In restorative dentistry, choosing between an onlay and a crown can significantly impact the long-term health and functionality of a patient’s tooth. Understanding when each treatment is appropriate can simplify the decision-making process, leading to better outcomes. In this educational overview, we’ll explore the key differences between onlays, crowns, and more modern crownlays, when to use each option, and how to effectively communicate these choices to patients.
An onlay is a type of indirect restoration that covers one or more cusps of a tooth but does not involve full coverage of the entire tooth structure. It is a conservative approach aimed at preserving as much of the natural tooth as possible. Onlays can be made from materials such as ceramic, composite, or gold. They are bonded to the remaining tooth structure, providing a strong, functional solution for restoring teeth that have suffered damage but retain enough healthy tooth material.
A crown, on the other hand, involves full coverage of the tooth, encasing it entirely to protect and restore its function. Crowns are typically used when the tooth is significantly compromised, either due to decay, fracture, or after procedures like root canal therapy. They are made from various materials, including porcelain, zirconia, and metal alloys, depending on the aesthetic and functional needs of the tooth.
The choice to place an onlay often arises when a tooth has some structural damage, but enough healthy material remains to support a more conservative restoration. The aim of an onlay is to preserve the natural tooth while restoring strength to weakened areas. Onlays are ideal when:
In many cases, onlays offer a more flexible treatment plan as they can be tailored to the specific needs of the tooth. Dr. Michael Frazis points out that there is no single "right" onlay preparation, as each case varies depending on what parts of the tooth are broken or likely to break. The goal is always to remove what’s broken and prepare space for the restorative material.
Onlays also preserve the natural flexibility of the tooth by reinforcing weakened areas without eliminating healthy structure. The benefit of bonding the restoration directly to enamel and dentin helps maintain strength and reduces the risk of further fractures.
A crown becomes necessary when the structural integrity of the tooth is more significantly compromised. This is often the case in situations like:
Crowns provide a predictable solution for teeth that require extensive support. By fully encasing the tooth, a crown can prevent further damage, protect against fracture, and restore full chewing function. In cases where structural integrity is critical, such as cracked teeth or after extensive decay, crowns offer a secure, long-lasting solution.
As Dr. Frazis notes, crowns are particularly beneficial when a tooth has multiple compromised cusps or cracks running throughout its structure. The "ferrule effect" of a crown, which involves creating a 360-degree margin around the tooth, adds significant stability and prevents future breakage by reinforcing the tooth’s remaining structure.
A crownlay is a more modern hybrid between a crown and an onlay. You essentially cover the full occlusal aspect of the tooth but only extend down the sides as far as is required for the material. Like an onlay for the whole tooth. They protect the tooth like a crown but rely on bonding and are more conservative like an onlay. They can be used instead of a traditional crown but as they do rely on bonding more than a traditional crown there can be cases where one is better than the other. It’s never a 'one size fits all' approach with dentistry.
If over 50% of the tooth is intact and the damage is isolated to one or a few cusps, an onlay is often a better option. If most of the tooth is compromised, a crown will provide more comprehensive protection.
For patients with a history of bruxism or heavy occlusion, a crown may be necessary to withstand the forces of chewing. Onlays are ideal for less extensive damage but may not always provide the same level of durability in high-stress areas.
Onlays are more conservative and may appeal to patients who prioritize preserving their natural teeth. Crowns, while more invasive, offer the peace of mind of full protection for more severely damaged teeth.
Both onlays and crowns can be made from durable materials like ceramic or zirconia, but the decision may be influenced by aesthetics, especially in the anterior region, or by the need for stronger materials like metal in posterior teeth.
One of the challenges in restorative dentistry is effectively communicating these options to patients. Dr. Frazis emphasizes that patients do not need to be burdened with overly technical language. Instead, focus on explaining the benefits of each option in terms of functionality and preservation of their natural tooth.
Giving the patient the best option for the tooth sets the scene so they know what the best possible option is whether it’s a crown or an onlay.
For example:
“Mrs Jones your tooth ideally needs a crown to hold it together, if you can’t afford one we can do a large plastic filling instead to buy us a little more time”
"An onlay allows us to keep most of your tooth intact while reinforcing the parts that are damaged."
"A crown will fully protect your tooth, ensuring it stays strong for many years."
By simplifying the discussion and focusing on outcomes, you can build patient trust and help them feel confident in the treatment plan.
Knowing when to opt for an onlay versus a crown - or a modern crownlay - is a key aspect of restorative dentistry. Onlays offer a conservative, flexible option for restoring damaged teeth while preserving natural structure, whereas crowns provide full coverage for teeth that require more extensive protection. A crownlay is a more modern hybrid between a crown and an onlay. By assessing each tooth’s unique needs and discussing options with patients in clear, straightforward terms, clinicians can make informed decisions that promote long-term dental health.
This decision-making process, combined with advanced material selection and careful treatment planning, ensures that patients receive the most appropriate and effective care for their needs.
Want to learn more? Dr. Michael Frazis covers how to quickly determine if a tooth requires an onlay or a full traditional crown in his latest masterclass 'Onlays vs Crowns: Which To Do When'. Get free instant access to the full Masterclass here.
Not confident in your onlay skills? Learn to design onlay and overlay restorations that restore proper function and esthetics as part of the Fellowship in Restorative Dentistry. Learn more about the Fellowship by downloading the brochure here or chat with our team here.