Cosmetic Dentistry

Why Is There a Dark Line Around My Crown?

By Douglas Sandquist, DDS

Updated September 22, 2026

A dark line at the top of a crown, right where it meets the gum, is one of the most common things people point to when they smile in the mirror. On an older crown it’s almost always the same thing: the metal the crown was built on. Whether it’s worth doing anything about depends on which of two things you’re seeing, and on what the crown is made of.

Crowns used to be built like the old bathtubs

Think of the old footed bathtubs: cast iron underneath, with porcelain fused over the top. For decades most crowns were made the same way. A thin metal shell fits over the tooth, and porcelain is baked onto it. Dentists call it porcelain fused to metal. It’s strong, and plenty of these crowns have done their job for many years.

The catch is that the metal is always there. As long as it stays hidden, nobody notices. The dark line is what it looks like when it stops being hidden.

Two ways the metal shows

The collar itself. Many of these crowns have a thin band of metal right at the edge, where the crown meets the tooth. When the crown was new, that edge sat under the gum. It usually starts showing after some gum recession: the gum pulls back a little over the years, and the band that was tucked out of sight is now at the surface, as a gray or black line.

A shadow. Sometimes no metal is visible at all, and the gum edge still looks dark. That’s a shadow. A natural tooth lets light pass through it, and that light also illuminates the root just under the gum. Metal blocks it. With no light coming through the crown, the root behind it stays dark, and so does the gum line in front of it.

Either way, the cause is the same. It’s the metal.

What it looked like for one of our patients

C.J. had two old crowns on his upper front teeth. You can see the metal collars at the gum line in his before photo.

Before: C.J.'s smile, with the metal collars of two old front crowns showing as a dark band at the gum line — Before: the metal collars on his two front crowns show as a dark band at the gum.

We replaced them with all-ceramic crowns, which have no metal at all, so light passes through them the way it passes through a tooth. While we were at it, he decided to have six upper teeth and seven lower teeth done.

After: C.J.'s all-ceramic crowns, with no dark line at the gum — After: all-ceramic crowns, with no metal to show at the gum line.

See C.J.’s before and after in our gallery.

When a crown with no metal gets a dark line

All-ceramic crowns can show a black line too, but it means something different. There’s no metal to show through, so a dark line usually means there’s a problem with the seam, the margin where the crown and the tooth meet.

That’s worth having looked at, and it isn’t the same conversation as a metal collar. A metal collar showing is mostly about how it looks. A problem at the seam of a crown is about the crown and the tooth underneath it.

Not always a new crown

If it’s caught early and the area is small, sometimes a small composite repair can be done right at the edge of the crown instead. That’s case by case, and we’ll tell you at an exam whether yours is a candidate. For C.J., replacing the crowns with all-ceramic ones was the answer.

How to tell which one you have

Most people don’t know what their crowns are made of, especially if someone else placed them years ago. That’s fine. We can tell at an exam, and we’ll tell you which of these you’re looking at: a collar, a shadow, or a seam that needs attention.

A dark line on an old metal-based crown isn’t an emergency. Nobody has to replace a crown because of how the edge looks. But if it bothers you, it’s a perfectly good reason to ask, and if the crown has no metal in it, it’s a reason to get it checked.

Call 702-734-0776 or tell us what’s going on. More on how we make crowns, and on what wears out porcelain over time.

Common Questions

What is the dark line at the top of my crown?

On an older crown it’s almost always the metal the crown was built on. For decades most crowns were porcelain fused to metal, built like the old footed bathtubs: a metal shell with porcelain baked over it. The line is either the thin metal collar at the edge of the crown showing at the gum, or a shadow where the metal keeps light from passing through the crown and lighting up the root.

Why did the dark line show up years after I got the crown?

It usually shows up after some gum recession. When the crown was new, its metal edge sat under the gum. As the gum pulls back a little over the years, that edge ends up at the surface, where it shows as a gray or black line.

Why is my gum dark above a crown when I can’t see any metal?

That’s usually a shadow. A natural tooth lets light pass through it and illuminate the root just under the gum. The metal inside a porcelain-fused-to-metal crown blocks that light, so the root behind it stays dark, and the gum line in front of it looks gray.

Can all-ceramic crowns get a dark line?

Sometimes, but it means something different. All-ceramic crowns have no metal to show through, so a black line on one usually means there’s a problem with the seam, the margin where the crown and the tooth meet. That’s worth having looked at.

Is a dark line around my crown an emergency?

On an old metal-based crown, no. A metal collar showing is mostly about how it looks, and nobody has to replace a crown because of the edge alone. If the crown is all-ceramic and has developed a dark line, it’s worth getting checked, because that usually points to a problem at the seam.

How do you fix a dark line around a crown?

When it’s the metal, the usual fix is replacing the crown with an all-ceramic one, which has no metal at all and lets light pass through the way a natural tooth does. That’s what we did for C.J., whose case is in our smile gallery. If it’s caught early and the area is small, sometimes a small composite repair can be done at the edge of the crown instead. That’s case by case, and we’ll tell you at an exam which kind of line you have before recommending anything.