Black line at gumline
This Chicago Northshore resident complained as a new patient that her recently done crowns did not match her natural teeth nor each other. The floss would shred when used around her dentistry and the gums would bleed. Knowing that bleeding is not normal, she felt that her dentistry did not fit well. Her gums were receeding from around the crowns one year after placement. Some of her new crowns had black lines at the gumline. She dreamed of having a pretty white smile and wanted her dentistry to be easy to clean.
Customized Empress Porcelain Selection
The patient elected to have new dentistry (veneers, crowns or bridges) done to replace or cover over and reshape all of her upper teeth. Our patients have the opportunity to decide how they want their porcelain to look. This patient wanted a bright and white look with less variation in color going from the gum to the edges of her teeth. Translucency in natural teeth often is what creates this variation. These restorations were done without translucency at the patient's request.
Black Gum Line around crown: Edge of crown is dark
Nothing is more unsightly than dark areas visible at the base or margins of your dental crowns. This is especially true if you have a big smile and the dark lines show up in pictures. Dr. James Fondriest explains the mystery behind the black line and explain how you can avoid this issue.
What Causes a Black Line at the Crown Margin?
A dark gray or black ring around base of crown is possible whenever metal is used as a substructure for the crown. Porcelain-fused-to-metal – or PFM crowns have an opaque metal alloy substructure (often called the coping) that seals the tooth and offers support for the ceramic that is stacked and baked on top.
Metal with a low gold content is dark gray and is easily seen if not covered. Even 14-karat gold alloys have a gray color. PFM crowns can be beautifully crafted by a skilled dentist-technician team. Even still, it is much more difficult to keep this type of restoration looking good long-term. Metal gives the crown strength, while the porcelain on top gives it an aesthetically pleasing look.
Gray or black at the gum line can be present if the border (or margin) of the crown is exposed. All-porcelain crowns made with high translucency are more difficult to fabricate, but they do not have any metal, and are therefore often chosen as the most aesthetic option.
Fix Dark Lines at the crown margin with a porcelain butt joint margin
The average PFM crown will have metal at its border. The porcelain does not cover the margin. A higher quality dentist will pay extra for the dental technician (who actually makes the crown) to cut back the metal margin and bake a special “margin porcelain” to seal the crown. This is called a “porcelain butt joint margin”, and Dr. Fondriest routinely requests this feature when communicating with our dental lab. As a result, the gray metal is not visible at the gum line.
Can High-Quality Crowns Have Dark Gum Lines?
Yes, but not often and it shouldn’t happen for many years. There are four possible scenarios, which we will explore below.
Opacity of metal blocks the light
Teeth are surprisingly translucent. When light hits part of a tooth, the light is bounced around within the entire structure, including the root. The gum is actually illuminated by the lightened root and will appear a lighter shade of pink. If one of the teeth in your smile has a PFM crown (still the most commonly done type of crown), the opaque metallic coping will prevent light from going up the root. The gum (not the crown) will appear darker. A porcelain butt joint margin allows more light in the root but there is still less light going down the root.
Flexure at margin will break the seal
When a patient grinds his or her teeth, large lateral forces are exerted, causing flexure of the teeth. When there is a crown on a tooth, the flexure point will be at the crown margin. Over time, the cement used to seal the margins will slowly break down and begin to leak. Even with the highest quality crowns with porcelain butt margins, if there is leakage, there will eventually be staining.
No contact lens effect
Translucent porcelain can assume a contact lens effect at the margin. This makes margins virtually invisible; even with gum recession. Some types of well-made porcelain crowns can have a darkness at the gum line. This can occur if the crowns were originally made to make the teeth brighter for cosmetic reasons. Porcelain crowns and veneers that are used to brighten the teeth are created using more opaque porcelain to mask the dark tooth below. Opaque porcelain margins do not have a contact lens blending effect and will be visible after gum recession occurs.
Gum Disease or Gum recession exposes the margin
It takes more effort but dentists can tuck the margin of a crown beneath the gum line. This will hide the visual interface between the crown and the tooth root. As we age, our gums can recede. Good oral hygiene may not stop gum recession. In fact, gum tissue recession can affect even the most diligent patients. Five to 20 years after the crown is placed, gum recession may expose the margin. Planning for the future, the margin of the crown is stained by the lab technician to match an assumed shade of the root that the dentist cannot see. Often the optical properties of the crown and root are mismatched.
To learn more, contact us at 847-234-0517.