A dental implant system replaces a missing tooth using several components. The system begins with the implant fixture, a titanium post surgically placed into the jawbone. The abutment serves as a connector piece, and the final component is the prosthesis, such as a crown or bridge, which functions like a natural tooth. The location where the prosthesis connects to the underlying parts defines two distinct clinical strategies.
The Implant-Level Approach
The implant-level approach involves attaching the final crown or bridge directly to the implant fixture within the jawbone. This method places the junction between the restoration and the implant at or below the gumline. This design is almost always screw-retained, meaning a small screw passes through the crown to secure it to the implant fixture. The use of a screw eliminates the need for dental cement and allows for easier retrievability.
This technique is often selected when the vertical space in the mouth is limited, as it does not require the additional height of a separate abutment. However, the procedures can be more technically complex, as manipulating components below the gumline requires precise handling to avoid traumatizing the surrounding soft tissues.
The Abutment-Level Approach
The abutment-level approach uses a separate component, the abutment, which is first secured to the implant fixture. The final crown is then attached to this abutment, elevating the connection point to a position at or slightly above the gumline. This approach is most frequently paired with cement-retained crowns, where the restoration is bonded onto the abutment.
This method can simplify clinical and laboratory procedures, as taking an impression of an abutment level with the gums is less invasive. A functional advantage is its ability to correct for implants placed at non-ideal angles through the use of a custom-angled abutment.
Key Deciding Factors for Dentists
Implant Position and Angulation
The depth and angle of the implant fixture in the jawbone are significant in determining the approach. When an implant is placed deep below the gumline, an implant-level restoration is often preferred to avoid creating an overly long abutment, which could compromise stability. Conversely, the abutment-level approach offers a solution for implants placed at an angle due to anatomical constraints. A custom-fabricated abutment can correct the alignment, allowing the final crown to be placed in an ideal position for aesthetics and function.
Cement Control and Periodontal Health
Managing dental cement is a consideration for gum health. With abutment-level, cement-retained restorations, there is a risk of excess cement being extruded below the gumline during seating. This residual cement is a primary cause of peri-implant inflammation and can lead to bone loss, a condition known as peri-implantitis. Placing the crown margin at or above the gumline with an abutment makes it easier for the dentist to see and remove any excess cement.
The implant-level, screw-retained approach avoids this issue. Since no cement is used, the risk of cement-induced peri-implantitis is eliminated, which is a long-term health advantage.
Aesthetics
The final appearance of the restoration, especially for front teeth, is a factor. Abutment-level restorations can provide excellent aesthetic outcomes, particularly when tooth-colored zirconia abutments are used. These abutments prevent the dark color of the underlying metal implant from showing through thin gum tissue and support the surrounding gum tissue profile.
Implant-level, screw-retained crowns present an aesthetic challenge due to the screw-access hole on the biting or tongue-facing surface of the crown. This opening must be sealed with a composite filling material after the crown is secured. While this material can be matched to the shade of the crown, its visibility can be a concern for some patients.
Retrievability and Maintenance
The ability to easily remove and reattach the crown is an advantage of the implant-level, screw-retained approach. This retrievability allows for straightforward maintenance, such as professional cleaning, repair of the porcelain, or tightening a loose screw. The process is non-destructive to the crown.
Removing a crown that has been permanently cemented onto an abutment is more difficult. The process often requires cutting the crown off, which destroys it and necessitates the fabrication of a new one, making future maintenance more costly.