digital technologies. All implant impression techniques employ a variation of the pick-up or transfer impression technique sometimes used in conventional, tooth-borne prosthodontics.

In the case of implant impressions, a precision-made impression component is used to register the position, alignment, and rotational orientation of the implant. The impression, whether it follows a conventional (that is, analog) or digital workflow, then records this information in relation to the surrounding hard and soft tissues. This module will deal with conventional impression techniques and all of the parameters involved.

After completing this ITI Academy Module, you should be able to: define conventional implant impression, list the essential requirements of a conventional implant impression, define conventional implant impression components and techniques, outline the workflow of a conventional implant impression, describe the specific impression technique for transfer of custom soft tissue emergence profile of implant prostheses.

A conventional dental impression can be defined as a physical registration of the hard and soft tissues such as teeth, gingival tissues, and alveolar contours, from which a dental cast can be constructed. A conventional implant impression also includes the physical registration of the position, alignment, and rotational orientation of individual implants together with their relationship to the surrounding hard and soft tissues. Most implant systems have internal indexing features such as grooves or slots within the shoulder of the implant to allow their rotational orientation to be recorded.

A conventional implant impression needs to be as accurate a registration as possible. Construction of implant-supported fixed dental prostheses is an exacting procedure due to the rigid fixation of implants and the often complex and precise nature of implant components and their insertion. It is therefore essential that the physical registration is as precise as possible to ensure that the clinical situation is replicated correctly in the dental laboratory. In the right image, part of the cast around the implants is made from an elastic silicone rubber material. This cast is referred to as an "anatomic soft tissue cast" because it reproduces the soft tissues around the implant in an elastic material. The elastic material simulates the natural compressibility of the soft tissues and can be removed from the cast to allow direct access to the implant analogs.

Definition and Purpose of Conventional Implant Impressions, Key Learning Points: A conventional dental impression is a physical registration of hard and soft tissue structures from which a dental cast can be constructed. A conventional implant impression additionally includes physical registration of implant position, implant indexing features, and peri-implant mucosa. Due to the rigid fixation of implants and often complex and precise fit and insertion of implant components, conventional implant impressions need to be as accurate as possible.

For the conventional implant impression to be as accurate as possible it must satisfy a number of essential requirements. These are: use of a rigid impression tray that securely confines and carries the impression material, use of a rigid and dimensionally stable impression material with good tear resistance, and use of implant-specific, prefabricated impression components. These requirements will now be covered individually in more detail in the following slides.

The impression tray needs to be rigid to prevent distortion and dislodgement of impression material and implant components. It needs to have adequate extension to ensure it includes all areas of interest. Next, it needs to carry and confine the impression material to limit material flow while the material sets. Finally, to avoid distortion or dislodgement there must be no contact between the impression tray and the structures or components to be recorded.

There are generally two options for choice of impression trays. The first option is a prefabricated tray, also referred to as a stock tray. Two examples can be seen here. For adequate rigidity it is recommended that the stock trays be made of metal or rigid plastic. The second option is a custom-made impression tray, as seen in the images on the right. Custom trays can be fabricated from autopolymerizing methyl methacrylate or composite resin. Seating stops can be included in the custom tray in positions clear of any of the structures and components that are to be recorded. These stops will ensure optimal impression material thickness and clearance of impression components.

The literature supports use of both stock and custom made trays, but it is acknowledged that a custom impression tray is the best option for achieving an impression with an optimal thickness and confinement of impression material around the hard and soft structures and implant components to be recorded.

The prerequisites for the selection of acceptable impression material are as follows: The material should be dimensionally accurate. It should also be rigid and have good tear resistance, and it should be dimensionally stable over time. The adhesion strength of an impression material to a custom tray had an important role in preventing distortion and/or detachment when the impression tray is removed from the mouth. The performance of polyether and polyvinyl siloxane or PVS material has been proven in all these respects over time.

Implant impression components also need to satisfy essential requirements. They need to be accurate with a rigid construction and a precise and secure fit to the implant. To achieve this, the impression components need to be implant-type specific, and all implant systems therefore manufacture specific impression components for all their implant types.

Next, the implant impression component must have adequate retentive features to avoid dislodgement. This applies both to a secure fit to the implant during the impression-taking procedure, and a secure fit and retention within the impression material upon and after removal. Finally, it is important that original impression components are used to ensure they possess the accuracy of fit and tolerance designed by the manufacturer.

Essential Requirements, Key Learning Points: To ensure accuracy of the conventional implant impression the impression tray must be rigid with adequate extension and confinement of the impression material whilst not touching any of the structures or components being recorded. The impression material must be rigid and dimensionally stable over time with good tear resistance. The impression components must be accurate, implant specific and have adequate retentive features to avoid dislodgement during or after the impression taking.

Implant impression components can be divided into impression components and implant analogs. The impression components act as a precise transfer of position, alignment, and rotational orientation of the implant. Implant analogs are precise implant replicas and are used in the laboratory working cast.

