Could my retainer be leaving a black line at the middle of two front teeth?

Yes, it's possible that your retainer could be leaving a black line at the middle of your two front teeth. Retainers are used to hold teeth in place after orthodontic treatment, and they are typically made of metal or plastic.

Over time, the metal in a retainer can cause discoloration of the teeth, especially if the retainer is not properly cleaned. The discoloration can appear as a black line at the gumline or between the teeth.

If you are concerned about the black line on your teeth, you should talk to your dentist. They can determine if the discoloration is caused by your retainer and recommend a solution. In most cases, the discoloration can be removed with a professional cleaning.