Conserving Tooth Structure: Onlay vs. Crown?

Posted by: Jason Hui, DDS, on April 9, 2013

Recently updated on July 14th, 2022 at 10:18 pm

Onlays and crowns are the two main treatment options for restoration of a damaged tooth. Crowns are much more popular, but in many cases they are not the best option. Here at Paragon Dentistry, as your local trusted dentist in Allen, TX, we always recommend the optimum choices for patients. So let’s explore what each one involves and how to decide which is best.

Onlays and Crowns What They Are Used For

Dental restoration using a crown or onlay is the  restoration of function and appearance of a damaged tooth. The damage can be caused by decay, cracks or other injury to the tooth.

Onlays and crowns are used to restore teeth with cuspal involvement (Figure 1). A cusp is an elevated part of the tooth. Typically, this refers to molars, which usually have four cusps.

Onlays and crowns are the usual treatment options because the cuspal areas require extra strength since they are the predominant contributors to masticatory function (chewing).

broken tooth causing pain and needs crown or onlay
Figure 1. The black arrows indicate intact cusps; the blue arrow indicates a cusp that has broken off. A case like this will require either an onlay or a crown to restore the broken cusp.

What is an Onlay

An onlay is a fabricated piece of porcelain or other material which replaces a damaged cusp. The onlay is cemented onto a portion of the top of the tooth. In other words, it lays on the top surface of the tooth. Figures 2a, 2b, and 2c show examples of onlays.

chipped and cracked tooth needing porcelain onlay or crown
Figure 2a. This is an example of a porcelain onlay covering two cusps of the tooth. Note that this onlay is made with unique color and staining to match the natural tooth in the patient’s mouth.
conservative dental treatment in allen tx for a broken tooth is porcelain onlay
Figure 2b. This image illustrates the coverage of one cusp by a porcelain onlay.
cosmetic tooth colored onlay to fix chipped back tooth
Figure 2c. This image illustrates the coverage of one cusp by a porcelain onlay.

What is a Crown

Crowns are similar, being a fabricated piece of porcelain or other material. However, a crown will cover the entire tooth. A crown can be seen as an onlay that covers all the cusps, except that it is not just on the top surface.

Figure 3a shows a crown, and 3b shows how the crown would fit like a cap over the entire damaged tooth.

best high quality porcelain crown in allen and plano tx
Figure 3a. This image reveals an all-porcelain crown; the entire chewing surface of the tooth will be covered by this crown so that no natural tooth is exposed in the mouth.
broken tooth needs a dental crown or cap
Figure 3b. In order for the crown in Figure 3a to fit over the existing tooth, the tooth needs to be cut down circumferentially as seen in this image to accommodate the crown over the entire tooth.

What Materials Are Used to Make Onlays and Crowns

As mentioned, both onlays and crowns are usually made of porcelain. Gold used to be a popular material, but nowadays people prefer to restore the natural look of a tooth. Porcelain comes closest to a natural tooth. Porcelain can also be bonded to precious metals to increase its strength. Ceramic and resin are other possible options.

What are the Pros and Cons of Onlays vs Crowns

Both onlays and crowns require a similar procedure. An impression will be taken during the first visit, with a temporary onlay or crown being fitted. The permanent onlay or crown is created by a lab, so a second visit is required for fitting.

Crowns are usually slightly more expensive, but they tend to last a little bit longer. Of course, many factors influence the longevity of both crowns and onlays.

However, a crown requires a bit more work. In order for the crown to fit over the tooth, a fair amount of tooth structure is removed. Moreover, removing part of the tooth unnecessarily is something we try to avoid, if at all possible.

Conservation of tooth structure is important because every restoration will eventually break down. Over many years, due to the exertion of high chewing forces, the restoration fails. New decay/cavities will form around and under the crown.

In order to replace this crown, more tooth structure will need to be removed due to new tooth decay.  If we aggressively and unnecessarily remove tooth structure during the time of the first restoration, there may not be sufficient tooth structure to support a second restoration. If this occurs, the tooth is deemed non-restorable and will require extraction. 

Onlays help patients avoid the eventual need for more extensive treatment with dental bridges or dental implants by conserving healthy tooth structure. When the initial onlay does break down, there is still plenty of tooth structure to perhaps render a crown.

How to choose between an onlay or a crown

Onlays are suitable to restore a tooth with limited damage. Replacing one or two cusps is normal. However, if there is too much damage or decay in the tooth, a crown may be the only option. In other words, sometimes the decision is clear.

Other times, the decision is more difficult. Over the years, insurance companies have begun to dominate dental treatment.  Many patients may elect only to undergo procedures that are covered by their insurance plan and forgo all procedures that are not.

In reality, what insurance companies pay or don’t pay for has no correlation with what treatment is necessary or best for the patient’s dental health. In the case of onlays vs. crowns, most insurance companies fail to include onlays as a benefit.

Consequently, many dental providers may opt for the crown as the treatment option, since crowns are almost always a covered benefit. While this may be better in the short-term for the patient, at least financially, it may not be the best long term for overall dental health.

Here at Paragon Dentistry, we like to encourage a long-term perspective and advocate doing the best treatment for your teeth as recommended by your dental professional. The consequences of undergoing the cheaper option now could lead to a more expensive and involved treatment in the future.

We understand that personal finances are always going to be part of a patient’s decision making. So ultimately, we allow you, the patient, to make the final call. We simply try to present you with the facts and give you our expert opinion.

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The Paragon Dentistry team would like to invite you to experience the difference at our practice while restoring yourself to optimal dental health!

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