You look in the mirror, smile, and frown. There’s something off—a thin black line where your old dental crown meets your gumline. Is it an infection? Is it time to panic? A hundred questions go through your mind. But it’s okay—just breathe. The line you’re seeing usually isn’t a sign of anything serious. Keep reading to see what’s going on and learn how your dentist can fix it.
The Metal Underneath Is Showing Through
Many crowns, especially older ones, are made from porcelain fused to a metal base (PFM). This design combines the strength of metal with the natural appearance of porcelain on the visible surface.
Over time, your mouth undergoes many changes, and your gums could recede. This causes the edge at the base of the crown to become exposed, creating a thin strip of visible metal. This is ultimately what creates the dark line you see in the mirror.
Why Are My Gums Receding?
Gum recession is extremely common, and while it often becomes more noticeable with age, it usually has specific causes behind it, like:
- Brushing Too Hard: Aggressive brushing or using a stiff‑bristled toothbrush can physically wear away gum tissue over time.
- Gum Disease: Inflammation from plaque and tartar weakens the attachment between your gums and teeth, causing the tissue to pull back.
- Tooth Position: Teeth that sit slightly out of alignment or toward the outside of your arch often have thinner gum coverage, increasing the risk of recession.
- Clenching or Grinding: Excessive pressure on your teeth can strain the supporting tissues, weakening them.
Is Gum Recession a Problem?
It can be, depending on the severity. At the very least, cosmetically, many patients don’t love the look. Functionally, some slight gum recession won’t hurt, but it can be a sign of something more serious that may affect the health of your tooth. Gum recession, when ignored, can also affect your crown’s fit, so a checkup is generally warranted when you see the black line appear.
What Can Be Done About It
The most common fix is replacing the older crown with a newer, all-ceramic or all-porcelain restoration that doesn’t rely on a metal base—eliminating the dark line entirely. In some cases, addressing the underlying gum recession may also be part of the conversation. A consultation is the best way to find out which option makes sense for your smile.
If you’ve noticed this line on one of your own crowns, don’t ignore it. A quick trip to the dentist can put your mind at ease and help you decide if it’s time for an upgrade.
About the Author
Dr. Sheren Elsaid earned her dental degree from Temple University Kornberg School of Dentistry and completed an Advanced Education in General Dentistry residency with NYU Langone Dental Medicine. In 2025, she earned her Fellowship in the Academy of General Dentistry (FAGD)—a distinction held by less than 6% of dentists nationwide. At Zen Dental Care, Dr. Elsaid provides comprehensive crown restorations using modern, metal-free materials. Call (973) 370-5221 to schedule your consultation or visit our website here to explore other services.