A dark spot on a tooth often prompts concern about a cavity. While tooth decay is a serious possibility, less concerning factors can also cause discoloration. Understanding the potential origins, which range from simple surface stains to structural changes, can guide your next steps. Since the spot’s appearance alone does not determine its cause or severity, professional evaluation is the most prudent course of action.
Tooth Decay and Cavity Formation
Dental decay begins with demineralization. Plaque bacteria consume dietary sugars and produce acids, which leach minerals from the enamel. This initial damage often appears as a white spot, indicating a loss of density.
If acid production continues, the decay penetrates the enamel and reaches the underlying dentin, which is softer and more porous. The resulting dark color is often a combination of stained dentin and the shadow cast by the breakdown of the tooth structure. Active cavities are progressing lesions that require intervention.
A dark spot may also represent an arrested lesion, meaning the decay process has stopped. This occurs when the balance shifts toward remineralization, often due to improved oral hygiene or fluoride exposure. Arrested decay is typically dark brown or black and feels hard and smooth, unlike active decay, which is softer and may appear a lighter brown or yellow.
Surface Stains from Diet and Lifestyle
Not all dark spots indicate structural damage; many are extrinsic stains adhering to the outer enamel surface. These stains result from chromogens, or color-producing compounds, present in various foods and beverages. Common culprits include deeply pigmented liquids like coffee, tea, red wine, cola, and certain dark berries.
Tobacco use introduces tar and nicotine compounds that easily adhere to the tooth surface, leading to stubborn discoloration. Another cause is chromogenic bacteria, which produce dark pigments when reacting with iron in saliva. These bacteria often form a distinct black line along the gumline, particularly in children.
These external stains are cosmetic and do not compromise the tooth structure. They are often resistant to regular brushing because they become embedded in the plaque layer. Professional dental cleaning and polishing are effective at removing these discolorations.
Spots Caused by Internal Factors
Some dark spots originate from within the tooth structure, independent of external factors or surface decay. Old dental restorations, specifically silver amalgam fillings, are a common cause of internal discoloration. Metallic components in the amalgam can slowly leach into the surrounding dentin over time.
This process causes the entire tooth to take on a blue-gray or dark tint, known as amalgam staining. Since enamel is translucent, the dark color of the underlying metal or stained dentin shows through. This discoloration does not necessarily mean the filling is failing or that new decay is present.
Another intrinsic factor is dental trauma, which can cause the internal nerve and blood vessels to die, a condition called pulp necrosis. When blood breaks down inside the tooth, the resulting byproducts stain the dentin from the inside out, causing the tooth to gradually turn gray or black. This discoloration often appears long after the initial injury.
When to See a Dentist
Given the wide range of potential causes, self-diagnosis of a dark spot is unreliable. A dental professional is equipped to accurately determine the origin and severity of the discoloration. The diagnostic process involves a thorough visual examination and tactile probing to check the spot’s texture, noting whether it is hard or soft.
X-rays are an important diagnostic tool, as they can reveal decay that has progressed beneath the enamel or under an existing filling. Treatment depends entirely on the diagnosis; a spot identified as arrested decay may only require monitoring and fluoride application. Active decay, however, requires restorative treatment, such as a filling or a crown, to prevent the infection from spreading into the tooth’s pulp.