Dental inlays and onlays are specialized, custom-made solutions used to repair teeth that have sustained damage beyond the scope of a standard filling. These restorations address moderate decay or structural compromise, bridging the gap between simple cavity repair and full tooth coverage. Often referred to as “indirect fillings,” inlays and onlays are fabricated outside the mouth before being bonded into place. This approach allows for a highly precise fit and offers superior strength compared to a traditional, directly placed filling.
Defining Inlays and Onlays
The distinction between an inlay and an onlay is based on the specific area of the tooth they cover. An inlay is a restoration designed to fit precisely within the cusps, which are the raised points on the chewing surface of the back teeth. It is used to repair damage centralized within the grooves of the tooth, similar to a traditional filling, but fabricated as a single solid piece.
An onlay is a more extensive restoration that covers one or more of these cusps, sometimes called a “partial crown.” Onlays are necessary when damage extends up and over the biting surfaces, providing coverage and reinforcement to weakened cusps. Both types of indirect restorations are commonly fabricated from durable materials, including porcelain, composite resin, or gold, with tooth-colored options popular for aesthetic appeal.
When These Restorations Are Necessary
Inlays and onlays are the preferred treatment when a dental cavity or fracture is too large to be reliably restored with a conventional direct filling. A standard composite filling may not provide sufficient structural integrity for extensive damage, potentially leading to the remaining tooth walls fracturing under chewing pressure. Indirect restorations are custom-made to precisely match the prepared area, offering a stronger, more stable solution.
These restorations are indicated when the tooth’s structure has been significantly compromised but does not require the complete coverage of a crown. They are designed to hold the remaining natural tooth structure together, dispersing biting forces more effectively than a large filling. This capability is beneficial for teeth that have sustained large areas of decay or those requiring restoration following a root canal procedure.
The Multi-Step Placement Process
Receiving an inlay or onlay typically requires two separate appointments because the restoration is fabricated in a laboratory, making it an “indirect” process. The first visit focuses on preparation and impression-taking. The dentist removes all decay or old filling material and meticulously shapes the remaining tooth structure to receive the custom restoration.
After preparation, a precise impression or digital scan of the tooth is taken and sent to a dental laboratory to serve as a blueprint. A temporary restoration is placed to protect the prepared tooth, prevent sensitivity, and keep surrounding teeth from shifting while the custom piece is crafted over the next one to two weeks.
The second appointment begins with the removal of the temporary restoration and a thorough cleaning of the tooth. The dentist checks the fit and bite of the permanent restoration to ensure it seats perfectly against the prepared surface. Once confirmed, the restoration is permanently bonded into place using a specialized dental adhesive, then polished and adjusted to create a smooth, seamless finish.
How They Differ from Fillings and Crowns
The primary distinction between inlays/onlays and standard fillings lies in their fabrication and inherent strength. Traditional (direct) fillings are sculpted and hardened directly in the mouth during a single appointment and are suitable only for smaller areas of decay. In contrast, inlays and onlays are fabricated outside the mouth, allowing for superior strength, a more precise fit, and greater resistance to shrinkage and wear.
Compared to a full dental crown, inlays and onlays are considered conservative restorations because they preserve more healthy tooth structure. A crown covers the entire visible portion of the tooth above the gum line, requiring the removal of significant natural enamel. Conversely, an inlay or onlay only restores the damaged part, making it a less invasive and often preferred option when sufficient healthy structure remains.