Why do I need a crown and not just a filling?
The short answer
A filling replaces a missing piece of the tooth. A crown covers the whole tooth, like a helmet. When a small part of the tooth is gone, a filling is usually enough. When a big part is gone, especially a chewing corner, the walls left behind can be too thin to hold up, and a crown protects them.
When a filling is often enough
- The cavity or old filling is small to medium.
- The tooth's chewing corners (cusps) are still thick and healthy.
- There's no crack, and you don't grind heavily.
Choosing a filling now doesn't rule out a crown later if the tooth needs one.
When a crown makes more sense
- A large part of the tooth is gone from decay, a break, or a big old filling.
- One or more chewing corners are broken off or undermined, with thin walls left.
- The tooth has a crack. See Why do I need a crown?
- It's a back tooth that's had a root canal. See Do I need a crown after a root canal?
- You grind your teeth. Grinding puts extra force on large fillings.
The in-between option: an onlay
An onlay (sometimes called a partial crown) covers only the weak chewing corners, while a crown wraps around the whole tooth.
- The big advantage: it's more conservative, so more of your healthy tooth is kept.
- The trade-offs: onlays are more technique-sensitive, meaning they're more demanding to place well. If one fails, the tooth will likely need a crown anyway.
- Insurance: most plans treat an onlay much like a crown, with the same criteria.
Why dentists can reasonably disagree
There's no single line where a filling stops being enough. Dentists weigh how much tooth is left, where it is, how hard you bite, and what they see in person, such as cracks that don't show up on an X-ray.
Questions to ask
- How much healthy tooth is left?
- Is a chewing corner broken or weak?
- Would a large filling or an onlay be reasonable for this tooth? What are the trade-offs?
- Do you see signs that I grind my teeth?
- If I choose a filling, what signs would tell us it's time for a crown?
- Before we schedule, can I get my cost in writing? (A predetermination if I'm using insurance, or a good faith estimate if I'm paying myself.)
When a second opinion makes sense
Reasonable if a crown is recommended on a tooth with little decay or only a small filling, and nothing is broken or cracked.