Month: January 2017

A Crown? How did this happen?

I can’t say I have ever had somebody tell me that they were excited to hear that they needed a crown.  At least not a dental crown.  Who knows why someone decided to call it a crown anyways.  They don’t look like any real crown I have ever seen.  They don’t make you a royal (although, wouldn’t that be cool).  I have seen some with jewels in them, but that probably isn’t what you are looking for.  You may have also heard them called “caps”.  The technical term is really “full coverage indirect fixed restoration”.  I suppose that was a bit a mouthful, so crown was just easier.

There are many reasons people need crowns, but the most common reason stems from weakness or cracks in the surface of your tooth.  That may be from biting something hard at the wrong angle.  It could also come from past large fillings in your teeth.  It also happen in teeth that have just been weakened by your chewing pattern and the way your teeth come together.  If you have had a root canal on a premolar or molar, a crown is needed because the tooth has been largely hollowed out in the middle and will fracture into the root without one.

The most common instance we see for needing a crown is on teeth that have large, and usually older, fillings in them.  I often use the analogy of a house when talking about what leads up to the need for a crown.  Our tooth starts out as a house with walls and a roof.  When large fillings have to be placed in the middle of teeth, we are essentially removing the roof of the house.  Those walls no longer have a structure that reaches from one side to the other to hold them together.  They are still bolted to each other at the corners, but just don’t have the support on top anymore.  The force of chewing on our back teeth in sideways directions puts stress on those connections between the walls of the house.  Often times the fillings that have been placed also disrupt one or more of the walls of the tooth as well.  So that leaves some of the walls only connected to another wall on one side.  Over time the stress of chewing eventually creates small cracks between the walls, and leaves them standing on there own.  At this point, they may not break off completely, but are now only bolted to the floor.  You can imagine that it takes a lot less force to push on a wall of a house and knock it over if it is only bolted to the floor.


When these cracks develop, most of the time we don’t know how bad they are.  We may see small cracks that are only superficial.  Sometimes a piece of the tooth just breaks away.   There is something we call “Cracked Tooth Syndrome” where patients will tell us they get a zing in their tooth when they bite on something hard.  It goes away quickly, but is an indication that the tooth is flexing at the crack.


When any of these things happen, we need to do something to protect what is left of the tooth and keep it from falling apart completely.  If a piece has already broken away, the crown will help to strengthen what is left and replace the missing tooth structure.  Fillings can replace missing tooth structure too, but don’t tend to fare as well long term when there is no wall to help support them.

Crowns are a little like the metal ring around a wood plank barrel.  Those planks don’t want to stay together, but the ring has equal and opposite forces pushing against each plank from around the outside.  This keeps the barrel together and strong.  That’s called the Ferrule Effect, probably named after some really smart Physics Professor somewhere.  Crowns fit so precisely and are so strong that they can keep the rest of the tooth from falling apart, and are cements are so good now that they help increase strength as well.

Crowns are most often made from tooth colored material now.  Used to be we mostly used porcelain that was baked onto an under surface of metal.  Those crowns look better than a gold one, but still often show some darkness from the metal around the edges.  The vast majority of the time now, we use materials in our crowns that are stronger than the old porcelain and metal crowns, and are made from single blocks of ceramic-like materials.  They are made from lithium disilicate or Zirconia.  I know, you are really happy you know that now.  Maybe someday you can get a trivial pursuit question right from things you learned by reading this.  Although I don’t seem to remember a lot dental technology questions in Trivial Pursuit.

When we make crowns, or any full coverage fixed restoration, we do have to remove some healthy tooth structure.  But our materials are so strong and precise now, that it is almost always less than 1.5 mm of tooth.   Here is a link to a simple animated video to help visualize what I am describing:

These newer materials we use are very strong, and when done properly, can last a long time.  We often take digital scans now instead of using gooey impression material, and our lab uses 3D Printing, CAD?CAM, and mills to create very precise crowns for us.  Here is link for a video showing one of the crown types we use on a regular basis for back teeth.  Scroll to about 30 seconds into the video to see a hammer test showing how strong these new crowns really are.

So, you need a crown.  Just know that you are not alone, and that often times it was inevitable that at some point it was going to be necessary.  That day you had a big filling placed as a teenager started you down this road, and you probably couldn’t do much to prevent it.  Just know that the procedure it pretty simple, and the results will look and feel great.