It is very common for people to think once they have a crown they never need it replaced. A crown is a full coverage “cap” that covers the tooth after a lot of breakdown or a root canal. The crown meets the tooth usually close to the level of the gum line, called a margin.
Anywhere around the margin is an area susceptible to a cavity. This is where plaque and bacteria collect. If it is not brushed off or removed, the acidity that is created breaks the tooth structure down and a cavity results.
If it is found early and in an area that your dentist can access, the cavity can be fixed easily with a filling.
If it is found late and between the teeth, the crown has to be removed, the decay removed, and a new crown made.
You could also have a bite that is not working for you. This can cause stress on the crown, causing it to break. Leaving a broken crown can cause food and bacteria to collect, creating a cavity, gum inflammation and/or periodontal disease.
It is important to have regular dental exams and X-rays when you have crowns. The dentist will check the margins for any decay or leakage and the X-rays for any signs of decay between the teeth.
That way you can catch things early before they hurt you or it becomes a more expensive problem.