Dental restorations, commonly called fillings, repair teeth damaged by decay. Many people notice a color change over time, leading to concern that the restoration has failed. Fillings can turn dark or black due to causes ranging from a benign chemical reaction in the material to a serious structural issue like new decay. Understanding the source of the discoloration is necessary to determine if the filling requires replacement.
How Filling Materials Naturally Darken
Amalgam, the most common metallic dental material, is a mix of metals including silver, tin, copper, and mercury. This composition leads to surface darkening known as tarnish in the chemically reactive oral environment. Tarnish occurs when the silver in the amalgam reacts with sulfur compounds found in saliva. This chemical reaction forms silver sulfide, a black compound that coats the exterior of the restoration.
This surface discoloration is generally considered an aesthetic issue and does not indicate structural failure. A more severe chemical reaction is corrosion, a deeper deterioration caused by electrochemical forces in the acidic oral environment. Corrosion can lead to a bluish-black area around the margins of the filling. For amalgam, a dark, aged appearance is a normal consequence of its metallic nature and prolonged exposure.
When Darkening Signifies a Structural Issue
When blackening appears, the serious concern is that it indicates structural failure, such as recurrent decay or marginal leakage. Marginal leakage occurs when a gap forms between the edge of the filling and the surrounding tooth structure. This microscopic space allows oral fluids, bacteria, and staining agents to penetrate beneath the restoration.
This infiltration can lead to recurrent decay, a new cavity forming under the existing filling, appearing as a dark line or shadow. If a dark spot is visible specifically around the edge of the filling, it often signals that the protective seal has been compromised. Bacteria accumulating in the gap can continue to erode the tooth undetected.
Tooth-colored restorations, known as composite resins, are susceptible to staining from highly pigmented foods and beverages due to their slight porosity. However, a significant dark shadow on a composite filling is rarely benign. The material is subject to polymerization shrinkage upon placement, which can create micro-gaps that facilitate marginal leakage. Therefore, distinct blackening or dark staining around a composite filling frequently suggests a breach in the seal and potential structural failure.
Options for Addressing Discoloration
If a filling is dark, the first step involves a professional examination, including X-rays, to distinguish between simple surface tarnish and underlying structural failure. If the discoloration is purely cosmetic, such as surface tarnish on an amalgam filling without signs of decay, the dentist may recommend simple monitoring. In some cases, finishing and polishing can remove surface tarnish and revitalize the appearance of an otherwise sound restoration.
If the examination confirms marginal leakage or recurrent decay is the cause of the blackening, replacement is necessary to protect the tooth’s long-term health. The failing restoration is removed, the decay is cleaned out, and a new filling is placed.
Patients seeking aesthetic improvement often choose to replace old metallic fillings with tooth-colored alternatives, such as composite resin or porcelain inlays or onlays. Maintaining excellent oral hygiene, especially around the edges of any restoration, helps prevent the buildup of plaque and subsequent staining or marginal decay that causes darkening.