A dental filling is a restorative material used to repair a tooth damaged by decay or trauma. It seals the compromised area, preventing further bacterial invasion and restoring the tooth’s structure. Noticing a dark or black spot on a filling often causes concern, leading people to wonder if the discoloration signals a new cavity or a failing restoration. This darkening is a frequent occurrence that can be attributed to several factors, ranging from the material’s inherent properties to a potential new issue.
Material Changes in Dental Fillings
The most common reason for a filling to turn black is the nature of the material itself, particularly dental amalgam. Amalgam fillings, often called silver fillings, are an alloy primarily composed of silver, tin, and copper, mixed with liquid mercury. As a metallic restoration, amalgam reacts continuously with the moist, sulfur-containing environment of the mouth.
This reaction leads to tarnish, where a thin film of metallic sulfide forms on the surface of the filling. Tarnish appears as a black or dark gray discoloration, which is largely superficial and does not indicate a structural failure. Over time, a process called corrosion can occur, causing the metallic components to deteriorate by reacting with moisture and oxygen. This corrosion also contributes to the dark appearance, representing a deeper chemical change than simple surface tarnish.
In contrast, composite resin fillings are tooth-colored and do not tarnish like metals. However, composite materials are porous and susceptible to absorbing pigments from external sources. If a composite filling appears dark, the cause is generally related to external staining rather than an internal chemical change in the material.
Identifying External Staining Versus Internal Decay
Distinguishing between a harmless stain and a serious problem requires understanding the location and cause of the discoloration. External staining occurs when dark pigments from food, drinks, or tobacco deposit onto the filling’s surface or within the pores of a composite material. Common culprits include coffee, tea, red wine, dark sodas, and tobacco use. This type of discoloration is usually cosmetic and can often be removed with a professional dental cleaning and polishing.
A more serious cause for a black filling is secondary or recurrent decay, which is a new cavity forming around the existing restoration. This decay manifests as a dark shadow or line, often visible at the margins where the filling meets the natural tooth structure. If a small gap or microleakage develops at this margin, bacteria and food debris can seep underneath the filling, leading to new decay.
The visual darkening at the margin is either the decay itself or a shadow cast by the decay underneath the filling. Signs that a dark spot may be decay include a rough or chipped edge on the filling, or new sensitivity to hot, cold, or sweet foods. Decay requires attention because it indicates the restoration is failing to protect the tooth.
Professional Assessment and Treatment Pathways
Noticing a dark spot on a filling should prompt a visit to a dental professional, as self-diagnosis is unreliable for determining the cause and severity. A dentist will perform a visual examination and use specialized instruments, like a dental explorer, to check the texture and integrity of the filling and its margins. A smooth surface is more likely to be tarnish or staining, while a rough or sticky spot may indicate decay.
To confirm the presence and extent of decay, the dentist will take digital X-rays. X-rays are essential because they can reveal decay hidden underneath the filling or located between the teeth, which is not visible during a surface examination. The resulting diagnosis determines the appropriate course of action.
If the discoloration is confirmed to be simple tarnish on an amalgam or external staining on a composite, treatment may involve monitoring the area or polishing the filling. If the assessment identifies recurrent decay or a structural fracture, replacement is necessary. This procedure involves removing the old filling material, clearing all the decay, and placing a new restoration. Patients often opt to replace an old, dark amalgam with a tooth-colored composite for improved aesthetics during this process.