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My Zirconia Crown Keeps Coming Off

A zirconia crown that keeps coming off is a tell-tale sign of it having poor retention and the only way to fix it is by redoing it with better retentive features.


zirconia crown on stone model
zirconia crown on stone model

Table of Contents:


Reasons for poor retention

If the zirconia crown is not staying on the tooth despite being glued on, it most likely has problems with its retention.


Causes of poor retention:

  • Short clinical crown

  • Over tapered axial walls

  • Poor cement choice

  • Heavy lateral excursive forces


Short clinical crown

A very short tooth will make it incredibly difficult for your zirconia crown to stay on. The reason is because the retention of the restoration is directly proportional to the surface that it has in contact with.

  • A bigger tooth will have a larger surface area for the crown to grab on to.

  • A smaller tooth will have a smaller surface area for it to grab on to.


short clinical crown

Basically the larger the surface area the more surface friction the glue will have to hold the crown on. You lose a lot of this benefit when the tooth is short.


normal sized clinical crown
normal sized clinical crown

Video demonstration

If it's hard for you to visualize using words, we've created a video to show what we mean by having a short clinical crown.



Essentially, a longer or larger tooth will provide better retention. That means the crown will be less likely to pop off.


Over tapered axial walls

Crowns have the best retention when the axial walls are less tapered. If they are over tapered and have a high degree of convergence, the retention will consequently suffer.


various crown preparation degrees of taper
Crown prep degrees of taper; Credit: E. Emtair, S. Bakry, A. Azer

Studies have shown that the ideal degree of convergence is 5 degrees. Once the taper starts increasing beyond that point, the crown will have a harder time staying on the tooth. In other words, it will come off more easily.


Wrong cement choice

The most popular type of dental cement that is used for zirconia crowns is resin modified glass ionomer (RMGI). It is versatile and works extremely well for most situations.


However for a non-retentive situation where it keeps coming off, you need a stronger cement. A better choice would be an all resin cement which is typically reserved for veneers. Using it on zirconia does not give it the full benefits but it is still nonetheless stronger than the RMGI.


Heavy lateral excursive forces

Zirconia tooth caps can get knocked off the tooth if there are heavy lateral excursive forces. This type of force isn't the up and down biting that you do when you chew. What we mean by this is the side to side motions.


If there are a lot of side to side interferences, it only increases the chances of it popping off. This may happen if your dentist didn't check the side to side occlusion.


How to increase zirconia crown retention

All hope is not lost because there are ways to increase the retention of your zirconia tooth cap. These all require a trip back to your dentist to implement it.


Ways to increase zirconia crown retention:

  • Adding retention slots

  • Using a stronger cement

  • Decrease taper of axial walls

  • Adjust the occlusion


Add retention slots

An often glossed over technique to improve crown retention is to add slots to the crown preparation. Basically your dentist will drill a small rectangular box into the buccal (cheek side) and lingual (tongue side) of the tooth. These additional slots will add retention to the crown and help it stay on.



This technique will increase the surface area that the crown has in contact with the tooth. It will also increase the effectiveness of the dental cement.


Stronger cement

If your dentist didn't use the strongest cement possible, they should consider it now since it has fallen off a few times. The glue of choice would be an all resin cement that is typically used for dental veneers.


Decrease taper of axial walls

If the lack of retention from your zirconia crown was due to over tapered walls, your dentist can decrease the taper by reprepping it. Basically they will redrill around the tooth and make the axial walls straighter.


Adjust occlusion

After cementing the crown back on, it would be prudent for your dentist to check the occlusion. Make sure it is not being occluded heavily on nor are there lateral interferences.


If you're hitting on that tooth hard when you chew, it'll only increase the likelihood of it popping off again. These high spots will need to be shaved down.


Alternatives

If none of the recommendations above work and the zirconia crown continues to come off, you should consider alternative options. Perhaps zirconium dioxide is not the best choice of dental material for your particular situation.


Switch to emax crown

Your dentist could switch ceramic materials to emax instead of zirconia. The biggest benefit of using an emax crown is the ability to bond it onto the tooth. This type of ceramic material is more similar to a veneer where it can be bonded. Zirconia on the other hand lacks the capability to be bonded because it can only be cemented.


Dental implant

If no crown can stay on, perhaps you should consider getting a dental implant. Of course you would need the tooth to be extracted first but afterwards you can get a zirconia implant crown that is screwed in.


For a screwed in implant crown you don't have to worry about the glue coming loose. The retention will instead rely on the screw.


Takeaway

Crowns coming off is not an uncommon complication from getting a dental crown. The challenges are increased if you opt for zirconia instead of emax since it cannot be bonded.


Nonetheless there are a couple of things which you can try to help improve the retention. We recommend discussing with your dentist about what your options are and what you should do.

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About the author: Dr David Chen, DDS

Hello, I'm Dr Chen and I'm an actively practicing dentist in Long Island City, NY. I graduated from Columbia University College of Dental Medicine in 2016 but prior to going to dental school I was already working in the dental field. It's been more than a decade since I first got to know dentistry and let me tell you, time flies by quickly. Since then I've developed a fondness for writing, which is how this all got started!

Association Memberships:

Medical Disclaimer:

This blog is purely meant for information purposes and should not be used as medical advice. Each situation in your mouth is unique and complex. It is not possible to give advice nor diagnose any oral conditions based on text nor virtual consultations. The best thing to do is to go in person to see your dentist for an examination and consultation so that you can receive the best care possible.

The purpose of all of this oral health information is to encourage you to see your dentist and to inform you of what you may expect during your visit. Due to the unfortunate nature of dentistry, there isn't really any true home remedies that will get rid of dental problems. Roughly 99.99% of them require in-person intervention by a healthcare professional.

Hint: That is the reason why you can't eliminate seeing dentists in your life!

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