A dental crown is a custom-made cap designed to cover and protect a damaged or weakened tooth, restoring its shape, size, and function. While crowns are built to be long-lasting, they are not permanent and eventually require replacement due to normal wear, underlying decay, or a compromised fit. The process of replacing a crown requires carefully removing the old restoration without causing harm to the natural tooth structure underneath. The dentist must first determine the reason for removal and then select a technique that is least invasive to safely break the cement seal holding the crown in place.
Assessing the Crown and Patient Preparation
The crown replacement procedure begins with a thorough diagnostic assessment of the existing crown and the underlying tooth. The dentist typically uses dental X-rays to evaluate the condition of the tooth root, the surrounding bone, and to check for hidden decay beneath the crown margins. A visual inspection identifies cracks, signs of cement washout, or an open margin where the crown meets the gum line, indicating the need for replacement.
Patient comfort is addressed early through the administration of a local anesthetic to numb the area. Isolation techniques, such as placing cotton rolls or a rubber dam, are employed to keep the tooth dry and protect the surrounding soft tissues from the instruments used during the procedure.
The initial assessment helps the dentist anticipate the level of retention and determine the most effective removal method. Factors like the type of cement originally used and the crown’s material—such as porcelain-fused-to-metal, all-ceramic, or zirconia—influence the choice between conservative removal or the destructive cutting method.
Non-Destructive Techniques for Removal
If the underlying tooth structure appears healthy, the dentist attempts non-destructive removal, relying on breaking the bond of the luting cement rather than cutting the crown material. One common technique uses specialized ultrasonic tips applied near the crown’s margins.
The high-frequency vibration transmits mechanical energy through the crown, causing microscopic fractures in the cement layer. This action weakens the adhesive bond, allowing the restoration to be gently dislodged without damaging the crown material. However, this method is generally avoided with all-porcelain crowns, as the intense vibration can risk fracturing the ceramic.
Other specialized instruments apply a controlled, localized force to lift the crown off the tooth. Tools like pneumatic or manual crown removers engage the margin and use a precise lever action or controlled percussion force to break the seal. For instance, spring-loaded instruments deliver a short, rapid tap, while devices like the WAMkey use a cam mechanism inserted into a small gap to pry the crown vertically.
When the Crown Must Be Cut Off
When non-destructive methods fail, or if the underlying tooth has decay or a fracture requiring full visualization, the crown must be removed destructively. This technique involves sectioning the crown material using a high-speed dental handpiece and specialized burs. The goal is to create a channel through the crown to release internal stress, allowing the material to be fractured and removed in pieces.
For a porcelain-fused-to-metal (PFM) crown, the procedure uses a diamond bur to cut through the outer porcelain layer until the underlying metal coping is exposed. The dentist then switches to a tungsten carbide bur, which is more effective at cutting metal, to create a deep groove from the chewing surface down to the gum line.
With extremely hard all-ceramic materials like zirconia or lithium disilicate, the cutting technique requires different considerations. Zirconia is sectioned using fine-grit diamond burs. Typically, two grooves are cut on opposite sides of the crown, and a specialized instrument is then inserted into one of the grooves to gently wedge the crown apart, causing it to fracture and separate from the tooth.
The Next Steps for Replacing the Crown
Once the old crown is removed, attention shifts to the underlying tooth structure. The dentist cleans the remaining tooth, removing all traces of old cement and debris. An examination checks for decay, a common reason for crown failure, or any structural damage to the tooth.
Identified decay is removed, and the remaining tooth is prepared to support the new crown. This preparation may involve rebuilding a portion of the tooth with a restorative material, known as a core buildup. The tooth preparation is then refined, ensuring the correct shape and taper so the new replacement crown will fit precisely and securely.
Following preparation, an impression or digital scan of the newly shaped tooth is taken, along with a record of how the upper and lower teeth meet. This information is sent to a dental laboratory, where the permanent replacement crown is custom-fabricated. A temporary crown is then cemented onto the tooth to protect it while the patient waits for the permanent crown, typically one to two weeks.