A dental crown is a long-lasting solution to protect a compromised tooth, but it can also be used along with other procedures, like root canal therapy. They can last for many years with the correct care. However, over time, you may notice a dark line forming near your restoration where your crown meets your gum line. The blemish can be caused by many factors, like gum recession. Your dentist will determine what’s causing the imperfection and what can be done to improve its appearance.