A dental crown is a cap placed over a damaged or weakened tooth to restore its function, shape, and appearance. These restorations are crafted from durable materials like porcelain, ceramic, or composite resin, which are designed to mimic the look of a natural tooth. However, a fundamental truth about these caps is that standard chemical whitening procedures, often called bleaching, will not work on them. This inability to change color means that any attempt to brighten a smile that includes crowns must account for the fixed shade of the restoration.
Why Standard Whitening Methods Will Not Work
Whitening agents fail to lighten crowns due to the fundamental difference between the crown material and natural tooth structure. Natural teeth have porous enamel and dentin layers containing organic material. Whitening gels, typically containing hydrogen peroxide or carbamide peroxide, penetrate these pores to break down internal stains through oxidation.
Crowns are made from highly dense, non-porous materials like porcelain or zirconia. These materials are chemically stable and lack the organic components that react with peroxide bleaching agents. The color of a ceramic crown is fixed during manufacturing, essentially being “baked in” to the final product. Using a bleaching agent on a crown will only lighten the surrounding natural teeth, resulting in a noticeable color mismatch where the crown appears darker than before.
What Causes Crowns to Look Darker or Stained
When a crown appears darker or discolored, it is not due to a chemical change in the restoration itself but rather a few distinct issues. One common cause is extrinsic staining, which involves the accumulation of colored substances on the crown’s surface. Just like natural teeth, the crown’s surface can attract pigments from coffee, red wine, tea, or tobacco products, especially if its protective glaze has worn down.
Another source of discoloration is an intrinsic mismatch, where the crown’s fixed shade no longer aligns with the surrounding teeth. This often occurs when a patient whitens their natural teeth after the crown was placed, making the crown look relatively darker. A darker appearance can also be caused by underlying issues, such as the exposure of a dark metal margin near the gum line in older porcelain-fused-to-metal crowns, or the darkening of the natural tooth structure beneath the crown due to decay or a non-vital nerve.
Options for Achieving a Uniformly Whiter Smile
Since the crown’s color cannot be chemically altered, achieving a whiter, uniform smile focuses on two main approaches: cleaning the surface or changing the restoration. The first step is a professional cleaning and polishing performed by a dental hygienist to remove extrinsic surface stains. This process helps restore the crown to its original shade by removing accumulated plaque and surface discoloration.
For patients seeking a significantly brighter smile, the most reliable path involves whitening the natural teeth first. The patient should undergo professional teeth whitening to achieve their desired shade across all natural teeth. Once the natural tooth color has stabilized, which typically takes about two weeks, the existing crown can then be replaced with a new one that is custom-matched to the lighter shade.
Crown replacement is the only way to intrinsically change the restoration’s color and is necessary if the underlying issue is an unresolvable shade mismatch or a structural problem like exposed metal. This procedure allows the dentist to select a modern, all-ceramic material, such as porcelain or zirconia, that provides superior aesthetics and perfectly blends with the newly brightened smile. Coordinating the whitening of the natural teeth with the fabrication of a new crown ensures a completely uniform and brighter appearance.