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

Can a cavity be too big to fill? Examples of large (risky) fillings. | How crowns strengthen teeth. | Situations where placing a filling makes a suitable, possibly preferred, choice.

Crowns vs. Fillings

You may find yourself in the situation where your tooth needs to be rebuilt. And your dentist says that either a dental crown or a filling might be placed. If so, the question that seems to run through many people's mind is:

  • Does choosing crown placement ... the repair that costs more (vs. a filling) ... and takes more appointment time (usually two visits vs. just one) ... really make the better choice?

As an aid in making this decision, this page outlines important differences between these two options, primarily from the standpoint of the health outlook for your tooth. It explains situations when choosing one rather than the other might result in a significant negative event, with fracture being a primary concern.

To get the full picture ...

Admittedly, there are other factors that you will want to consider.

And as alluded above, these include cost and simplicity of placement. There is also the issue of restoration longevity (crowns tend to last longer but a filling can provide reasonable service too, if placed for appropriate applications like discussed on this page).

For information about these additional topics, just follow the links above.


Choosing between dental crown and filling placement. - Factors to consider.

a) Does the tooth require strengthening?

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

  • Crowns strengthen teeth. - One of the hallmark characteristics of a dental crown is the way that it reinforces and strengthens a tooth. This is due to the way it cups over and encases it.

    The crown literally acts as a rigid splint that holds the tooth together. And that means that 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 a tooth. And as we explain below, in some cases choosing this option may actually place the tooth at greater risk for fracture.

    (Related page: Broken teeth - Repairs and outcomes.)

Of course, if your tooth doesn't really require strengthening, then placing a crown is overkill. And in fact, doing so makes a poor choice for your tooth.

Background -

Actually, you can't have a valid discussion about crowns vs. fillings, without first describing the size of the filling that's planned.

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

Animation show a small cavity repaired by placing a small dental filling.

For small repairs, placing a filling makes the right choice.

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 this situation, even after the preparation (hole) for the filling has been drilled, the tooth remains relatively whole and intact. And because it still retains the bulk of its structural integrity, it can be expected to still be able to withstand the chewing forces it's exposed to well.

With this situation, placing a filling (vs. a crown) is actually the superior choice.

In cases where only a minor amount of repair is needed, placing a crown instead of a filling can actually be detrimental to the tooth. That's because:

Of course, these events don't occur in all cases. But the potential for them is great enough that placing a crown isn't justifiable if a simpler type of restoration can satisfy the tooth's needs.

2) How larger fillings frequently leave a tooth at risk.

Animation shows how large filling placement may lead to tooth fracture.

Large dental fillings can leave a tooth vulnerable to fracture.

In situations where a relatively greater amount of tooth structure has been lost, damaged or needs to be trimmed away when decay is removed, the tooth's picture is likely different than above.

In these cases, the overall structural integrity of the tooth may have been compromised, possibly significantly so, and to the point where it is at risk of fracture.

An analogy.

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

  • If you take a raw egg and you want to break it open, it really takes a pretty firm rap. That's because an eggshell, 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 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.

How filling preparation size affects tooth strength.

Animation showing how restoration size affects tooth strength.

The numbers shown are the reduction in tooth stiffness (a measure of tooth strength).

That's why teeth with big fillings can be fragile.

A tooth is somewhat the same, in the sense that once its structural integrity has been altered (because it has broken, decayed, or has been drilled away) it's simply no longer as sound.

Research evidence.

This effect was documented in a study by Reeh. It evaluated the stiffness of premolars (a measure of tooth strength) after cavity preparations (holes) for various size fillings had been drilled.

Just as you might expect, larger-sized preparations resulted in greater loss of tooth stiffness.

Our animation illustrates the amount of stiffness reduction associated with the standard outline form of the different classifications of fillings evaluated by the study.

  • 1 surface cavity preparation = -20%
    2 surface = -46%
    3 surface = -63%

This paper stated that this same general trend could be expected for molars too.

Section references - Reeh

Animation illustrating how the presence of an existing filling may lead to tooth fracture.

A filling may create a wedging effect that ultimately cracks its tooth.

b) Fillings can create a wedging effect that leads to tooth fracture.

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

A major difference between crowns and fillings.

In contrast to a dental crown that cups over and encases the tooth it's placed on, a filling is embedded within it.

And due to this positioning, it has the potential to act as a wedge between opposing tooth sides when chewing pressure is applied to it. And if the biting forces are great enough (which would be the case with comparatively larger fillings where the walls of the tooth are comparatively thinner), or small but perpetually recurring, at some point this wedging action may cause the tooth to crack or fracture. (See animation.)

