A dental crown is a custom-made cap placed over a damaged or weakened tooth, restoring its shape, size, strength, and appearance. When decay develops beneath this covering, the question of whether a dentist can drill through the crown to remove the cavity is common. Yes, this procedure is often performed, usually reserved for smaller areas of decay or for accessing the pulp chamber for a root canal. The feasibility depends heavily on the crown’s material, the decay location, and the restoration’s integrity.
Why Cavities Form Around Crowns
A crown, made of synthetic material like porcelain, ceramic, or metal, cannot decay. The vulnerability lies in the natural tooth structure underneath, which is still susceptible to bacteria that cause dental caries.
Decay most commonly occurs at the crown margin, the junction where the edge of the crown meets the tooth structure near the gumline. A tight seal at this margin is essential to prevent bacteria and food debris from entering. If the seal is compromised, decay can begin.
Contributing factors include receding gums, which expose the unprotected tooth root surface. Microleakage can also occur if the dental cement holding the crown dissolves over time. Poor oral hygiene allows plaque to accumulate, leading to recurrent decay.
The Process of Drilling Through a Crown
The decision to drill through a crown preserves the existing restoration and avoids the more invasive process of crown removal. The dentist identifies the precise location of the underlying decay using dental X-rays and visual inspection. The area is numbed with a local anesthetic to ensure patient comfort.
Specialized rotary instruments, known as dental burs, penetrate the crown material. This requires a controlled approach, especially with brittle materials like porcelain or ceramic, which can fracture if drilled too aggressively. Metal crowns require specific carbide or diamond burs designed to cut through the hard alloy layer.
Once penetrated, the dentist accesses the underlying tooth structure. They meticulously remove the decayed dentin, often relying on tactile feedback since direct visibility beneath the crown is limited. The goal is to fully eliminate the infected material without compromising the remaining healthy tooth structure before sealing the access hole.
Sealing the Access Point After Repair
After the underlying decay is removed, the opening in the crown must be sealed to prevent future bacterial contamination. The material chosen is usually composite resin, a tooth-colored filling material. If the opening is in a non-visible area, an amalgam filling may be used for durability.
For ceramic crowns, the internal walls of the access hole are treated with special chemicals, such as hydrofluoric acid and a silane coupling agent. This prepares the surface for optimal bonding with the composite resin. This multi-step process creates a strong, durable seal between the filling material and the crown’s synthetic surface.
The repaired crown remains functional, but its structural integrity is slightly reduced. If the repair is on the visible surface of an all-ceramic crown, the filled area may be detectable, leading to a minor aesthetic compromise.
Situations Requiring Complete Crown Replacement
Drilling through a crown is a viable option for localized decay, but certain conditions mandate complete removal and replacement of the entire restoration.
If the recurrent decay is too extensive, having spread significantly under the crown, the remaining tooth structure may be severely compromised. In this case, simply filling the decay would not provide a long-term, structurally sound solution.
Crown replacement is also necessary if the existing crown is ill-fitting, allowing bacteria to continually enter at the margin. Replacement is unavoidable if the crown is severely cracked or fractured during the drilling attempt, as its protective function is lost.
Furthermore, certain high-strength ceramic materials, like some forms of zirconia, are difficult to bond to reliably after access, making a long-term seal questionable. Replacing the entire crown, while more invasive, offers the opportunity to remove all decay and secure a fresh, precisely fitted restoration. A new crown ensures an ideal margin seal and optimal strength, providing a more predictable and durable long-term outcome.