What causes a black line near the crown edge on the gum line?

The aging process of the porcelain crowns causes the visible dark lines along the gum line. These dark lines commonly manifest in PFM crowns, porcelain fused-to-metal dental crowns, which incorporate tooth-colored porcelain on the exterior and metal for structural reinforcement underneath.

This dark line arises between the crowns and the roots of your teeth, stemming from the exposure of a minute amount of metal along this boundary.

PFM crowns also block the light going into the teeth and roots due to the metal substructure, so the teeth and roots become dark. A metal substructure can cause black lines to appear along the gum by blocking light entry.

Cosmetic dentists usually try to conceal this thin, dark line beneath the gum line. However, over time, gum recession will expose the dark line. The dark line may manifest through the gum tissue in certain instances, resulting in a darkened gum appearance.

You cannot cover the dark line with dental bonding or composites because these options don't bond to the crowns, and we do not have enough thickness to hide the black color. Dark lines will show through the gum no matter what.

black line around tooth base
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Removal of Dark Lines

Though primarily an aesthetic concern, the presence of the dark line does not indicate a significant issue with a crown's functionality. Nonetheless, suppose the black line is prominently visible on a front tooth. In this case, you might want to consider replacing the crown with alternative materials to achieve a more natural aesthetic.

The disadvantage of using metal is that not only will there be a black line around the edges, but the presence of metal will also prevent light from passing through, resulting in an opaque appearance similar to temporary teeth.

All porcelain crowns can let the light go through, which results in transparency and looks like natural teeth.

Causes for black/dark lines at the gum line

Multiple factors may contribute to the emergence of the black line at the base of a crown, with certain factors being more prevalent than others.

black lines around teeth
  • Crown Material:

    Dentists commonly use porcelain fused to metal (PFMs) to make traditional crowns. PFMs consist of porcelain over a metal base, which can show as a dark line near the gum line if the crown margin becomes visible due to gum recession.

  • Dark root due to the old root canal treatment:

    Trauma to the natural tooth may cause the underlying tooth structure to darken, either after a root canal treatment or independently.

  • Gum Recession:

    Aggressive brushing, teeth grinding, periodontal disease, or teeth shifting can cause gum recession.

    Gum recession can expose the crown margin, leading to the appearance of a dark line that is sometimes mistaken for decay.

  • Decay:

    Despite the added protection crowns provide, they are still susceptible to decay, especially around the margins.

    Some mistakenly believe that crowned teeth are immune to decay. Still, regular dental check-ups are necessary to ensure the integrity of the crown and effectiveness in protecting the natural tooth beneath it.

dark lines on teeth near gums
*Due to open margins and staining, the composite veneers were removed and replaced with porcelain veneers.

How To Get Rid of Dark Lines

The only solution to this aesthetic concern is replacing the dental crowns using the newer all-porcelain material with no metal understructure. When replacing a single dental crown at the front teeth area, anticipate the possibility of requiring multiple appointments before the new crown is permanently cemented. As the central incisors hold the utmost prominence in the mouth, achieving a seamless match presents the most significant aesthetic challenge.

Achieving a seamless match for one central incisor is one of the most challenging procedures.

Many dentists and patients ask to do two central teeth simultaneously for a better color match, even if the other central tooth is healthy. However, our facility excels in replicating one central tooth precisely by using special cameras and filters to see the actual color.

Contact us or call us at (281) 531.0710 for a free consultation

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Dr. Shimizu is an accredited member of the American Academy of Cosmetic Dentistry. There are 486 dental professionals worldwide (Only four in Houston) as of 2024 who have achieved this prestigious honor.