The process of replacing a missing tooth with an implant involves three main parts: the titanium post placed in the jawbone, the artificial tooth called the crown, and a connecting piece that links the two. The final stage of this restoration is securing the crown to the implant system, which transforms the internal hardware into a fully functional, visible tooth. This attachment phase is executed using one of two primary mechanical methods, each offering distinct advantages based on the patient’s individual clinical needs and aesthetic requirements.
The Essential Connecting Piece
The crown is not typically attached directly to the titanium implant post anchored in the bone, but rather to an intermediate component known as the abutment. The abutment functions as a connector piece that screws directly into the implant body, extending the artificial root above the gumline. This connector is designed to mimic the structure of a prepared natural tooth, providing a stable platform for the final crown.
Abutments are fabricated from materials like titanium, gold alloy, or zirconia and can be either pre-manufactured or custom-milled for a precise fit. The shape of the abutment is important because it helps form the surrounding gum tissue, ensuring a natural contour where the crown meets the soft tissue. This prepared base ensures the crown receives stable support for chewing and biting forces.
Screw-Retained Attachment
In the screw-retained method, the crown and the abutment are often fabricated as a single unit or permanently joined before placement. This entire structure is seated over the implant and secured by a small prosthetic screw. The screw passes through the biting surface of the crown and threads directly into the implant post, providing a direct mechanical lock.
The screw pathway creates a narrow access hole visible on the top or back surface of the crown. Once the screw is tightened, this access channel is sealed and masked using a color-matched composite resin material. A primary advantage of this technique is its retrievability, allowing a dentist to easily remove the crown for maintenance or repair without damaging the restoration.
A disadvantage of screw retention is the potential aesthetic compromise caused by the access hole, which may be noticeable on front teeth. The implant positioning must be ideal to ensure the screw channel emerges in a discreet location. However, the elimination of dental cement makes this method popular, as it avoids complications associated with residual cement beneath the gumline.
Cement-Retained Attachment
The cement-retained method closely mimics placing a traditional crown on a prepared natural tooth. The abutment is first secured to the implant using a separate abutment screw. The crown is then permanently bonded onto the abutment using specialized dental cement, which provides retention and creates a solid connection.
This approach offers a superior aesthetic result because there is no screw access hole on the crown surface, leading to a smooth, uninterrupted biting surface. Cement retention is frequently chosen for implants in the highly visible front area of the mouth. The procedure also provides flexibility, as the cement layer can help compensate for slight angles in the implant placement.
The primary risk is the potential for excess cement to remain under the gumline, which can be difficult to remove completely. This excess cement may lead to tissue inflammation or infection around the implant. If the crown requires future repair, the cemented connection makes the restoration difficult to retrieve non-destructively, often requiring the crown to be sectioned and destroyed.
Why Dentists Choose Different Methods
The selection between a screw-retained or cement-retained crown is based on an assessment of several clinical factors. For front teeth, where appearance is a high priority, a dentist may favor the seamless look of a cement-retained crown. Conversely, if the implant is located in the back of the mouth, the ease of maintenance and predictable retrievability of a screw-retained crown often makes it the preferred choice.
The amount of vertical space between the implant and the opposing jaw also plays a role, as does the angle of the implant post. Cement-retained crowns can sometimes accommodate implants placed at a less-than-ideal angle more easily than traditional screw-retained designs. Modern innovations, such as angulated screw channel technology, have expanded the use of screw retention by allowing the access hole to be strategically positioned away from the biting surface.
Ultimately, the goal is to balance aesthetic outcomes with long-term serviceability and biological health of the surrounding tissue. Many clinicians prefer screw retention where possible to avoid the risk of cement-related complications. The final choice reflects a tailored approach to ensure the longevity and function of the dental restoration.