Quick answer
A filling repairs a tooth that is still mostly tooth: it patches a cavity or chip within strong surrounding walls. A crown protects a tooth that is mostly repair: when old fillings, cracks or root canal treatment have left walls too thin to survive chewing forces, a crown wraps the whole tooth and holds it together. Re-filling an over-filled tooth repeatedly is the false economy; each round removes more tooth until a crack takes the decision away. An honest recommendation explains which side of the line your tooth sits on and why.
The structural logic, plainly
Teeth survive chewing because their walls brace each other like a barrel's staves. A filling replaces the middle; the walls do the work. Each re-filling widens the middle and thins the walls, until eventually the tooth is a thin porcelain cup of enamel around a large patch, and biting forces flex it. Flexing walls crack, and cracks under fillings are how molars die suddenly on a Tuesday.
When a filling is the right call
- New decay or chips in a tooth with strong, thick remaining walls
- Replacing one failed filling of reasonable size
- Small repairs where most of the natural tooth still carries the load
When a crown earns its cost
- Cusps (corners) broken off, or a filling occupying most of the tooth's width
- Visible crack lines, or the classic bite-release pain of a cracked tooth
- After root canal treatment on back teeth, where the tooth is brittle and unprotected chewing is a gamble
- The third-or-fourth-filling conversation: continuing to patch is possible, but each round is bigger and the endpoint is predictable
Questions worth asking anyone, including us
How much natural wall remains? What happens if we fill it again instead? What's this tooth's realistic future either way? A practice comfortable with those questions is quoting the tooth, not the price list; every Align recommendation comes written, with the reasoning attached.