Updated: Oct 14, 2022
It is certainly possible to get decay underneath a crown even if it has had a root canal. Don't forget that a cavity can form on any surface that has natural tooth structure. The crown may be covering over the top layer but underneath of it is still your actual tooth.
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Tooth decay under crown with a root canal
Yes, it is possible to get decay underneath a crown even if it had a root canal. The root canal itself does not prevent future decay. As a matter of fact, the root canal procedure does not remove any tooth decay at all. The whole purpose of the procedure is actually to just remove the pulp of the tooth. The root canal specialist will remove the nerve from the tooth and then return the patient to their general dentist for the full cavity removal.
Your general dentist will complete the cavity removal or at least to the best of their ability before putting the crown on for you. Once again, just because the tooth had a root canal and it is dead, it does not make it immune to cavities. Even with the crown put on, it can still get a new cavity.
The only difference is that the crown itself cannot get a cavity but the tooth underneath of it can still get a cavity.
Why does the porcelain crown not get a cavity?
The porcelain is unable to get a cavity because the acid that the bacteria eats from the sugar in your mouth is unable to melt through the porcelain. The acid from the bacteria is very acidic but is still unable to penetrate through the porcelain. Similar to how you can have very acidic food on your porcelain plate and it won't melt it.
Have you ever had spicy food or something acidic go through a ceramic plate? Most likely not. However if you were using a paper plate, it can go through. The porcelain is just a lot sturdier than the paper. Your crown tooth uses a similar type of porcelain.
This is the reason why the tooth cap itself is immune but unfortunately you cannot wrap the root of the entire tooth in porcelain. The bacteria can sneak in at the margin of the crown, which is where the porcelain meets your natural tooth structure.
How does decay get under the crown?
There is always a gap somewhere along the gum line where your crown ends that the bacteria can cause a cavity. Most of the time your dentist will place the margin of the crown below the gumline but not everyone brushes at the gumline and thus plaque often gets left behind.
Plaque contains a lot of bacteria so if they are left underneath the gumline, they are basically positioned right underneath the crown. If you eat a sweet meal and provide the bacteria with some sugar, they will produce acid that can lead to decay under the crown over time.
It won't happen overnight but the acid from the bacteria will slowly eat through the tooth to form a cavity.
How to prevent decay under crown?
It is very simple to prevent decay under a crown because all you have to do is be strict with your oral hygiene regime. In addition to the brushing and flossing, make sure you minimize the amount of sugar that you eat throughout the day. If there is no sugar, there is no fuel for the bacteria to cause any tooth decay.
Aside from sugar you should also avoid foods that will cause an acidic environment in your mouth. Cavities don't start forming until the pH gets below 5.5 which is also called the critical pH level.
So just to recap on how to prevent decay underneath a crown:
Brush and floss twice a day.
Use a fluoride toothpaste.
Minimize sweet, sour, and acidic foods in your diet.
The short answer is yes, you can get a cavity underneath of your crown even if it had a root canal. The root canal and crown does not preclude your tooth from future decay. The bacteria can sneak in underneath the gap between the crown and the gums to cause a cavity.
Whenever you get a cavity on a tooth that has already had it before, it is called recurrent decay. The name implies that it is not the first time.
Last but not least, don't forget to go in for your 6 month dental check ups and cleaning with your favorite dentist in long island city! If you happen to catch problems early, you can have them treated more conservatively. It'll also be less expensive for you as well.