Conserving Tooth Structure: Onlay vs. Crown?

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

One of the aspects of good dentistry involves the conservation of tooth structure; that is, we always want to restore the tooth in question by removing only the decay, existing defective restorations, and undermined tooth structure, while maintaining the integrity of the rest of the tooth.  When it comes to restoring teeth with cuspal involvement (Figure 1), 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).  An onlay is an indirect restoration fabricated usually from either porcelain or gold, and is cemented onto a tooth that requires cuspal replacement.  A crown can be seen as an onlay that covers all the cusps.

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.

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.

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.

As you can see, both of these treatment options help to restore broken cusps, but the crown option requires the removal of more tooth structure to allow the crown to fit circumferentially around the tooth.  Conservation of tooth structure is important because every restoration will eventually break down over many years due to the exertion of high chewing forces, and when the restoration fails, new decay/cavities will form around and under that defective restoration.  In order to replace this defective restoration, 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 and when 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 so when the initial onlay does break down, there is still plenty of tooth structure to perhaps render a crown.

Over the years, insurance companies have arisen to prevalence and have, in many ways, 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, and consequently, many dental providers may opt to render the crown as the treatment option, as crowns are almost always a covered benefit.  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, as the consequence of undergoing a less desirable option now could lead to a more expensive and involved treatment in the future!


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