Why do crowns fall out?

Crowns can come out for a number of reasons. The teeth holding them can decay and break. The cement holding them can wash out and that can also cause a crown to become loose.

Some crowns fall out because the prepared tooth that holds is not retentive enough . Preparations that are too short or too tapered , often are not sufficiently retentive to permanently hold crowns, even when the crowns fit and the cement doesn't wash out.