A dental onlay is a type of restoration used to repair a tooth that has experienced moderate damage or decay. This option is selected when the damage is too extensive for a standard filling but not severe enough to require the complete coverage of a full crown. Because it restores a significant portion of the tooth without encasing the entire structure, the onlay is often referred to as a “partial crown.” This method offers more structural support than a filling while preserving more natural tooth material than a full-coverage crown.
Defining the Dental Onlay
An onlay is a custom-made prosthetic designed to restore the shape, function, and strength of a damaged tooth. Its primary characteristic is that it covers one or more of the cusps, which are the raised points on the chewing surface of the back teeth. This differs from an inlay, which fits within the indented areas between the cusps. The onlay is considered an indirect restoration, meaning it is fabricated outside of the patient’s mouth, typically in a dental laboratory.
This indirect fabrication process allows the restoration to be crafted from solid, high-strength materials. The finished onlay is then permanently bonded onto the prepared tooth structure. By covering the weakened cusps, the onlay helps to absorb and distribute the forces generated during chewing. This protection is particularly beneficial for molars and premolars that bear the heaviest bite pressure.
Onlay Versus Fillings and Crowns
The choice between a filling, an onlay, or a crown depends on the extent and location of the tooth damage. A standard filling is a direct restoration, placed and hardened immediately inside the mouth, and is best suited for small to moderate areas of decay contained entirely within the grooves of the tooth. Fillings are not designed to cover or protect the tooth’s structural cusps.
The onlay is used when the decay or fracture extends up to or over the cusps, compromising the structural integrity of the biting surface. The onlay provides increased precision and strength because it is fabricated as a single, solid unit before being cemented.
A full dental crown represents the most extensive restoration. Crowns are reserved for cases where the tooth is severely compromised, perhaps due to a large fracture or following a root canal procedure. The crown covers the entire tooth structure above the gum line, offering comprehensive protection but requiring the removal of more healthy tooth material compared to the conservative approach of an onlay.
The Treatment Process
The procedure for receiving a dental onlay typically involves two separate appointments with the dentist. During the first visit, the dentist will numb the area and remove all existing decay and old filling material. The remaining healthy tooth structure is then carefully shaped to create a stable foundation that will securely hold the final onlay.
Once the tooth is prepared, a detailed impression or digital scan of the tooth is taken and sent to the dental lab for custom fabrication. A temporary onlay is then placed over the prepared tooth to protect it from sensitivity and damage while the permanent restoration is being made. Patients should treat this temporary piece with care, avoiding sticky or extremely hard foods.
The second appointment occurs once the custom onlay is returned from the lab. The temporary restoration is gently removed, and the final onlay is carefully fitted onto the tooth to ensure the bite is comfortable and the margins are sealed. After any necessary minor adjustments, the onlay is permanently bonded to the tooth using a strong dental adhesive.
Materials Used and Expected Lifespan
Dental onlays are fabricated using materials selected for their balance of durability and aesthetic appeal.
Material Options
Onlays are commonly made from the following materials:
- Porcelain or ceramic: These are frequently chosen for visible teeth as they can be precisely color-matched to blend seamlessly with the surrounding natural teeth.
- Gold alloy: Known for exceptional durability and resistance to wear, gold is often preferred for back molars where strength is prioritized over aesthetics.
- Composite resin: This offers a more affordable, tooth-colored option, though it may not possess the same fracture resistance as ceramic or gold.
High-quality onlays are considered a long-term solution, generally lasting longer than standard composite fillings due to their strength and custom fit. While the typical lifespan is often cited as 10 to 15 years, onlays made from porcelain or gold can frequently last 20 years or longer with proper care. Regular dental check-ups allow the dentist to monitor the restoration and maximize its functional life.