A dental crown is a tooth-shaped cap placed over a damaged tooth to restore its shape, size, strength, and appearance. Since a permanent crown is custom-made in a dental laboratory, it often takes several weeks to complete. During this waiting period, a temporary crown is placed to protect the prepared tooth, ensure comfort, and maintain appearance. The temporary restoration acts as a placeholder, preserving the space and function of the tooth until the final cap is ready for seating.
The Necessity and Composition of Temporary Crowns
A temporary crown serves several important functions. The underlying tooth structure, stripped of its protective enamel during preparation, is vulnerable to sensitivity, especially to temperature changes and air exposure. The temporary restoration seals off the exposed dentin, preventing discomfort and protecting the dental pulp from bacterial contamination.
The temporary crown is also crucial for maintaining the precise positioning of teeth. Without a placeholder, adjacent teeth can drift into the open space, and the opposing tooth can shift or “super-erupt,” preventing the permanent crown from fitting correctly. These restorations help maintain proper bite alignment, or occlusion. Temporary crowns are typically made from less durable materials than their permanent counterparts, commonly using acrylic resins like polymethyl methacrylate (PMMA) or bis-acryl composite materials. Bis-acryl composites are preferred for custom-made temporaries due to their improved aesthetics, lower heat generation during setting, and reduced shrinkage compared to traditional acrylics.
Initial Tooth Preparation
The process of creating a custom temporary crown begins with the dentist shaping the original tooth to accommodate the permanent restoration. Before the tooth is reduced, the dentist takes a preliminary impression of the tooth and the surrounding area. This impression, often made with vinyl polysiloxane or alginate, serves as the matrix used to form the temporary crown.
The tooth is then reduced, or “prepped,” to create adequate space for the crown material without compromising its structural integrity. This reduction involves removing tooth structure from the chewing surface (occlusal reduction) and the sides (axial reduction). Typical reduction amounts range from 0.7 mm to 2 mm, depending on the final crown material planned.
A clearly defined finish line, or margin, is established at the gum line to ensure a precise seal for both the temporary and permanent crowns. Common margin designs include a chamfer or a shoulder, which must be smooth and continuous to prevent bacterial leakage and irritation to the gum tissue. This preparation creates a slightly tapered shape, necessary for the final crown to slide into place and be cemented securely.
Fabricating and Seating the Temporary Crown
Fabricating the custom temporary crown directly in the patient’s mouth is known as the direct technique, relying on the pre-preparation impression taken earlier. The temporary material, often a self-curing bis-acryl composite, is mixed and loaded into the impression matrix. It is dispensed from a specialized cartridge, ensuring the correct ratio of base and catalyst for a reliable setting reaction.
The material-filled matrix is immediately seated over the prepared tooth, ensuring it is fully positioned and adapted to the new tooth shape. As the material begins polymerization, it is held firmly in place for a few minutes until it reaches a rubbery consistency. The dentist then removes the matrix, leaving the semi-set temporary crown material on the prepared tooth.
Once the material is hardened, the temporary crown is removed from the tooth to begin the adjustment phase. Excess material, known as “flash,” is trimmed away using dental burrs and scissors to establish clean margins that fit precisely at the gum line. The dentist then contours and polishes the restoration to ensure a smooth surface that will not irritate the tongue or gums. Finally, the temporary crown is cemented onto the prepared tooth using a specialized temporary cement, designed to hold the crown securely while remaining easy to remove later.
Maintaining and Removing the Temporary Restoration
Caring for the temporary crown requires adjustments to the patient’s normal routine to ensure it remains intact until the permanent crown appointment. Patients should avoid sticky or hard foods, such as caramels or nuts, which can pull the temporary crown off or cause it to fracture. Chewing should primarily be done on the opposite side of the mouth to minimize stress on the restoration.
While regular brushing is encouraged to maintain gum health, flossing around the temporary crown requires a modified technique. Instead of pulling the floss back up through the contact point, which could dislodge the crown, the patient should slide the floss through and then pull it out from the side. If the temporary crown comes loose, contact the dental office immediately, as the exposed tooth is vulnerable to sensitivity and shifting.
When the permanent crown is ready, the dentist removes the temporary restoration by grasping it and breaking the seal of the temporary cement. This cement is designed to be weaker than permanent cement, allowing for removal without damaging the underlying tooth preparation. After cleaning the tooth, the permanent crown is seated and bonded into place.