As a general rule there are implant impression components for every implant type in an implant system. In addition there are often different types of impression components for the same implant type. This is to allow for choice in management to suit the prosthodontic plan and local requirements of the clinical situation. The differences in design, however, may also dictate differences in impression technique. The choices in management and differences in impression techniques will be covered in the following slides.

To facilitate choice in prosthodontic management, impression components are usually available for registration of implants at the implant level and at the abutment level. An impression at the implant level can be defined as recording of the implant with no secondary definitive prosthodontic components attached. Impression at implant level offers maximum prosthodontic flexibility for abutment confirmation on the working cast. It also allows construction of a custom abutment. By contrast, impression at the abutment level refers to an impression in which an abutment has been selected and fitted to the implant in the mouth, and the purpose of the impression is to record the position of the abutment. An impression taken at abutment level leads to a simpler process in which only the prosthesis is constructed on the cast.

Local clinical requirements also play a role in choosing between different types of impression components. It is always wise to check whether the impression component design and construction material is suitable for the specific clinical situation. Following are examples of factors to consider: The impression component sometimes needs to be modified to allow it to seat correctly. This could be due to proximity of an adjacent tooth, another implant, or other oral structure. The component must retain its accuracy despite the modification. It may be necessary to verify correct seating of the component via a radiograph. A radiopaque component is needed for this purpose. The systematic review by Papaspyridakos supports rigid splinting of multiple components for both full and partially edentulous arch cases. If this approach is chosen it is important to ascertain that the selected impression component design is suitable for splinting and that all the splinted components can be withdrawn together without distortion. The impression component in the example shown has a very precise internal connection design, which, if splinted to other components of implants with divergent axes, may prevent simultaneous removal. For multiple implants with significantly diverging implant axes, impression at abutment level may be the solution. The example on the right shows a shallow angled abutment designed to overcome issues of divergence and its corresponding impression component.

Generically, impression components are divided into two types, the direct, pick-up type and the indirect, transfer type. The two different types can dictate a significant difference in the conventional implant impression technique. Direct pick-up refers to the component being removed with the impression as a single unit. By contrast, indirect transfer components are used to record a negative likeness of the component and the component is not removed with the impression. Instead, the component (and attached analog) must then be repositioned into the impression to allow the final cast to be prepared.

A recent systematic review by Papaspyridakos and colleagues reported better accuracy of implant registration for fully edentulous situations with use of direct pick-up components than indirect transfer components. The review does not offer an explanation for this, but it could be due to inaccuracies introduced by reinsertion of the indirect transfer component.

As mentioned in the previous slide, the choice of generic impression component will dictate a difference in the impression technique. Most direct pick-up impression components are screw-retained. To allow a screw-retained component to be removed with the impression as a single unit, it must be unscrewed before the component and impression can be removed together as one. This requires access to undo the component screw through the top of the tray. This access is referred to as an open tray technique. An example of an open tray with access to a screw-retained direct pick-up component can be seen in the clinical image on the right. By contrast, the indirect transfer component is not removed with the impression. As there is no need for access through the top of the impression tray to the indirect transfer component the impressions are therefore referred to as a closed tray technique.

Implant analogs exist for every implant type in an implant system. If there are different impression components for an implant type, there will also be appropriate corresponding analogs. The examples shown here include two implant-level analogs for a standard-diameter implant on the left and a wider-diameter implant in the middle. The abutment-level analog on the right corresponds to an abutment-level impression component of the same standard-diameter implant as shown on the left.

The implant analog is inserted into the impression component in the conventional implant impression. The implant analog then becomes incorporated in the working cast when this is poured from the impression. The example in the middle shows an abutment-level analog in a working cast, whereas the example on the right shows an implant-level analog.

Implant Components and Impression Techniques, Key Learning Points: Implant impression components act as transfer of implant features. Implant analogs act as implant replicas in the laboratory working cast. Common to all implant systems are impression components and implant analogs to correspond to all implant types in a system. Implant-level impressions offer greater prosthodontic flexibility for selection of the abutment. Abutment-level impressions make for a simpler process and can overcome difficulties with significant implant axis divergence.

Other considerations in choice of impression component include suitability for modification, need for radiographic contrast, suitability for splinting and correction of implant axes divergence. Impression components are generically divided into direct pick-up and indirect transfer types. The published literature supports direct pick-up as leading to more accurate impressions. An open tray technique is needed to allow removal of screw-retained direct pick-up components. The closed tray technique can be used with indirect transfer components.

The impression workflow for a conventional implant impression can be divided into four stages. The first stage is planning. The second stage is preparation. The third stage is making the impression, and the fourth is to make the laboratory cast. The four stages will be described in detail in the following slides.

