A dental crown is a tooth-shaped prosthetic, often described as a cap, designed to fully encase a damaged or weakened tooth above the gum line. The primary purpose of this restoration is to restore the tooth’s original shape, size, and strength while also improving its appearance. Crowns are used to protect teeth that have suffered severe decay, large fractures, or extensive wear, ensuring the longevity of the natural tooth structure. The physical creation of this custom-made cap takes place in a specialized dental laboratory. This fabrication workflow requires extreme precision to ensure the final restoration fits seamlessly and functions correctly within the patient’s bite.
Capturing the Blueprint
The crown fabrication process begins with obtaining an exact measurement of the prepared tooth and the surrounding oral anatomy, which serves as the blueprint. Historically, this step relied on physical impressions, where a dentist uses a tray filled with a viscous material, such as alginate or silicone, to create a negative mold of the mouth. This traditional method requires careful handling and shipping to the lab, as the resulting impression is susceptible to distortion if not perfectly managed.
A modern alternative involves using an intraoral scanner, a handheld device that rapidly captures thousands of images of the teeth and gums. These images are then digitally “stitched” together by specialized software to form a highly detailed, three-dimensional model of the mouth. This digital impression is typically saved as an STL file, which can be instantly transmitted to the dental lab, eliminating the need for physical materials and shipping. Digital scanning offers high accuracy and enhances patient comfort by avoiding the sometimes unpleasant experience of traditional putty molds. The laboratory receives either the physical impression or the digital file, marking the end of the blueprint capture phase and the beginning of the crown’s creation.
Traditional Laboratory Creation
Once the dental lab receives a physical impression, the first step in the traditional workflow is to create a physical working model. Technicians pour a plaster material into the impression to create a positive replica of the prepared tooth, known as the die. This plaster model provides a stable, three-dimensional reference for the manual construction of the crown.
The next complex step, particularly for metal or porcelain-fused-to-metal (PFM) crowns, is the “wax-up,” which employs the ancient lost-wax technique. A technician sculpts the precise shape of the final restoration using dental wax directly onto the die. This wax pattern includes all the contours and occlusal details required for a proper fit and bite function.
For a full-metal crown or the metal substructure of a PFM crown, the wax pattern is encased in a heat-resistant investment material, creating a mold. The entire assembly is then placed into a furnace, where the wax is completely burned away, leaving a cavity inside the investment that is an exact replica of the crown. Molten dental alloy, which might include high-noble metals like gold or base-metal alloys, is then cast into this cavity.
If the crown is PFM, technicians apply layers of porcelain onto the cooled metal framework. Each layer of porcelain is fired in a specialized ceramic oven at high temperatures to achieve the correct shade, translucency, and strength. The final step involves applying a glaze layer and firing it one last time, giving the crown a smooth, lifelike finish.
The Digital Manufacturing Process
The digital workflow bypasses many of the manual steps involved in traditional crown creation. Digital scan data is imported into Computer-Aided Design (CAD) software, where a dental technician designs the crown geometry on a computer screen. This phase allows for precise adjustments to the restoration’s margins, contours, and bite surface.
Once the design is finalized, the digital file is transferred to a Computer-Aided Manufacturing (CAM) unit. The most common CAM method is milling, a subtractive process where a multi-axis machine carves the crown from a solid block of high-strength material. Common materials include Zirconia, lithium disilicate (E-max), or composite resin.
After milling, ceramic materials like Zirconia require a final, high-temperature heat treatment called sintering. Sintering transforms the soft, porous block into a dense, strong restoration. For aesthetic purposes, the crown may then undergo minimal manual finishing, such as the application of color stains and a final glaze. The crown is fired one last time to fuse the coloring and create a natural-looking surface.