Seeing a dark line or black tissue around a dental crown is common for people with dental restorations. This discoloration occurs at the junction where the crown meets the gum tissue. The cause can range from a simple cosmetic issue related to the crown’s material to a more significant underlying oral health concern. Understanding the source is the first step toward addressing it and restoring the appearance and health of your smile.
The Role of Metal Crown Materials
The most frequent reason for a dark line at the gum line is the presence of a Porcelain Fused to Metal (PFM) crown. PFM crowns were standard for many years, using a metal core for strength and a porcelain layer for aesthetics. The metal substructure provides the necessary durability to withstand the forces of chewing.
This metal substructure, often a silver or gold alloy, extends to the crown’s edge, or margin. When initially placed, this metal margin is hidden beneath the gum tissue. However, gum tissue naturally recedes over time due to age or aggressive brushing, exposing the opaque metal collar. The exposed metal then becomes visible as a dark or black line where the crown meets the gum.
A visual effect called “shadowing” also contributes to the dark appearance. The opaque metal core blocks light from passing through, unlike a natural tooth root. This lack of light transmission casts a dark shadow onto the surrounding gum tissue, making the area appear darker or grayish. Modern alternatives, such as all-ceramic or zirconia crowns, eliminate this issue because they contain no metal substructure.
Discoloration Caused by Gum and Tooth Health Issues
Discoloration not caused by the crown’s material may indicate an underlying health issue affecting the surrounding tissues or the tooth beneath the crown.
Amalgam Tattooing
One cause is amalgam tattooing, which appears as a permanent, bluish-black or gray spot on the gum tissue. This happens when tiny particles from old silver fillings become embedded in the gum during procedures like crown preparation. The embedded metal particles are inert and harmless, but they create a cosmetic blemish.
Recurrent Decay
A more concerning cause is recurrent decay developing beneath the crown’s margin. A small gap at the junction between the crown and the natural tooth allows bacteria to seep in. This decay progresses silently, and the deteriorating tooth structure begins to darken. The resulting dark shadow near the gum line signals that the tooth beneath the restoration is actively decaying.
Chronic Inflammation
A crown with a poor fit or improper margin seal can lead to chronic gum inflammation (gingivitis). An ill-fitting crown traps plaque and debris, irritating the gingival tissue. This inflammation can cause the gum tissue to appear a darker, bluish-red color, contributing to the perception of a dark line.
How a Dentist Diagnoses the Cause
A dental professional must conduct a thorough examination to accurately determine the source of the dark gum line, as the correct treatment depends on the underlying cause. The diagnostic process begins with a detailed visual inspection. The dentist assesses the color, texture, and exact location of the discoloration, noting whether the dark line is localized or uniform around the entire crown.
The dentist also uses a dental probe to check for gum recession and the health of the tissue surrounding the crown. Probing measures the depth of the gingival pocket and reveals if the crown margin is exposed or if swelling or bleeding indicates inflammation.
X-rays are an indispensable diagnostic tool, allowing the clinician to see beneath the crown and gum line. A radiograph can confirm the presence of metal particles (amalgam tattoo) or, more importantly, reveal radiolucent areas indicative of decay beneath the crown or a significant gap at the crown margin.
Treatment Options for a Dark Gum Line
Treatment for the dark line is directly guided by the diagnostic findings.
If the cause is purely cosmetic, such as the exposure of a PFM crown’s metal substructure due to gum recession, the primary solution is crown replacement. The old PFM crown is removed and replaced with an all-ceramic or zirconia crown, which eliminates the dark metal margin and shadowing. Gum grafting procedures may also be considered to cover the exposed margin and restore the gum line.
When recurrent decay is identified beneath the crown, the crown must be removed immediately to access and treat the affected tooth structure. The decay is cleaned out, the tooth is repaired, and a new crown is fabricated and placed to ensure a bacteria-sealing fit. If the decay is extensive and reaches the nerve, a root canal procedure may be necessary before the new crown placement.
For discoloration caused by a poorly fitting crown, the solution involves adjusting the existing crown to achieve a better margin seal or replacing it entirely to eliminate the plaque trap and resolve chronic inflammation. An amalgam tattoo typically requires no treatment as it is a benign condition. If the patient desires removal for aesthetic reasons, the spot can be addressed with minor surgical excision or laser therapy.