If you have gotten a dental crown in the past, you might’ve gotten good use out of it during the years. It has helped you bite more comfortably, but what if you started to notice a thin, black line forming around it? You might feel self-conscious about it, but it’s a common issue that can happen with porcelain-fused-to-metal (PFM) restorations. Here’s why it might’ve developed and what you can do to fix it.