Section references - Rosenstiel

This effect can take place with either large or small fillings. But as discussed above, those teeth that have comparatively larger restorations may already be at comparatively higher risk of fracture, and therefore this issue of greater concern with them.

c) The question isn't only "if" a filling can be placed.

Don't confuse the issue of "can a filling be placed" vs. "should one be."

Dentists are humans just like anyone else. And sometimes an aspect of the treatment options they offer has to do with trying to satisfy their patient's wishes (with cost issues often being the primary factor when crowns are involved).

Know what you're getting.

Just because they feel they can anchor some type of filling to replace your tooth's missing parts, you still need to ask them what they expect the results to be.

Should the restoration be considered to be a "permanent" fix? Or instead, just an interim solution, with a crown hopefully placed before any further harm occurs?

Even the latter approach doesn't necessarily make a bad plan. But if that's the situation, you should be fully aware of it.


What constitutes a 'big' dental filling? When should a crown be placed instead?

As mentioned above, and discussed further below, a big part of determining when a crown is indicated for a tooth instead of a filling has to do with the size the filling would need to have.

That's because when larger amounts of tooth structure are missing, the tooth is typically in greater need of reinforcement (a function that crowns, as opposed to fillings, excel in providing).

Of course, deciding when a filling seems "too big" (to provide needed strength or predictable service) is really only something your dentist's evaluation can determine. During this process, here are some of the issues they will consider.

Intercuspal distance = Cusp tip to cusp tip.

Graphic relating maximum filling size to tooth intercuspal distance.

Fillings greater than 1/3 the distance between cusp tips tends to significantly weaken a tooth.

Crowns vs. fillings - Common guidelines.

As you would hope, the general rules of thumb that a dentist follows come from (or are at least confirmed by) research.

  • A study by Larson determined that fillings that take up just 1/3rd of the "intercuspal distance" of a tooth (see picture) reduce the tooth's resistance to fracture by more than one half.
  • Geurtsen stated that a tooth's risk for fracture increased substantially as its filling approached 50% of its intercuspal distance. This paper's recommendation was that fillings, composites (white) or amalgam (silver), should not exceed 1/3 to 1/4 this distance.
Your mileage may vary.

Not all dentists are as conservative with their recommendations as suggested by the guidelines above. And from a practical standpoint, many teeth with "larger" fillings do just fine, even over the long term. (A quick look in your mouth may confirm this.)

But at least from a standpoint of research findings, there is reason to expect that there is some level of risk involved with taking this approach.

Section references - Larson, Geurtsen

These are all "big" dental fillings.

Slideshow of images of large dental fillings.

The arrows indicate the most fragile portions of the tooth.

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.

Generally speaking, they're the cusp that the filling encroaches on the most. (Cusps that don't meet the requirements stated in the general rules above.)

 

Not all teeth with large fillings are 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 yours already fractured off? Don't these teeth need dental crowns, immediately?

 

What do experts say?

We found a section in the dental treatment planning textbook authored by Stefanac that discusses this type of scenario at length.

It goes as far as to state that diagnosing the need of a dental crown for a tooth that has a large filling that has provided acceptable service for some years and has no obvious deficiencies "is one of the most common opportunities for overtreatment in dentistry."

When should replacement be considered?

The book suggests that basic reasons for intervening include: a defect in the filling, the identification of tooth decay or a fracture line in the tooth, and pain on biting. And states that short of the presence of one or more of these symptoms, making a compelling case for crown placement can be difficult.

Of course as it should, the book expounds on more detailed scenarios and considerations that could be factors that tip the scale in favor of one treatment approach over the other. But the salient point we took away was that the act of crown placement can have unintended consequences, and as such a decision to place one must be based on a reasonable justification.

(We'll also state that we noticed that there's an added implication here that large fillings (at least those that survive an initial number of years) can make a reasonable choice for teeth.)

What to do?

Obviously, with this subject there are no cut and dried answers. The hope is, base on both their knowledge and clinical experience, that your dentist has the ability to formulate an educated opinion about which of your teeth have a true need for a crown.

And if so, they should be able to make their case relatively easily. But if your dentist's recommendations for crown placement instead seem more of the blanket variety (with every tooth that has a filling needing one, or every problem solved by one), they may not be the level of clinician that you imagined.

Section references - Stefanac


Don't overlook that prevention is really the key.

As this page has discussed, in many, many cases the debate between placing a filling or a crown simply boils down to how much tooth structure has been lost. And that suggests that a person's potential for requiring a crown can be reduced if steps are taken to help to keep tooth damage to a minimum.

Of course, in many cases you'll have no control over this factor at all. But there actually are some habits and lifestyle choices that do increase a person's risk for tooth damage, and therefore crown placement. If you'd like to learn more, read this page: 8 steps that can reduce your chances of ever needing a dental crown.

 
 
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