When does a crown make a better choice than a filling? -

Can a cavity be too big to fill? | What constitutes a big filling? | How crowns strengthen teeth.

Crowns vs. Fillings

One of the biggest differences between a dental filling and a crown is the level of protection the latter provides.

  • Crowns strengthen teeth. - One of the hallmarks of crown placement is the way it strengthens a tooth. This is due to the way it cups over and encases it.

    The crown literally acts as a splint that holds the tooth together. And that means, once one has been placed the tooth can withstand a greater level of chewing forces without risk of damage.

  • Dental fillings don't offer as much protection. - In comparison, placing a filling doesn't substantially increase the overall strength of its tooth. And, as we describe below, in some instances it can actually place a tooth at greater risk for breaking.

Related page: The risks and outcomes of not placing a crown.

Actually, you can't have a discussion about crown vs. fillings, without first describing the size of filling (or cavity) involved.

1) With small fillings, there's usually no concern.

A small cavity repaired by a small dental filling.

A small cavity repaired by a small dental filling.

The ideal situation for placing a filling is one where it's used to repair a relatively minor amount of tooth damage, such as a "small" cavity.

In these instances, even after the preparation (hole) for the filling has been drilled, the tooth remains relatively intact. And because of this, it can be expected that it will be able to withstand chewing forces well.

2) Large fillings may leave a tooth at risk.

In situations where a relatively larger amount of tooth structure has been lost, damaged or needs to be trimmed away when decay is removed, the picture may be different.

With these cases, the overall structural integrity of the tooth may be compromised, possibly significantly so.

An analogy.

The structural integrity issue we're discussing here is a little like what you find with an egg shell.

  • If you take a raw egg and you want to break it open, well it really takes a pretty firm rap. That's because an egg shell, as an intact unit, is a surprisingly strong object.
  • Now, in comparison, say you've broken the egg open and the two halves of the empty shell are lying on their sides. In this condition, it's a fairly simple feat to crush each piece flat.
  • That's because the shell's structural integrity has been compromised. It's no longer an intact unit that's capable of withstanding forces well.

And that's why teeth with big fillings can be fragile.

Teeth are somewhat the same, in the sense that once a large portion of a tooth is lost (because it has broken, decayed, or has been drilled away) it's simply no longer as sound.

A small cavity repaired by a small dental filling.

A big cavity repaired by a big dental filling.

The parts that remain can be fragile (thin, weakened, unsupported) and therefore at greater risk for fracture.

It's not about what can be done.

Yes, it's true that a filling can be placed for teeth in this condition. That's not really the issue here. The problem is that if a filling is placed, the strength of the tooth is not greatly enhanced.

A filling doesn't reinforce a tooth (like a crown does). And, in fact, all a filling does is occupy the space of the lost tooth structure. Any fragile or weakened tooth portions that remain are still at risk for breakage.

A tooth whose filling played a role in it cracking.

The filling creates a wedging effect that cracks to tooth.

Some fillings create a wedging effect that causes tooth fracture.

There's yet another concern that comes into play when making a decision about whether to place a dental crown or a comparatively large filling. It has to do with the potential (harmful) affect that the filling may have.

In contrast to a crown that cups over a tooth, a filling is placed within one (it relies on the tooth's remaining structure to anchor it). And due to this configuration, the filling has the potential to act as a wedge when chewing pressure is applied to it.

If the biting forces are great enough, or continually reoccurring, at some point this wedging action may cause the tooth to crack or fracture. (See animation.)

3) What constitutes a big dental filling? When should a crown be placed?

Well, of course, these are the big questions. And it's more or less what you're relying on your dentist to advise you about. It's their obligation and responsibility to provide you with information and options about how best to restore your teeth.

a) Here are some common guidelines.

  • At a minimum, any filling that's greater than about 1/3rd of the width of its tooth can be considered to be "large." In these cases, the benefit of placing a crown should be evaluated.
  • Some dentists are even more conservative in their opinion. They feel that if a filling is greater than about 1/3rd of the distance between the tooth's cusp tips, it should have a crown placed.

These are all "big" dental fillings.

Images of large dental fillings.

The arrows indicate the most fragile portions of the tooth.

b) Here are some examples of "large" fillings.

Take a look at the frames of our animation. Each one shows a dental filling that could be considered to be "big," and therefore the tooth a candidate for a dental crown.

In each picture, an arrow(s) points to that portion(s) of the tooth which would be expected to be most prone to cracking or breaking off.

4) Not all teeth with large fillings will be problematic.

Possibly by now you've already been to the mirror so you can judge the size of the dental fillings in your mouth. Did you see any "large" ones?

Now, ask yourself, how long have those big fillings been in place? What's your answer? Two years, five years, longer? If so, what's the deal? If teeth with large fillings are so weak, why haven't parts of your teeth already fractured off?

Even your dentist can't see the future.

Of course, the answer is that no dentist can know for certain which teeth will develop problems and which ones won't. No doubt, if your dentist could see into the future, they wouldn't be spending their time practicing dentistry.

Dentists do, however, both from their dental training and clinical experience, have an idea of which teeth are at greater risk for breaking than others. And they have an obligation to report this information to you.

They may be considering the safest choice.

Clearly not every tooth with a big filling will crack or break. Certainly many people get many years of service out of restorations like these. Additionally, not every tooth that does fracture will be especially problematic to repair.

But if your dentist feels strongly about placing a crown, what they may be trying to relate to you is that they believe by doing so they will create the most predictable, successful outcome for your tooth over the long run.



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