I recently removed a tooth with a gold crown which was fitted in Berlin in 1946. The crown looked like it was made yesterday but the tooth had failed due to gum disease. Usually it is not the crown which fails but the tooth underneath it. I try to ensure that the fit of my crowns is perfect. This means that with good oral hygiene and a low sugar diet, the crown may last a lifetime.
Of course crowns are not indestructible and they are subject to wear and tear. Some people put their teeth through a lot more than others in terms of what and how they eat. Some people rigorously grind their teeth (bruxism). It is important that we establish the existence of these habits and try to correct them.