A dental crown, often called a cap, completely covers the visible portion of a damaged or weakened tooth above the gum line. Its primary function is to restore the tooth’s original size, shape, and strength while improving its appearance. Crown preparation, or “crown prep,” is the necessary first step, involving precisely reshaping the tooth structure. This reduction creates the required space for the crown material to fit over the tooth without appearing bulky or interfering with the bite. The success and longevity of the final restoration depend on the precision and quality of this initial procedure.
Clinical Reasons for Preparation
A dental crown is necessary when damage compromises a tooth’s structural integrity beyond what a standard filling can repair. This includes teeth with extensive decay that has removed too much healthy structure, leaving walls susceptible to fracture. Teeth previously restored with a large filling are prone to breaking, as the restorative material does not distribute biting forces as effectively as a crown. Fractured or cracked teeth need a crown to hold the compromised pieces together, preventing further propagation of the crack. Furthermore, teeth that have undergone root canal treatment are more brittle, making a crown a standard protective measure to shield the tooth from chewing forces. Teeth severely worn down from nighttime grinding, known as bruxism, may also require crowning to restore their proper height and function.
Detailed Steps of Crown Reduction
The procedure begins with a local anesthetic to ensure the patient is comfortable. Once the area is numb, the dentist uses specialized rotary instruments to begin the physical reshaping of the tooth, called reduction. This reduction must be carefully executed to remove the minimum amount of structure necessary while creating sufficient space for the chosen crown material, such as ceramic or metal alloy.
Occlusal and Axial Reduction
The reduction occurs in two main phases: occlusal and axial. Occlusal reduction involves removing material from the biting surface, typically 1.5 to 2.0 millimeters, ensuring the final crown will not interfere with the opposing teeth. Axial reduction addresses the sides of the tooth, reducing them by 1.0 to 1.5 millimeters to create slightly tapered walls. This tapering allows the crown to slide on and remain securely seated through friction and cementation.
Margin and Impression
A well-defined border, known as the margin or finish line, is established around the base of the tooth near the gumline. This margin must be smooth and continuous, often shaped as a chamfer or shoulder, acting as the precise seat where the edge of the final crown will rest. The integrity of this margin prevents microleakage of bacteria, which could lead to secondary decay beneath the crown. After shaping, a final impression is taken, either with putty or a high-resolution digital scanner, to create a blueprint of the prepared tooth. This impression is sent to a dental laboratory for fabrication of the permanent crown.
Before the patient leaves, a temporary crown is cemented onto the prepared tooth using a weak adhesive. This provisional restoration protects the sensitive tooth and prevents adjacent teeth from shifting position while the permanent crown is being made.
Navigating the Temporary Crown Phase
The temporary crown marks the interim period while the permanent restoration is fabricated. Patients may experience mild sensitivity to hot or cold temperatures following the procedure, which is a normal response to the tooth structure reduction. This sensitivity resolves quickly and can be managed with over-the-counter pain medication.
Since the temporary crown is held in place with a weak cement designed for easy removal, certain precautions are necessary to prevent it from becoming loose. Patients should avoid chewing sticky, hard, or overly chewy foods, such as caramel or hard candy, and chew primarily on the opposite side of the mouth. When flossing, slide the floss through the contact point and pull it out to the side, rather than popping it back up.
If the temporary crown comes off, patients must contact their dental office immediately to have it re-cemented. The temporary must remain in place to protect the vulnerable prepared structure and maintain the space required for the permanent crown. Once the permanent crown arrives, the patient returns for a final appointment where the temporary is removed and the final restoration is permanently bonded.