Dental implants retain fixed and removable restorations, including single crowns, fixed bridgework, and implant-supported dentures. The technology for dental implants is well-established, and success rates are extremely high. Many dental practices have already embraced implant dentistry, and it is a significant source of revenue. As patient awareness increases, demand for the treatment will only increase.
Experienced clinicians know that advanced planning and precise implant placement is vital. An accurate implant impression is fundamental to giving the patient a successful prosthesis that closely resembles the appearance and function of natural teeth. The primary objective when taking an implant impression is to accurately record the coronal position of the implant fixture head in relation to other structures in the mouth. Once the prosthesis is fabricated and seated in the mouth, the clinician must fit it correctly to achieve a passive fit and long-term success.
Identifying the Implant Components
The first step of the procedure is to identify the implant components, because this will dictate the impression components used. Each implant system requires its own set of impression components, which are designed to fit precisely onto the fixture head of the implant. Although this step might sound easy, it’s not always straightforward, and it might be necessary to refer to the patient’s notes. Once the implant system has been identified, the components and techniques used when taking an impression are similar.
Selecting an Impression Tray
Impression trays can be stock trays or custom-made. Usually custom-made trays are a better choice because they tend to be more rigid and are fabricated to ensure that an optimal thickness of impression material is used. Trays used for implant prosthodontics are categorized as open or closed. The difference is that, unlike a closed tray, an open tray allows the clinician direct access to the implant fixture head while the tray is seated in the mouth.
Fabricating a Custom Impression Tray
A primary impression is required to fabricate a custom impression tray. The primary model will provide a good idea as to the angulation and position of the dental implants. It tells the technician which impression material to use so that an appropriate spacer can be laid down. A custom tray is designed to take an impression at abutment level, at fixture head level, or at both in the same impression.
Choosing Impression Materials
Your chosen impression material should be accurate, easy to mix, and rapid to set. After removal from the mouth, it must remain dimensionally stable. The impression material provides an accurate representation of the tissues and should have good flow and high tear strength, like vinyl poly siloxane, or polyether materials. Impression materials with desirable properties are hydrophilic and have good wettability.
Selecting the Correct Screwdriver
An implant screwdriver is used to screw and unscrew implant components onto the fixture head and is a critical piece of equipment. Screwdriver heads vary in shape according to the implant system and can be designed to fit into a torque device.
Healing Caps or Abutments
Usually, the fixture head is level with the alveolar bone crest, and a healing abutment or cap is screwed onto the head at the time of implant placement or during a second surgical procedure to uncover the implant. The height, profile, and width of healing caps or abutments vary, and the surgeon will select an appropriate size to shape the peri-implant tissues during healing. Your dental lab will need to know the height of the healing abutment when making a custom-tray so that they can estimate the thickness of the soft tissues and provide adequate space for the implant components.
An impression coping fits onto the fixture head or the implant abutment while the impression is taken. When a closed tray is used, the impression coping is retained in the mouth when the impression is removed. When used with an open tray, the impression coping remains in the impression when it is removed. Once the impression is cast, the impression copings will transfer the position of the implant abutment or fixture head to the working model.
Abutments may be stock or custom-made to accommodate the patient’s esthetic demands. Custom-made abutments are frequently fabricated using CADCAM technology and are designed to hide the junction between the abutment and the crown. Usually titanium, sometimes zirconia.
Step-By-Step Closed Tray Impression Technique
- Expose the fixture head by removing the healing abutment and select an appropriate closed tray impression coping to fit onto the fixture head.
- If you feel unsure about its positioning, check that the coping is seated with a radiograph.
- Try in the stock or custom tray. It must cover the entire arch. Ensure that there is sufficient vertical space for the impression coping and the impression material.
- Inject light-bodied, low-viscosity impression material around the implant and the surrounding soft tissue, and use high-viscosity or heavy-bodied impression material to fill the rest of the tray. Don’t use too much light-bodied impression material, because it lacks the rigidity required for a good implant impression.
- Once the material has set, carefully remove the impression, leaving the coping in the mouth.
- Remove the impression coping from the mouth and reposition it in the impression, checking that it relocates positively. There will usually be an audible or tactile “click”.
- Replace the healing abutment.
Step-by-Step Open Tray Impression Technique
A custom-tray is fabricated with a section or window cut through over the implant.
- Remove the healing abutment, and fit an impression coping. If necessary, splint multiple copings together in the mouth to provide greater stability.
- Try in the custom-tray to check that the impression coping is level with the window. The positioning of the impression copings facilitates easy removal while still ensuring that the impression material adequately supports the copings.
- Seal the window with wax. You should be able to feel the tips of the impression copings through the wax.
- Take the impression using the appropriate impression material and allow it to set.
- Once the impression copings are set, access and unscrew them through the window. Remove the impression from the mouth with the impression copings in place.
- Finally, replace the healing abutments.
Once you’ve taken an implant impression, inspect it to ensure that all teeth are recorded for articulation so that the technician can accurately match the tooth contours. The impression coping must be firmly seated in the impression and analogs. Implant replicas are attached to the coping before casting.
Please be reminded that should you wish to discuss a case in more detail, our experienced technical team is here to assist you.