Teeth turn black for a range of reasons, from surface stains caused by food and tobacco to deeper problems like decay, injury, or medication side effects. Some causes are purely cosmetic and easy to reverse, while others signal damage that needs treatment. Understanding the difference helps you figure out what you’re dealing with.
Surface Stains From Food, Drinks, and Tobacco
The most common cause of dark or black discoloration is extrinsic staining, meaning pigments that collect on the outer surface of your teeth rather than inside the tooth itself. Your teeth are coated in a thin protein film called the pellicle, and colored compounds from what you eat, drink, or smoke get trapped in that film over time.
Coffee, tea, red wine, and dark berries are frequent culprits. Tobacco is one of the worst offenders, whether smoked or chewed, because tar and nicotine bond aggressively to enamel and build up in layers that range from brown to true black. These stains tend to appear gradually and affect multiple teeth, especially along the gum line and between teeth where brushing misses. Professional cleaning or whitening can usually remove them, though they’ll return if the habit continues.
Tooth Decay and Cavities
A black spot on a single tooth, especially one that feels rough or soft to your tongue, is often a cavity. When bacteria break down enamel and reach the softer layer underneath, the damaged area traps food debris, bacteria, and breakdown products that darken over time. Early cavities may look like small dark dots. More advanced decay can turn a large portion of the tooth dark brown or black, sometimes with a visible hole.
Not every dark spot is an active cavity, though. Some teeth develop “arrested” decay, where a spot darkened at some point but the decay process stopped. These spots feel hard and smooth rather than sticky. A dentist can tell the difference with a visual exam and X-rays. Active cavities need filling or other restoration. Arrested ones are typically monitored without treatment.
Dead or Injured Teeth
A tooth that turns dark grey or black after a blow to the face, a fall, or even heavy orthodontic force is likely dying or already dead. The nerve and blood vessels inside the tooth (the pulp) bleed internally when damaged. Red blood cells break down and release pigments that seep into the tiny tubes running through the tooth’s inner layer. Over time, those pigments oxidize and darken, much like a bruise changing color under the skin.
The discoloration doesn’t always show up right away. In one documented case involving orthodontic treatment, the tooth didn’t visibly darken until about 10 months after the force was applied. The longer the dead tissue sits inside the tooth, the darker the staining becomes. A tooth in this state usually needs a root canal to remove the dead pulp, followed by internal bleaching or a crown to restore its appearance.
Iron Supplements
Liquid iron drops and syrups, commonly given to infants and young children for anemia, are a well-known cause of black tooth staining. The iron ions react with hydrogen sulfide produced by mouth bacteria, forming an insoluble dark compound called ferric sulfide that deposits on the enamel surface. The staining is especially obvious on teeth that have weak or underdeveloped enamel, which is common in baby teeth.
This type of stain sits on the surface and doesn’t damage the tooth itself. It can usually be polished off at a dental cleaning, though it tends to come back as long as the supplements continue. Giving the drops toward the back of the mouth, brushing soon after, or using a straw for older children can reduce buildup.
Chlorhexidine Mouthwash
Prescription-strength chlorhexidine mouthwash, often recommended after gum surgery or for stubborn gum disease, causes brown-to-black staining in some users. The staining isn’t caused by the mouthwash alone. It happens when chlorhexidine interacts with color-producing compounds in food and drinks. Aldehydes and ketones naturally present in many foods react with the chlorhexidine molecules already bound to your teeth, producing dark pigments on the enamel surface.
The staining is more likely on teeth that already have plaque buildup, and it intensifies with longer use. In clinical testing, the darkest category of stain (dark brown to black) appeared on less than 1% of tooth surfaces after 25 days of use. The discoloration is cosmetic and reversible with professional cleaning, but it’s a major reason dentists limit chlorhexidine rinses to short courses.
Silver Diamine Fluoride Treatments
Silver diamine fluoride (SDF) is a liquid applied to cavities, especially in young children or patients who can’t tolerate drilling, to stop decay from progressing. It works well for that purpose, but it has a dramatic cosmetic side effect: it turns treated tooth surfaces black, often within two minutes of application. The ionic silver in the solution oxidizes rapidly into metallic silver and silver oxide, which combine with proteins and minerals in the tooth to form dark compounds like silver phosphate and silver sulfide.
The staining is permanent on the treated area and intensifies with repeated applications. It only affects the decayed or demineralized parts of the tooth, so healthy enamel nearby stays its normal color. This selective staining is actually useful as a visual marker of where decay existed, but it’s also the primary reason many parents hesitate to accept SDF treatment for their children’s teeth.
Old Amalgam Fillings
Silver amalgam fillings, the metallic kind that were standard for decades, darken over time through oxidation, the same chemical process that tarnishes silverware. The metal mixture corrodes slowly inside the tooth, and dark oxidation products can seep into the surrounding tooth structure, giving the entire tooth a grey or blackish tint that shows through the enamel. This is especially noticeable on front teeth or thinner areas of enamel.
The discoloration is cosmetic rather than harmful in most cases, but it can’t be reversed by whitening because the pigment is embedded within the tooth itself. Replacing the old amalgam with a tooth-colored composite filling and sometimes adding a crown is the only way to restore the tooth’s natural appearance.
Black Line Stain in Children
Some children develop a thin black line that follows the gum line on several teeth, even with good brushing habits. This is called chromogenic black stain, and it’s caused by specific pigment-producing bacteria in the mouth, primarily species of actinomyces and prevotella melaninogenica. These bacteria produce dark sulfide compounds, likely iron sulfide, that deposit in a narrow band along the edge of the gums.
The stain is harmless and doesn’t indicate poor hygiene. In fact, some research suggests children with this type of staining may actually have lower cavity rates, possibly because the bacterial mix in their mouth is less favorable to the species that cause decay. The stain can be removed with professional polishing but typically returns within a few weeks or months. Most children outgrow it as their oral bacteria shift during adolescence.