The first stage in the impression workflow is the planning of the impression. This starts with selection of the appropriate type of impression component. As established in the previous learning objective, this selection will be subject to the prosthodontic plan and assessment of the clinical situation. In turn, the type of impression component will determine whether an open or a closed impression tray technique is needed. Next is the decision whether to use a stock or custom tray for the impression and finally, which type of impression material will be used. In the clinical example used here to demonstrate the impression workflow, the prosthodontic plan is a 3-unit FDP supported by two implants. Direct pick-up impression components are selected for accuracy of the recording of the implant positions. The screw retained direct pick-up component shown requires an open tray technique. A custom tray of composite resin with seating stops is chosen together with polyether impression material. This completes the planning of the impression.

The preparation for the impression starts with blocking out. As the impression material should be rigid and tear resistant, it is important to identify and block out any interdental spaces and deep undercuts in the arch where the impression material could otherwise get locked in. Then, the healing cap or abutment is removed and the impression component placed. Ensure that the component is correctly seated and securely retained. For submucosal implant shoulders, a radiograph may be needed to confirm proper seating of the component. Next, try in the impression tray and check that it can seat as intended without touching or dislodging the impression component. For an open tray impression the access holes should allow clear access to the component guide screws, as seen here.

For making the impression the impression tray is filled with regular or heavy-body impression material, and light-body material is injected around the impression component. The tray is inserted in the mouth and seated carefully. For an open tray technique any excess material covering the access to the component guide screw should be removed. Support the tray during the setting and follow the manufacturer's instructions for duration of setting time. When the setting is complete, the impression is removed. For an open tray impression, the guide screw should be unscrewed and the repeated click of screw disengagement confirmed before attempting to remove impression.

Before the laboratory working cast is made it is essential to confirm that the impression component is correctly and securely retained in the impression. For an indirect transfer impression component, which is not removed with the impression, the component must also reinsert correctly back into position in the impression and then be secure. Next, an analog that corresponds to the impression component should be inserted to check that it can be fitted correctly to the component, without dislodging it. The impression can then be poured in the clinic or in the laboratory as an anatomic soft tissue cast.

Impression Workflow, Key Learning Points: The workflow for a conventional implant impression can be divided into four stages. The first stage is planning the impression by selecting impression components, impression technique, and type of tray. The second stage is to prepare for the impression by blocking spaces and undercuts, seating the component correctly, and checking that the impression tray fits without coming into conflict with the components. The third stage is to make the impression whilst supporting the tray and clearing access to the impression components if appropriate. The fourth stage is to make the laboratory working cast, having ensured that the analog is correctly fitted to the impression component.

Soft tissue emergence profile is the term used to describe the shape of the soft tissue in the transition zone from top of the implant to the mucosal margin. Soft contours in the esthetic zone are highly scalloped, and a provisional prosthesis is recommended to develop an optimal emergence profile that supports the interproximal tissues and mimics the gingival architecture of adjacent teeth. Custom emergence profiles are developed by provisional prostheses. A custom emergence profile can also be useful in posterior sites. An optimal emergence facilitates esthetics and peri-implant access for effective, daily removal of biofilm during home care.

A modification of the conventional implant impression technique is required when transfer of a soft tissue custom impression emergence profile is involved. An additional stage is introduced in the workflow to construct a custom impression component that replicates the custom emergence of the provisional prosthesis. This custom impression component is then used to take the conventional implant impression. The construction of a custom component will be covered in the following slides.

For the additional stage of constructing a custom impression component, the procedure is as follows: A provisional prosthesis is fabricated to shape the mucosal tissues, and the patient is instructed to return after 30 days for evaluation. If the soft tissues are satisfactory, the provisional prosthesis with abutment are removed from the mouth and attached to an analog. This assembly is placed into a fast-setting bite registration material, which is allowed to polymerize. The provisional prosthesis and abutment are then removed and an impression component is inserted in their place. There will be a void between the impression component and the contours of the emergence profile. This void is filled with a flowable composite.

The custom impression component is tried in the mouth. It is important to ensure that there is clearance between the custom features and the adjacent teeth. The impression can now be taken by reverting to the workflow previously described; the custom impression component will be picked up in the impression. When the impression is poured as an anatomic soft tissue model, the reproduction of the peri-implant tissues will have the same emergence as the provisional prosthesis.

Transfer of Soft Tissue Custom Emergence Profiles, Key Learning Points: Soft tissue emergence profile is the term used to describe the shape of soft tissue in the transition zone from top of the implant to the mucosal margin. Transfer of a custom soft tissue emergence profile to the laboratory working cast requires an additional step in the conventional implant impression workflow for construction of a custom impression component.

Conventional Implant Impressions for Fixed Dental Prostheses, Module Summary: The aim of the conventional implant impression is an accurate, physical registration of the implant position and its relationship to surrounding hard and soft tissue structures, from which a dental cast can be constructed. The essential requirements of a conventional implant impression include use of an adequate impression tray and material and implant-specific impression components. A selection of implant components and techniques are available to facilitate prosthodontic management and to address case-specific clinical requirements. The workflow of a conventional implant impression can be divided into four stages: planning the impression, preparation for the impression, making the impression, and construction of the laboratory cast. Transfer of a custom emergence profile introduces an additional stage for construction of a custom impression component.