Why did my dental crown fall off? 

Have you ever had one of your dental crowns come off? Why does that happen? There are actually quite a few reasons a crown can come off. Let’s look into what those are.

When a patient comes to me with a crown off, the first thing I ask is how long have you had the crown? If you have had the crown for a long time there are usually 3 reasons the crown has come off. The first is you may have some new cavity or decay starting under the crown. Cavities will destroy the good tooth structure under the crown and make it come loose. This means the best-case scenario is a new crown, the worst is an extraction if the decay is too extensive. The other option is if the crown has an open margin and was never properly sealed. Open margins allow saliva to seep in and eventually dissolve away the cement holding the crown on. If the crown has a poor seal then the best option is to make a new crown that does not have an open margin. The third option is the old cement just wore out. Nothing lasts forever and eventual cement can break down. If this is the case and the crown still fits well it can be recemented.

If the crown is newer then there are some other reasons that would cause a crown to come off. Like before, there could be an open margin leading to the cement washing out. Another reason has to do with how the tooth was prepared. To make sure a crown stays on we need 2 main things. We call them retention/resistance form and ferrule effect. What those terms mean is we need to shape the tooth in a way that prevents the crown from coming off and we need enough teeth to grab onto. When we shape a tooth for a crown we remove some tooth from the top and sides to allow the crown to slide into the prepared tooth. We want this prepared tooth to be as tall as possible and the walls of the tooth to be as parallel as possible. The prep would look similar to a top hat, with the brim of the hat being the margin the edges of the crown rest on and seal against, and the rest of the hat being the parallel walls and flat top of the rest of the prep. A tall vertical prep gives you a lot of teeth to grab onto and good resistance to chewing forces that try to push and pull the crown off. If your prepared tooth is too short or the walls are heavily tapered, this leaves us with less tooth to grab onto and less resistance to the pushing and pulling forces of chewing.

Poor preparation design can happen for 2 reasons. Sometimes the dentist has no choice. There are some times where the decay is so extensive we have to compromise our preparation design to try and save the tooth as opposed to extracting it, or your natural tooth is unusually short. If the prep is over tapered and too short and the decay was not particularly extensive then the problem is poor attention to detail by the dentist. Unfortunately, this is something I see more often than I would like to admit. Unfortunately, if someone has removed too many teeth we cannot get that tooth back. Therefore, trying to correct this can be a challenge and there is a combination of things we use to try and reshape the tooth. We will often drop our margins deeper below the gums to try and grab onto a more solid tooth structure. If possible we will try to reshape the walls to be more vertical. If that cannot be done then we will place vertical grooves into the tooth to make our own vertical walls to lock the crown on. 

Even with all these tricks, there are times where there is just not enough tooth to reliably work with and the only option is to remove the tooth and replace it with something like an implant or a bridge. A well-prepared crown should last you for many years. If you are having problems with a crown that came off or repeatedly comes off, please give us a call and we will be happy to go over the options of how we can properly restore your tooth.