Archives for September 2013

Dental MythBuster #9 – You can’t get a cavity under a crown

This is one dental myth that I wish I did not have to see.  The myth typically plays out like this:

“Mrs. Jones, I can see both on the x-ray and upon clinical exam that there is decay on this particular tooth.”

She will typically respond by saying:

“How can I have a cavity on that tooth? It has a crown!”

After years of practicing dentistry, I can say that this happens about 98% of the time when there is decay on a tooth which already has a crown. So this dental myth definitely needs to be busted!

Photograph of a cavity under a crown

Seeing is believing, so let’s take a look at a photo I took of a patient in my dental office in Orange, CT.

Photo showing a cavity, also known as dental decay, under a dental crown

A cavity, known more formally as dental decay, evident underneath a crown on a lower molar on a patient of mine in Orange, CT.

The decay is visible in the above photo at the gum line. Treatment will most likely involve a new crown. Without treatment, this patient will lose his tooth eventually.

By looking at the photo, you can see that it is possible to get decay under a crown. So the myth is busted! But let’s look at how it happens.

What are dental cavities?

Dental decay photo showing a cavity on an upper canine tooth

Decay on an upper canine near the gum line.

Dental decay (known less formally as dental cavities) occurs when bacteria inside the mouth ingest certain foods and then attack the teeth. This leads to a weakening of the tooth and can ultimately lead to an actual hole (a.k.a cavity) in the tooth.

Decay can occur on any part of any tooth in the mouth. It can occur on teeth that have never had a filling before. Or the decay can start on teeth that have had fillings, crowns, or root canals.  It can start at age 2 or age 100! For a more detailed explanation, you can refer to a page I authored on my main practice website.

How teeth with dental crowns can develop decay

As stated earlier, decay can develop on any tooth. But cavities are more likely to occur in certain areas.

Dental x-ray radiograph showing decay or cavities under or below a dental crown

The red circles indicate the decay at the margin of two different crowns.

When it comes to teeth with crowns, the area most susceptible to developing decay is the margin. The margin, as you would guess, is where the crown meets the tooth. It is the weak spot. It is the Achilles Heel.

Food and other debris can collect right at the margin. A crown that was poorly made will collect even more food. If you combine this with a diet rich in sugar or acid, along with home hygiene that is not ideal, you have a perfect storm. That perfect storm affected the two crown to the upper right on the x-ray, resulting in decay.

Another Dental Myth Busted

The above photos, descriptions, and x-ray show that even with a crown, a tooth can still develop a cavity. So it bears repeating:

Crowns will protect an already weakened tooth but you still need to brush and floss sensibly. If you don’t, you can develop decay just like you would on any other tooth.