A dental crown is a type of restoration commonly used for severely decayed or damaged teeth. After you have a dental crown placed, you can usually expect the tooth to stay healthy and sturdy for many years to come. However, you may also notice a dark line under the crown either right away or after several years. If this happens, it does not necessarily denote an issue. Keep reading to learn why it may a dark line may appear around your dental crown — and what to do about it if it does.