A cement-retained implant crown is a prosthetic restoration permanently fixed onto an implant abutment using specialized dental cement. This configuration offers superior esthetics by eliminating the visible screw access hole often seen in other restorations. Cement-retained crowns also allow the dentist to compensate for implants placed at a less-than-ideal angle, simplifying restoration. Although seemingly permanent, the crown sometimes requires removal for maintenance or repair. Removal methods are carefully chosen to preserve the underlying implant structure while addressing the complication.
Clinical Necessity for Removal
The need to remove a cemented crown arises from mechanical or biological complications threatening the implant’s health and stability. A frequent mechanical reason is the loosening or fracture of the abutment screw, which connects the abutment and crown complex to the implant body. Although tightened to a specific force, the screw can lose torque over time, causing the crown to feel loose. If ignored, this can damage the implant’s internal connection. Dentists must remove the crown to access, retighten, or replace this screw.
A serious biological reason for removal is peri-implantitis, which is infection and inflammation of the tissue and bone surrounding the implant. This condition is often linked to residual cement left below the gum line during initial crown placement. The excess cement acts as a foreign body, allowing bacteria to accumulate and cause chronic inflammation. Untreated inflammation can lead to progressive bone loss and implant failure. Removing the crown provides necessary access to thoroughly clean the abutment surface and infected tissue.
Structural damage, such as a major fracture in the porcelain or ceramic layer, also necessitates removal. A significant fracture compromises the crown’s integrity and function, requiring replacement. If the cement seal around the crown margin washes out, it can lead to marginal leakage. This leakage allows oral fluids and bacteria to seep underneath the crown. This can cause decay on the abutment or other complications, making crown retrieval necessary for assessment and repair.
Pre-Procedure Diagnostic Assessment
Before attempting removal, the dental professional conducts a thorough diagnostic assessment to formulate a safe strategy. A key initial step is obtaining a high-quality periapical radiograph or a Cone Beam Computed Tomography (CBCT) scan. These images determine the exact location and angulation of the abutment screw access channel, which is hidden beneath the crown material.
The assessment identifies the specific materials used, including the crown material and the type of cement. Materials like porcelain, zirconia, or metal require specialized burs and techniques for cutting without causing damage. The type of cement used (temporary or strong resin-based) indicates the expected bond strength and necessary removal force.
Knowing the implant brand and type is important to ensure the correct driver is available to remove the abutment screw. The dentist estimates the screw access hole’s position using external landmarks and digital imaging software for precision. The patient is informed that while non-destructive removal is the goal, a strong cement bond may require the crown to be sectioned or drilled through, potentially requiring a new crown.
Techniques for Crown Removal
Non-Destructive Methods
The approach prioritizes the least destructive method to potentially preserve the restoration. The first technique uses specialized mechanical crown removers or rubber-coated pliers to grip the crown firmly. The dentist applies controlled, quick pressure in a bucco-lingual (cheek-to-tongue) direction, followed by rotational movement, attempting to shear the cement bond. This method is most effective when a weaker, temporary cement was used.
Another non-destructive approach utilizes ultrasonic energy applied with a specialized scaler tip placed along the crown margin. The high-frequency micro-vibrations disrupt the bond between the cement and the abutment surface. This technique is applied intermittently, allowing the energy to fatigue the adhesive and loosen the crown without excessive force. Some specialized systems use leverage, applying force to a designated slot in the crown’s substructure to predictably break the cement seal.
Destructive Methods
When non-destructive methods fail, or if the goal is accessing a loose abutment screw, creating an access channel is necessary. This involves carefully drilling a small, precise hole through the occlusal (biting) or lingual (tongue side) surface directly over the estimated screw location. Specialized diamond burs cut through ceramic or porcelain, followed by metal-cutting burs if a metal substructure is present. Water coolant is used throughout to prevent overheating.
The goal of the access channel is to create an opening down to the head of the screw, converting the cemented crown into a retrievable screw-retained restoration. If the entire crown must be removed, the dentist may section it completely by cutting a slit from the occlusal surface down to the margin. This cut relieves the internal stress of the cement bond, allowing the crown to be pried off in pieces. Excessive force is avoided to prevent stripping the implant body’s internal threads, which could cause irreversible damage.
Immediate Post-Removal Steps
Once the crown is removed, attention shifts to the underlying abutment and implant. The abutment surface must be meticulously cleaned to remove all traces of residual cement, especially if cement retention caused the complication. Residual cement can interfere with the fit of a new restoration or irritate the peri-implant tissues.
The integrity of the abutment screw and the implant’s internal connection are inspected for wear, stripping, or deformation. If the screw was loose, the dentist replaces it with a new one. A calibrated torque wrench is used to tighten it to the manufacturer’s specified force, typically 20 to 35 Newton centimeters (Ncm). This specific torque ensures the screw is securely clamped and prevents future loosening.
If removal was due to peri-implantitis, the dentist performs thorough debridement of the inflamed tissue and exposed implant surface to eliminate infection. Afterward, a new crown is fabricated, or the original crown is prepared for re-use if preserved via the access channel method. The access channel is filled with inert material, such as Teflon tape, and sealed with composite resin, completing the conversion to a retrievable restoration. A temporary restoration may be placed to protect the site and maintain aesthetics while the definitive crown is manufactured.