Crown or Filling? How Your Dentist Decides
Last year you had a cavity and it took twenty minutes. This year you have another one and you’re being told you need a crown, two appointments, and a temporary in between.
Nothing arbitrary is happening. The decision comes down to one question: how much healthy tooth is left to work with.
A filling repairs a small-to-moderate area of decay and leaves most of the natural tooth in place. A crown caps the whole tooth, and is used when too little sound structure remains for a filling to hold reliably, or when the tooth is cracked, badly worn, or has had a root canal. How much healthy tooth is left decides which you need.
What is the difference between a crown and a filling?
A filling replaces a small-to-moderate area of lost tooth structure. Your dentist removes the decay and bonds tooth-coloured composite into the space. Most of the natural tooth stays where it is, and the repair relies on that remaining structure for strength.
A crown is a custom cap that covers the entire visible tooth. It’s used when too little sound structure remains for a filling to hold reliably, or when the tooth is cracked or weakened and needs full coverage to keep from breaking.
A filling fills a hole. A crown rebuilds and protects the whole tooth.
| Filling | Crown | |
|---|---|---|
| Repairs | A small-to-moderate area of decay or damage | The entire tooth, capped completely |
| Natural tooth | Most of it stays in place | Reshaped to accept the cap |
| Appointments | One | Two, about one to two weeks apart |
| Right when | Plenty of healthy structure surrounds the repair | The tooth is cracked, heavily broken down, or has had a root canal |
| Insurance category | Basic, around 70–80% | Major, around 50% |
| CDCP preauthorization | Not required | Required |
When is a filling enough?
A filling is the right call when:
- The decay or damage is small to moderate
- Plenty of healthy tooth surrounds the repair
- The tooth isn’t cracked or structurally compromised
- It’s an early cavity caught at a checkup
That last point is doing more work than it appears to. Decay caught at a routine exam is almost always still in filling territory. The same decay found eighteen months later, after it’s had time to spread toward the nerve, may not be. This is the practical argument for regular checkups, and it’s a more concrete one than “it’s good for you.”
When does a tooth need a crown?
A crown becomes the better option when:
- Decay or a previous large filling has taken a substantial portion of the tooth
- The tooth is cracked, fractured, or visibly worn down
- The tooth has had a root canal — especially a molar, which becomes brittle once the pulp is gone
- A filling has repeatedly failed in the same tooth
- The tooth needs full coverage to handle normal chewing force
In these situations a filling doesn’t fail because it was placed badly. It fails because there wasn’t enough tooth around it to support the load, and the remaining walls fracture under chewing pressure.
What if the tooth is borderline? Inlays and onlays
Plenty of teeth sit right on the line. A very large filling can work — but if it spans most of the biting surface, it can leave the surrounding walls thin and prone to cracking, and you’ve traded a smaller repair now for a bigger one later.
This is where an onlay comes in, and it’s underused in patient conversations. An onlay covers more of the tooth than a filling but less than a full crown, replacing one or more cusps while leaving healthy structure intact. It’s a genuine middle ground for a tooth that’s too damaged for a straightforward filling but not damaged enough to justify removing sound tooth structure for a full crown. Inlays and onlays are part of what we do here, and for the right tooth they’re often the more conservative choice.
What your dentist is weighing: how much healthy structure remains, where it is (the walls matter more than the top), how much chewing force the tooth handles, and whether you grind.
How long do crowns and fillings last?
It depends more on the tooth than on the restoration.
For crowns, the largest real-world dataset we have comes from roughly 1.2 million NHS crowns, which found 77% still in service at five years, 63% at ten years, and 53% at fifteen — a median of about sixteen years. Controlled studies of specific materials report better five-year figures — around 95% for metal-ceramic and 97% for lithium disilicate.
Both numbers are true and the gap between them is instructive. Crowns placed and monitored under study conditions do very well. Crowns in ordinary use, across every kind of patient and every kind of tooth, do respectably but not indefinitely. A crown is a long-lasting restoration, not a permanent one.
The variables that move the needle are your bite, whether you grind, and how well you clean around the margin at the gumline. A night guard for a grinder is a small, straightforward intervention that meaningfully extends the life of restorative work.
How does insurance treat crowns and fillings differently?
This surprises people more than the clinical side does.
Fillings are usually classified as a basic service and reimbursed around 70–80%. Crowns are usually a major service, reimbursed around 50%, and they draw much harder on your annual maximum.
Some plans also carry a downgrade clause that pays only the silver amalgam rate for a white composite filling, leaving you the difference. And under the Canada Dental Care Plan, fillings need no preauthorization while crowns do.
None of this should drive the clinical decision. But it’s a reason to ask for a predetermination before crown work, so your share is confirmed in writing before the tooth is prepared. We submit those routinely and direct-bill all insurance companies.
What happens if you wait?
Decay doesn’t stall and it doesn’t reverse. A cavity that needs a simple filling today can, left alone, reach the nerve and turn into a root canal plus a crown — a bigger procedure, more appointments, and a permanently weaker tooth.
The tooth that gets a filling this year and the tooth that needs a crown next year are frequently the same tooth.
Common questions
Is a crown always better than a filling? No. A crown is better only when the tooth needs full coverage. Where a filling will hold, it preserves more of your natural tooth, and preserved tooth structure is worth something.
Why did my dentist recommend a crown when I only have a small cavity? Usually because the visible cavity isn’t the whole story — an old large filling underneath, a crack, or decay that spread wider under the enamel than it looked from the surface. Ask to see the x-ray. It’s usually obvious once you’re looking at it.
Can a large filling turn into needing a crown later? Yes, and it’s common. A filling that spans most of a tooth leaves thin walls, and thin walls fracture. That’s the trade-off being weighed when a dentist recommends a crown for a tooth that a filling could technically still repair.
Does insurance cover both? Both, at different rates — fillings around 70–80% as a basic service, crowns around 50% as a major one. More on insurance.
What’s an onlay? A restoration that covers part of the biting surface, including one or more cusps, without capping the whole tooth. It sits between a filling and a crown and is a good fit for teeth in the grey area.
If you’ve been told you need a crown and you’d like a second opinion, or you just want the reasoning explained with the x-ray in front of you, call 604.457.2273. Mellow Family Dental Care, Unit 150–20528 Lougheed Highway, West Maple Ridge.
Sources: Burke FJT, Lucarotti PSK. Ten year outcome of crowns placed within the General Dental Services in England and Wales. British Dental Journal 2018;225:1011–1018. Link · Sailer I, et al. All-ceramic or metal-ceramic tooth-supported fixed dental prostheses? Dental Materials 2015;31(6):603–623. Link
This article is general information and does not replace an in-person dental exam. Which restoration suits your tooth depends on findings only a clinical exam and radiographs can establish.
