What causes dental crowns to fail?

Dental crowns can fail for several reasons, both related to the crown itself and the underlying tooth. The most common cause of failure is decay under the crown, when bacteria leak in through a gap at the margin where crown meets tooth due to poor fit, cement washout, or poor oral hygiene, causing cavity under crown. Another major cause is fracture or chipping of the crown, especially porcelain crowns that can crack from biting hard foods, teeth grinding, or trauma. Crowns can also become loose and fall off when cement weakens over time or when underlying tooth structure is insufficient to support it. Gum disease and bone loss can cause crown to fail by loosening the tooth. Root fracture of the underlying tooth, often from large fillings or root canal treated teeth becoming brittle, leads to failure. Wear and tear over time, typically 10 to 15 years, causes crown to wear down. Poor initial design, bite misalignment, or insufficient tooth preparation can cause premature failure. Teeth grinding or clenching at night puts excessive force on crowns. Finally, allergic reaction or gum irritation to metal in crown can cause failure. Good hygiene and regular checkups extend crown life.