Dental fillings do not lighten along with natural teeth during a whitening procedure. Tooth-colored restorations, such as composite fillings, porcelain veneers, or crowns, are made of synthetic materials that do not respond to the chemical agents used in whitening treatments. This resistance means that if you whiten your smile, your natural tooth structure will lighten, but any visible fillings will remain their original shade. The resulting color mismatch is a primary cosmetic concern for anyone considering teeth whitening with existing dental work.
The Composition of Dental Fillings
The lack of color change in fillings is due to the fundamental difference in material structure between natural teeth and the restorative compounds. The most common tooth-colored filling material is composite resin, which is a blend of a plastic resin matrix and finely powdered filler particles. The resin matrix is typically an acrylic plastic compound, while the filler is often a silicon-based material like glass or quartz.
These components are chemically inert and non-porous once hardened, meaning they do not possess the same organic matrix as a natural tooth. The shade of a composite filling is set at the time of placement and is designed to resist staining and chemical alteration. Older materials, such as amalgam fillings (metal alloys composed mainly of mercury, silver, and tin), are also unaffected by whitening chemicals.
Since composite resin and glass particles are not porous tissues, whitening agents cannot penetrate their structure to initiate a chemical change. The color stability of these restorations is an advantage for durability but becomes a disadvantage when a patient seeks to lighten their smile. Even porcelain restorations, which closely mimic natural tooth color, are highly resistant to the oxidative process of whitening.
How Teeth Change Color During Whitening
Natural teeth respond to whitening treatments because their structure is porous and contains organic molecules that can be altered. The primary agents used are hydrogen peroxide or carbamide peroxide. Carbamide peroxide breaks down into hydrogen peroxide, which then breaks down into reactive oxygen molecules.
These small oxygen molecules diffuse through the microscopic pores in the enamel layer and reach the underlying dentin. Dentin largely determines the tooth’s color and contains long-chain, pigmented molecules called chromogens. The reactive oxygen molecules chemically react with these chromogens through oxidation.
The oxidation reaction breaks the double-bonded carbon chains of the stain molecules into smaller, less pigmented, or colorless molecules. This chemical change causes the dentin to reflect light differently, making the tooth appear lighter. This mechanism relies on the peroxide diffusing into the organic tissue, a property synthetic filling materials lack entirely.
Addressing Color Mismatches After Whitening
Since fillings will not lighten, a color mismatch is almost certain if visible restorations are present when natural teeth are whitened. The practical solution for achieving a uniform smile color is to replace the existing restorations. The new filling material, whether composite or porcelain, is then shade-matched to the patient’s new, lighter tooth color.
Timing the replacement is crucial to ensure the new restoration perfectly blends with the final tooth shade. After whitening, the color of the natural teeth is not immediately stable. Dentists typically advise waiting 10 to 14 days following the last whitening session before any shade-matching dental work is performed.
This waiting period is necessary for color stabilization and rehydration. The tooth color initially appears brighter due to temporary dehydration from the whitening gel, and the shade needs time to stabilize to its final color. Waiting also allows residual oxygen from the peroxide to dissipate, which is important because oxygen can interfere with the bonding strength of the new filling.