If a tooth has more extensive decay or structural compromise, a crown or onlay may be the ideal aesthetic and functional restorative solution.
Crowns and onlays are restorations that are fabricated outside the mouth, also known as “indirect restorations.” This is in contrast to restorations that are fabricated directly inside the mouth, colloquially known as a filling. Crowns and onlays are indicated for teeth with significant structural problems, such as cracks and teeth that have been heavily damaged by new or previous decay.
When a large old filling begins to fail, a crown or onlay will typically be recommended as the next restoration, especially for posterior teeth that are subject to higher chewing forces. The process of preparing the tooth for a crown or onlay greatly reduces the splitting forces on a tooth that result from the loss of tooth integrity following damage from large cavities.
Crowns and onlays are also made from materials that are stiffer and more wear-resistant compared to filling material, which contributes to the increased longevity of both the restoration and (more importantly!) the tooth beneath it.
Crown vs. Onlay?
The main difference between onlays and crowns is the number of tooth cusps that are covered or replaced. If all cusps are covered, the restoration is called a crown. If some but not all of the cusps are missing or weakened, a more conservative onlay restoration may be indicated.
When all cusps need to be covered, I still take the most conservative approach possible with your tooth. In the past, crowns involved shaving off nearly all the enamel from the tooth, 360º around (causing, on average, a 70% reduction of weight by volume of the crown of the tooth). This can be frankly and unnecessarily destructive to the tooth’s integrity when there are no defects in these regions. In years past, this was the only way to protect the tooth because we did not have strong and durable adhesive technology. With modern bonding techniques, we can create a long-lasting crown restoration and preserve more of your tooth while reducing the risks of post-operative sensitivity and tooth nerve complications.
Both crowns and onlays can be made from a variety of materials.
In the past, metal restorations and porcelain-fused-to-metal were commonplace. Modern approaches utilize porcelain materials that can bond to the underlying tooth structure. This creates a highly durable seal protecting the tooth below and restores the natural shape and function of the tooth. Porcelain restorations can be very strong and durable with the right techniques.
In fact, porcelain materials are the most similar to tooth enamel in their physical properties, making them the most ideal replacement for lost enamel. Nature, after all, is the best model for success. Porcelain restorations can be highly esthetic as they blend well with the surrounding tooth structure.
Crowns and onlays can generally be completed within a single, but longer appointment in our office thanks to our technology. In some cases, a tooth needs to be temporized on the first visit, and the final restoration is received at a future appointment. This is more common if we need to work with a lab to fabricate the restoration.