Grey stains on teeth are a distinct form of discoloration that often originates from within the tooth structure, known as intrinsic staining. Unlike the more common yellow or brown extrinsic stains that form on the tooth surface, grey discoloration is embedded deep within the dentin or results from internal damage. This internal location is why standard over-the-counter whitening methods often fail to resolve the issue, as the bleaching agents cannot penetrate deeply enough. Effectively treating grey stains requires specific professional interventions that address the underlying cause, whether it involves masking the color or bleaching the stain from the inside out.
Why Teeth Develop Grey Stains
Grey discoloration typically signals a fundamental change to the tooth’s core structure, stemming from three primary causes.
Tetracycline Staining
Tetracycline antibiotics are a frequent source, resulting from ingestion during the critical period of tooth formation, from the second trimester in utero up to about eight years of age in children. The drug binds chemically to calcium ions within the developing dentin and enamel, forming a permanent complex. Initially, this complex may appear fluorescent yellow, but upon exposure to light, it oxidizes, changing permanently to a non-fluorescent brown or blue-grey shade that is visible through the translucent enamel.
Trauma and Pulp Necrosis
Dental trauma can lead to the death of the tooth’s internal pulp tissue, a condition called pulp necrosis. A severe blow can sever the blood supply at the tooth’s root, causing internal bleeding within the pulp chamber. The subsequent breakdown of blood components, specifically the hemoglobin, releases iron sulfides and other dark-colored degradation products. These dark molecules then seep into the microscopic dentinal tubules, staining the tooth from the inside and causing it to appear dark grey or bluish-black.
Amalgam Fillings
Older silver amalgam fillings can also cause a blue-grey shadow, particularly in teeth with thin enamel. Over time, metallic ions, including silver and mercury from the filling material, can leach into the surrounding dentin, causing a permanent stain. Alternatively, the deep, dark color of a large amalgam filling can simply show through the natural, slightly translucent tooth structure, creating a dark, greyish appearance.
Professional Solutions for Grey Discoloration
Masking Severe Discoloration
For widespread and severe intrinsic discoloration, such as significant tetracycline staining, the most effective solution is often the application of dental veneers or crowns. Porcelain veneers are thin, custom-made shells bonded to the front surface of the tooth, acting as an opaque mask to completely hide the underlying grey color. Dental crowns, which cover the entire tooth, are typically reserved for cases where the discoloration is extremely dark or the tooth is already heavily restored or structurally compromised.
Internal Bleaching
For a single tooth that has turned grey following trauma and subsequent root canal treatment, a conservative procedure called internal bleaching is the treatment of choice. This method, sometimes called the “walking bleach” technique, involves placing a powerful bleaching agent, such as sodium perborate mixed with hydrogen peroxide, directly inside the emptied pulp chamber. The oxidizing agent works from the inside of the tooth to break down the dark pigment molecules that have stained the dentinal tubules. The agent is sealed in the tooth for several days and replaced until the desired shade is achieved, effectively lightening the tooth without external restoration.
Bonding and Microabrasion
Less extensive grey discoloration, such as localized spots or minor dark shadows, can often be addressed with dental bonding. This minimally invasive, single-visit procedure involves applying a tooth-colored composite resin directly to the tooth surface. The resin is expertly sculpted and polished to match the surrounding enamel, masking the grey area with a durable, tooth-colored material. For very superficial stains limited to the outermost layer of enamel, a technique called microabrasion can be used. This process uses a mild acid-abrasive slurry to mechanically remove a micro-thin layer of stained enamel, which is only effective if the discoloration is less than 0.2 millimeters deep.
Prevention and the Limits of Home Whitening
Limits of Home Whitening
The fundamental reason over-the-counter (OTC) or even professional external whitening treatments are ineffective against grey stains is the location of the discoloration. OTC products are designed to penetrate the outer enamel layer and break down stains on the surface (extrinsic stains). Grey stains, however, are deeply embedded within the dentin, below the enamel, making them unreachable by the topical bleaching gels used in home kits. The grey or blue-grey hue is a clear sign that the stain is intrinsic, meaning any attempt to lighten it from the outside will likely fail.
Preventing Tetracycline Staining
Preventing tetracycline staining involves strictly adhering to medical guidelines that advise against prescribing tetracycline antibiotics to pregnant women and children under the age of eight. During this developmental window, the antibiotic can chelate with calcium and become permanently incorporated into the forming tooth structure. Safer, alternative antibiotics should be used to prevent this permanent discoloration.
Preventing Trauma and Amalgam Stains
Preventing trauma-related grey teeth focuses on protecting the dental pulp from impact. Wearing a custom-fitted mouthguard is highly effective for individuals participating in contact sports or activities with a risk of facial injury. The mouthguard absorbs and disperses the force of a blow, which can prevent the internal hemorrhage and subsequent pulp death that leads to a grey tooth. The grey shadow caused by amalgam fillings can be prevented by opting for tooth-colored alternatives like composite resin, glass ionomer, or ceramic materials, which do not leach dark metallic ions into the tooth structure.