A dental crown, often referred to as a cap, is a custom-made restoration placed over a damaged or weakened tooth to restore its shape, size, strength, and appearance. This protective cover is bonded to the tooth structure, improving functionality and providing long-term protection. While crowns are durable, they are not permanent and occasionally need removal or replacement for various clinical reasons. Understanding the process helps patients feel informed about the procedure.
Clinical Necessity for Removal
The decision to remove an existing crown is based on assessing the restoration’s integrity and the health of the underlying tooth. The most frequent reason is recurrent decay (dental caries) forming underneath the crown margin, often due to an imperfect seal. This requires crown removal to access and eliminate the infected tooth structure.
Structural issues also necessitate removal, such as a fractured crown, a chipped porcelain layer, or a crack in the supporting tooth. A crown may also be removed if it has a poor fit, which can lead to chronic gum irritation or bite problems. Furthermore, removal may be needed to gain access for a necessary procedure, such as a root canal retreatment or to address an underlying infection or inflammation.
Non-Destructive Techniques
When a crown is new, temporarily cemented, or the underlying tooth structure is fragile, a dentist may first attempt a non-destructive removal technique for potential reuse. These methods aim to break the cement seal without damaging the crown or the underlying tooth. One approach is to use specialized instruments, such as crown removal pliers or a metal lever, which apply controlled leverage or traction.
Another technique involves applying ultrasonic vibration to the crown, transmitting energy to the luting cement. The mechanical vibration causes a breakdown in the cement layer, weakening the bond. These conservative techniques are most successful with crowns secured by weaker, temporary cements or those that have already begun to loosen.
Sacrificial Removal Techniques
For crowns that are permanently and strongly bonded, non-destructive methods are often unsuccessful, requiring sacrificial techniques where the crown is intentionally damaged for removal. The most common and reliable method is crown sectioning, which involves using a high-speed dental drill and a specialized bur to cut a groove completely through the crown material. This cut is typically made from the biting surface down to the gumline on one side, which breaks the cement seal and relieves the internal retention.
The choice of bur is specific to the crown material to ensure efficient cutting and minimize heat generation. For a porcelain-fused-to-metal crown, a diamond bur cuts the porcelain, followed by a tungsten carbide bur for the metal layer underneath. Solid ceramic materials, such as zirconia, require aggressive, specialized diamond burs due to their extreme hardness. Once the crown is sectioned, a specialized instrument, like an elevator, is placed into the cut groove and gently rotated to pry the halves apart, allowing the crown to be lifted off the tooth. Local anesthesia is administered beforehand to ensure patient comfort.
Post-Removal Procedures
Once the crown is successfully removed, the focus shifts to the underlying tooth structure and preparing for a new restoration. The dentist thoroughly examines the exposed tooth, also known as the core, for any signs of decay, cracks, or structural defects. Any remaining old cement is meticulously cleaned from the tooth surface to ensure a clean foundation.
If decay or a fracture is found, it must be treated, often involving the removal of the affected tooth structure and rebuilding the core with filling material. After the underlying issues are addressed, a temporary crown is immediately placed over the prepared tooth. This temporary restoration protects the sensitive tooth core from temperature changes, prevents the surrounding teeth from shifting, and maintains the space until the new, permanent crown is fabricated and ready for placement.