When a tooth sustains damage from decay or fracture that exceeds the limits of a simple repair, restorative dentistry offers solutions. While minor cavities are easily addressed, more extensive compromise to the tooth structure requires a restoration that can bear significant chewing forces and provide long-term protection. Dental onlays represent an intermediate option that conserves healthy tooth material while delivering the durability needed for a lasting repair. This approach ensures the tooth can withstand the stresses of daily use, preventing further structural failure.
Defining Dental Onlays
A dental onlay is a custom-made restoration used to repair a tooth damaged by fracture or decay, typically on the chewing surface of a molar or premolar. Fabricated in a laboratory as a single, solid piece, it is distinct from direct fillings placed immediately in the mouth. The onlay’s design is characterized by its coverage of one or more cusps, which are the raised points on the tooth’s biting surface.
Because an onlay covers these cusps, it is sometimes described as a partial crown, restoring more surface area than a standard filling but not fully encasing the tooth. The onlay helps to reinforce the tooth against the heavy forces exerted during chewing, particularly when a cusp has been weakened or removed due to extensive damage.
Onlays Compared to Traditional Restorations
Traditional fillings are placed directly into the prepared cavity and are suitable for smaller areas of decay contained within the tooth structure. For more extensive damage, fillings may not provide sufficient reinforcement, leading to a risk of fracture.
An onlay is structurally distinct from an inlay, though both are indirect restorations fabricated outside the mouth. An inlay is designed to fit within the cusps, restoring the area between the points of the chewing surface. Conversely, an onlay is necessary when the decay or damage has extended to and necessitates the replacement of one or more of the cusps.
The difference between an onlay and a full crown relates to the degree of tooth structure removed and covered. A crown fully encases the entire visible surface of the tooth above the gum line. The onlay, often called a partial crown, is a more conservative treatment because it covers only the damaged area and the compromised cusps, allowing the dentist to preserve significantly more of the healthy, natural tooth structure. Retaining healthy enamel and dentin is associated with better long-term tooth health.
The Onlay Placement Procedure
Receiving a custom-fabricated onlay typically involves two separate appointments. The first visit focuses on preparing the tooth. During this appointment, the dentist administers a local anesthetic before carefully removing all decayed or damaged tooth material.
Once the tooth is cleaned and shaped, a detailed impression or digital scan is taken to create a precise mold. This impression is sent to a dental laboratory, where technicians custom-fabricate the permanent onlay to match the tooth’s exact contours. To protect the exposed tooth structure while the restoration is being made, the dentist places a temporary onlay.
The second visit occurs once the permanent onlay has been returned from the laboratory. The temporary restoration is removed, and the underlying tooth is cleaned and prepared for final bonding. The dentist then checks the custom-made onlay for a flawless fit and proper bite alignment before permanently bonding it to the tooth structure using a strong dental cement or resin. Final polishing completes the restoration.
Materials and Expected Lifespan
Dental onlays are fabricated from several different materials. Porcelain, or ceramic, is a popular choice because it can be precisely color-matched to the natural teeth, providing an aesthetic, nearly invisible restoration. Composite resin offers another tooth-colored option, which is more affordable. For maximum strength and longevity, gold alloy remains a highly durable material, though it is typically reserved for back molars where aesthetics are less of a concern.
The expected lifespan of an onlay is substantial, often lasting 10 to 30 years. Consistent oral hygiene is necessary to protect the margins where the onlay meets the natural tooth. Maintenance steps include:
- Brushing twice daily and flossing.
- Avoiding habits like chewing on hard objects or ice.
- Attending regular dental checkups.