Comparing the two
Filling or crown?
A filling replaces the part of a tooth that has been lost to decay or a break, and it works well while there is plenty of sound tooth around it. A crown covers the whole tooth and holds it together, which is what a heavily broken or heavily filled tooth needs. The deciding question is how much sound tooth is left, not how big the hole looks.
One fills a hole. The other holds a tooth together.
This is the comparison people are most often asked to make while sitting in the chair with a numb face, which is the worst possible moment for it. It is worth understanding beforehand, because the two treatments do genuinely different jobs.
A filling goes inside the tooth. Decay is removed, the space is cleaned and sealed, and the walls of the tooth around it carry on doing the work of chewing. While those walls are thick and sound, that arrangement is strong and it lasts.
A crown goes over the tooth. The tooth is shaped all round and a cover is bonded permanently on top, so the forces of chewing are carried by the cover instead of by walls that can no longer take them. That is the whole point of it, and it is why a crown is not simply a large filling made of something fancier.
How do they compare?
| Filling | Crown | |
|---|---|---|
| What it does | Fills the hole left where decay or a break is removed | Covers the whole tooth and holds it together |
| How much tooth is involved | Only the damaged part | The tooth is shaped all round to make room for the cover |
| Appointments | One | Usually two, with a temporary in between |
| Best when | There is plenty of sound tooth left around the damage | The walls of the tooth are too weak to hold themselves together |
| What it does for strength | Little. A large filling can act like a wedge | A great deal. It stops the tooth splitting |
| If it fails | Usually replaceable, sometimes with a bigger filling | Usually remade, and there is less tooth left to work with |
| Reversible | The tooth can still be crowned later | No. Tooth removed for a crown does not come back |
When does a filling stop being enough?
There is a moment where a tooth crosses from one treatment to the other, and it is easier to describe than to see from the outside. It is when the filling stops being held by the tooth and the tooth starts being held by the filling.
- How much wall is left. Thin walls, particularly between the cusps, are the main signal. They flex under chewing, and flexing is what eventually cracks them.
- Whether there is already a crack. A tooth that twinges on release when you bite something hard is telling you something a photograph will not.
- How many times it has been done. Each replacement takes a little more tooth. A filling being redone for the third time is usually a different conversation from the first.
- Whether you grind. Grinding shortens the life of both, and a heavily restored tooth in a grinding mouth is a tooth on borrowed time. A splint often belongs in the plan alongside whichever you choose.
- Whether the nerve is involved. A tooth that has had root canal treatment has usually lost a lot of structure, which is why crowns are common on back teeth afterwards.
What should you ask before you agree?
If a crown has been recommended and you were expecting a filling, there is one question that gets you a real answer: what specifically happens to this tooth if I have a filling instead? A dentist who has looked properly can tell you, in terms of that tooth rather than in general.
The follow-up worth asking is whether an onlay would do. It covers less of the tooth than a crown, it can be used where enough sound structure remains, and it removes less. Not every tooth is a candidate, and it is a fair question on any tooth where full coverage has been proposed.
There is no right answer that applies to every tooth. What there should be is a reason, specific to yours, from principal dentist Dr Fatima Kurnaz or one of our dentists, before anything is started and before you are numb.
Other questions people ask
Why can I not just have another filling?
Sometimes you can, and you should ask. The point where it stops being sensible is when there is more filling than tooth. A filling sits inside the tooth and the remaining walls hold everything together, so once those walls are thin, chewing forces work like a wedge and the tooth eventually splits. A split below the gum usually means losing the tooth.
Is a crown just the expensive option?
It is the more expensive option, and that is not the same thing. The question to ask is what happens if you choose the filling: if the honest answer is that it will probably be fine, take the filling. If the answer is that the tooth is likely to break in the next year or two, the cheaper treatment is the one that costs you a tooth.
What is an onlay?
Something in between. It covers part of the tooth rather than all of it, and it can be used where there is enough sound tooth left to support it. It removes less than a crown does. It is worth asking whether your tooth is a candidate before agreeing to full coverage.
Do I need a crown after root canal treatment?
Often on a back tooth, and often not on a front one. A back tooth that has had root canal treatment has usually lost a lot of structure and takes heavy chewing forces, and the Better Health Channel describes crowns as common afterwards for that reason. If one is recommended, ask why for that particular tooth.
Can I wait and see?
For a small filling in a tooth that does not hurt, sometimes, and it should be monitored rather than forgotten. For a tooth that is already cracking, waiting is a bet that it breaks in a convenient way, and it usually does not. Ask what specifically is likely to happen if you wait six months, and how that changes the treatment.
Which lasts longer?
A crown generally protects a weakened tooth for longer than a large filling does, but longevity depends on the tooth, your bite, whether you grind and how well it is cleaned around, far more than on the material. Anyone quoting you a number of years for either has not accounted for any of that.
Will it hurt?
Neither should. Both are done under local anaesthetic and the tooth is numb before anything starts. A deep filling can leave a tooth sensitive for a few weeks while it settles, and a crowned tooth can be tender to bite on for a short time after it is fitted. Tell us if either goes on longer than that.