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The short answer: a filling repairs a crack when enough healthy tooth remains to hold it; a crown is needed when the crack has weakened the tooth's own walls.
Start with what the crack leaves behind. A composite filling works when the crack is small and the surrounding walls are thick enough to support it: the resin is placed in increments no thicker than 2 mm, each one cured under the lamp for 20–40 seconds, and the repair is finished in a single visit. On typical ranges it serves 5–10 years.
Amalgam is the longer-lived filling. The same single-visit logic applies, but the typical lifespan stretches to 10–15 years — roughly five years more than composite on the published ranges. Neither material, however, can stop a weakened cusp from flexing and eventually splitting under biting load.
On narrow screens, swipe or scroll the plate sideways.
That is the point where a crown enters. A porcelain-fused-to-metal crown lasts 5–15 years; a full zirconia crown lasts 10–20. The price of that protection is time: 60–90 minutes of preparation, then 2–3 weeks wearing a temporary crown while the laboratory makes the permanent one.
The deciding questions are mechanical. How deep does the crack run? How much sound enamel and dentine remain on each side of it? Does the tooth take the full force of the bite? A crack that stays shallow keeps the filling option open; a crack that undermines a cusp tips the decision to a crown.
If the crack has reached the pulp, the sequence changes entirely — root canal treatment first, crown second — which is laid out step by step on the root canal page. And the appointment where all of this is actually measured is the routine checkup, described minute by minute on the checkup timeline page.
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