The appearance of a black tooth is a symptom of several distinct underlying causes, prompting concern about oral health. The reasons range widely, from superficial stains to serious structural issues or active disease processes. Determining the source of the black color requires a professional dental examination. A dentist must identify whether the issue is extrinsic (on the outer surface) or intrinsic (originating inside the tooth structure) to ensure correct treatment.
Black Staining Caused by External Factors
Black discoloration on the outer surface of the tooth enamel is referred to as extrinsic staining. These stains adhere to the acquired pellicle, a thin film of protein that forms on the tooth surface. The most common source of true black staining is dental plaque containing chromogenic bacteria, such as Actinomyces species. These bacteria react with iron in saliva or gingival fluid to form insoluble ferric sulfide, a black precipitate that deposits along the gumline in a characteristic dotted or linear pattern.
Other external factors also contribute to dark surface stains that may appear black or dark brown. Frequent consumption of dark-colored beverages like coffee, tea, and red wine leaves behind chromogens that bind to the enamel. Liquid medications, particularly those containing iron supplements or the antimicrobial mouthwash chlorhexidine, can also lead to dark discoloration. These extrinsic stains are superficial and do not indicate tooth decay; they can be removed completely through professional scaling and polishing procedures.
Structural Changes Within the Tooth
When a tooth darkens from the inside, the discoloration is considered intrinsic, arising from changes deep within the dentin or pulp chamber. One frequent cause is pulp necrosis, commonly known as a “dead nerve,” which often follows a dental injury or deep decay. After the trauma, the blood supply to the pulp dies, and the internal tissues decompose.
The breakdown of blood and tissue releases protein degradation products that penetrate the surrounding dentinal tubules, staining the tooth a dark gray or black color. Another intrinsic source is the presence of old dental materials, such as silver amalgam fillings. Metallic ions from the amalgam can leach into the adjacent dentin over many years, causing a dark, shadow-like discoloration visible through the enamel. In cases of trauma where the pulp bleeds internally, the iron released from broken-down hemoglobin combines with hydrogen sulfide to form iron sulfide, creating a permanent dark stain deep within the tooth structure.
Dental Caries and Progressive Decay
The most significant cause of black spots on teeth is dental caries, the scientific term for tooth decay. This process begins when acid produced by oral bacteria erodes the mineral structure of the enamel and underlying dentin. The dark coloration is not the decay itself but the result of staining and chemical changes within the damaged tooth structure.
As the decay progresses into the softer dentin, the dentinal tubules become exposed and stained by food pigments and metallic ions. The combination of bacterial debris, broken-down dentin, and staining products leads to the characteristic black or dark brown appearance. Active, rapidly progressing decay, however, may sometimes appear softer and lighter in color, often yellow or light brown, as it has not had time to absorb staining agents.
In contrast, a lesion that appears black and feels hard when probed is often arrested decay. This means the decay process has stopped, often due to improved oral hygiene or increased fluoride exposure, leaving a stable, dark, remineralized scar. While active decay requires intervention with a filling, arrested decay is often monitored and may not require surgical treatment. The presence of visible black holes or pits indicates that the decay has breached the enamel surface, signaling an advanced stage of bacterial destruction that threatens the tooth’s vitality.
Diagnosis and Treatment Options
A dentist’s diagnosis of the black discoloration begins with a visual examination and tactile probing to assess the texture of the affected area. This is followed by dental X-rays, which determine if the discoloration is caused by decay reaching internal structures or if it relates to a failing restoration. The treatment plan is strictly determined by the identified cause of the discoloration.
For extrinsic black staining caused by bacteria or diet, the solution is a professional dental cleaning involving scaling and polishing. If the discoloration is due to active dental caries, the decayed material must be removed and the tooth restored with a filling or a dental crown. Intrinsic discoloration from pulp necrosis requires root canal treatment to remove the dead tissue, followed by bleaching or a crown. Cosmetic options like veneers can cover permanent intrinsic stains, such as those caused by old amalgam fillings or trauma, that cannot be lightened otherwise.