Can a tooth still rot under a crown?

A common misconception among patients is that once a tooth is completely encased in a dental crown, it becomes entirely immune to cavities and decay, but the reality is that a tooth can absolutely still rot underneath a crown. While the artificial crown material itself—whether made of porcelain, ceramic, gold, or metal alloy—cannot decay, the underlying natural tooth structure that remains protected inside the cap remains vulnerable to bacterial infiltration and acid erosion. Decay typically develops when microscopic gaps or microleakage occur at the marginal seal where the crown meets the gumline, allowing sugary fluids, microscopic food particles, and cavity-causing bacteria to seep beneath the restoration over time. If a patient neglects daily flossing, fails to maintain proper brushing habits, or experiences gum recession that exposes the vulnerable root surface beneath the margin, decay can quietly progress undetected until it reaches the inner pulp, eventually necessitating a root canal treatment or complete removal of the crown.