An implant crown is the final prosthetic tooth secured onto a dental implant post. Cementing an implant crown is a highly specific, multi-step technical process due to the biological differences between an implant and a natural tooth root. A successful outcome requires meticulous attention to the abutment surface, the selection of the luting agent, and the complete removal of any excess material.
Understanding Cement-Retained Versus Screw-Retained Crowns
Not all implant restorations require cementation, as the final crown can be secured using one of two primary methods. A cement-retained crown involves cementing the prosthetic tooth onto an intermediary component called an abutment, which is itself screwed into the implant fixture. This design is favored for its superior aesthetics because it lacks any visible access hole.
A screw-retained crown attaches directly to the implant fixture, tightened through a small access hole on the biting surface. The choice between methods depends on the implant angulation, available space, and aesthetic demands. While screw-retained crowns offer easy retrievability for maintenance, cement-retained crowns are chosen for the front of the mouth where an access hole would compromise appearance.
Cement-retained crowns provide a more natural, seamless look, making them the preferred option when aesthetics are the priority. However, the use of cement introduces a unique risk. This risk necessitates a specialized procedure focused on meticulous cement removal.
Abutment Preparation and Isolation
The abutment, which receives the crown, must be thoroughly cleaned and prepared immediately before cement application. This preparation ensures the cement forms a secure, long-lasting bond with the surface material, often titanium or zirconia. The abutment is meticulously cleaned to remove residual debris, saliva, or provisional cement from the trial seating process.
Specialized cleaning agents, often alcohol-based or chlorhexidine solutions, are used to disinfect the abutment surface and promote a pristine bonding environment. A dry field is then achieved through isolation, typically using cotton rolls, gauze, or a rubber dam, to prevent contamination from saliva or blood. Achieving this dry, uncontaminated surface is a prerequisite for reliable cement adhesion.
A trial seating of the final crown is performed before mixing the cement to verify the fit, shade, and contact points. This step confirms the fit of the crown margin to the abutment margin, ensuring no large gaps exist that could lead to excessive cement extrusion. Some techniques involve protecting the sub-gingival portion of the abutment with a thin layer of material, such as PTFE tape, to reduce cement flow below the gum line during seating.
Selection and Application of Dental Cements
Choosing the correct luting agent is a deliberate decision, with options falling into two main categories: temporary and permanent cements. Temporary cements, often zinc oxide-based and formulated without eugenol, are selected when the clinician anticipates the need to easily remove the crown for future repairs or inspection. These provisional cements provide retention while remaining relatively weak, facilitating non-destructive retrieval.
Permanent cements, such as resin-modified glass ionomer or resin-based materials, are used when maximum retention and a definitive bond are desired. Resin cements offer superior strength, but their strong adhesion makes the crown difficult to remove without cutting it off. The cement is mixed according to the manufacturer’s instructions and applied carefully to the inner surface of the crown.
A precise amount of cement must be used to minimize the excess material extruded from the crown margins upon seating. The crown is then firmly seated onto the abutment with controlled pressure, allowing the excess cement to flow out evenly. Controlled seating speed and force are important, as rapid seating or excessive cement increases the amount that spreads into the surrounding gum tissue.
Post-Seating Procedures and Cement Removal
The most consequential step is the meticulous removal of all extruded cement. Excess cement must be completely cleared from the peri-implant sulcus, the small pocket of gum tissue surrounding the abutment. This area is biologically distinct from the gum around a natural tooth and is highly sensitive to foreign material.
Residual cement left below the gum line is a well-documented cause of peri-implantitis, leading to inflammation, bone loss, and potential implant failure. Specialized instruments, such as implant scalers or dental floss, are used to scrape and pull the setting cement from the sulcus area. This cleanup must be performed with great care to ensure no cement fragments are left behind, as they act as a chronic irritant and harbor bacteria.
The final, non-negotiable step is radiographic verification using an X-ray to confirm that no cement remains sub-gingivally. Even if the area appears visually clean, a radiograph taken at the appropriate angle detects radio-opaque cement remnants pushed deep into the tissue. This verification is a final safeguard against the long-term biological complications associated with retained cement.