An inlay or onlay is a type of dental restoration known as an indirect filling, meaning it is fabricated outside of the mouth before being bonded to the tooth. These restorations are used to repair a tooth that has damage or decay too significant for a traditional filling but not extensive enough to require a full dental crown. They are custom-made pieces designed to fit precisely into the prepared tooth structure, restoring its function, shape, and appearance. This approach allows dentists to conserve a maximum amount of the natural, healthy tooth material while providing a durable repair.
Defining the Difference Between Inlays and Onlays
The distinction between an inlay and an onlay lies purely in the extent of the tooth surface they cover. They are custom-fabricated, often from materials like porcelain, composite resin, or gold, to ensure strength and an aesthetic match. The choice between them depends on the size and location of the damage within the tooth’s chewing surface.
A dental inlay restores the central part of the tooth, fitting within the cusps (the raised points on the chewing surface). Inlays are appropriate when decay is contained only in the grooves between these cusps, essentially filling a hole in the tooth’s center. They act as a strong, custom-fit filling for moderate-sized cavities that a direct composite filling cannot adequately support.
Conversely, a dental onlay is a larger restoration that extends beyond the valleys and covers one or more cusps. Onlays are sometimes referred to as partial crowns because they cover a significant portion of the chewing surface. This greater coverage provides structural support to a weakened tooth, especially if a cusp has been damaged or fractured. The onlay is selected when damage is too extensive for an inlay, but enough healthy structure remains to avoid a full crown.
When Dentists Choose Indirect Restorations
Dentists choose inlays and onlays when the situation falls between the need for a simple filling and a full crown. While standard fillings suit minor decay, a large or deep cavity requires an indirect restoration. Large traditional fillings compromise the remaining tooth structure and can lead to future fractures, but indirect restorations offer a superior, more durable fit and internal reinforcement.
The primary advantage over a full crown is the preservation of natural tooth material. Preparing a tooth for a full crown requires removing a significant amount of healthy structure. In contrast, inlays and onlays are a conservative approach, requiring the removal only of the decayed or damaged tissue, which helps maintain the tooth’s long-term strength.
The decision hinges on the amount of remaining tooth structure, particularly the health of the cusps. If the cusps are intact, an inlay is preferred. If one or more cusps are weakened or damaged, the greater coverage of an onlay provides the necessary reinforcement to prevent future breaks. These indirect restorations distribute chewing forces more effectively than large fillings, increasing the tooth’s strength by up to 75%.
The Multi-Step Procedure for Placement
Placement typically requires at least two separate dental appointments. The first visit focuses on preparing the tooth and taking a precise mold of the area to be restored. After administering a local anesthetic, the dentist removes all existing decay, old filling material, and weakened tooth structure.
Once the tooth is cleaned and shaped, a detailed impression or digital scan is taken. This mold is sent to a dental laboratory, where technicians custom-fabricate the final restoration for a perfect fit. Before the patient leaves, the dentist places a temporary restoration to protect the exposed tooth and prevent sensitivity while the permanent piece is made.
The second appointment occurs when the custom restoration returns from the lab, usually within a few weeks. The temporary restoration is removed, and the permanent inlay or onlay is placed to check its fit and ensure the bite is comfortable. After any necessary adjustments, the restoration is permanently bonded using a strong dental adhesive, often requiring a curing light to set the cement. The final step involves polishing the bonded restoration to blend seamlessly with the surrounding tooth structure.