Why Are My Zirconia Crowns Turning Yellow?

Zirconia crowns are widely loved for their strength, durability, and natural tooth-like appearance. However, you might have noticed a frustrating issue: your beautiful zirconia crown is turning yellow. If you’ve been wondering why this is happening and what you can do about it, you’re in the right place. In this post, we will explain the possible causes of yellowing zirconia crowns, break down the science behind the discoloration, and offer practical solutions to maintain their aesthetic appeal.

What Makes Zirconia Crowns Popular? Why Are They Better Than Other Crowns?

Zirconia crowns are a top choice for dental restorations because of their many benefits. They’re strong, durable, and blend well with natural teeth. The most significant advantage, however, is their stain resistance. Unlike materials like porcelain-fused-to-metal (PFM) crowns or full porcelain crowns, zirconia crowns are significantly less prone to staining.

Zirconia vs. PFM: While both materials are durable, zirconia is less porous, meaning it doesn’t absorb stains from food or beverages as easily as PFM or full porcelain. PFM crowns, for example, can absorb discoloration more readily, especially at the metal margin.
Zirconia vs. Porcelain: Full porcelain crowns, although aesthetic, are more susceptible to staining, especially if the crown is not properly polished during manufacturing.

However, while zirconia is highly resistant to stains, it’s not entirely immune to them. So, let’s dive into the reasons why your zirconia crown might be turning yellow.

External Stains: The Usual Culprits

Even though zirconia crowns are less porous than other materials, they can still absorb external stains, especially if their surface is roughened. Let’s look at the types of external stains:

Organic Stains: Foods like tea, coffee, berries, and pomegranates are notorious for leaving stains on dental work. These foods contain chromogens and tannins—pigments and compounds that easily stick to the surface of zirconia. Even if zirconia isn’t as porous, these pigments can latch onto microscopic surface grooves, leading to discoloration.
Inorganic Stains: Drinks like soda or vinegar can etch the surface of zirconia, allowing more pigments to settle into the material. While these types of stains are less common, they can still cause the crown to appear yellowish over time.

The Polishing Process and Surface Texture: Why Smoothness Matters

The way your zirconia crown is polished during manufacturing can greatly impact how easily it stains. A less smooth surface may be created if the polishing process isn’t thorough or if the material is too rough during manufacturing. Here’s why it matters:

Polishing Process: Zirconia crowns are polished to give them a smooth, shiny finish. However, if the polishing process is not done to perfection, tiny surface irregularities can remain. These irregularities create microscopic grooves that trap food particles and staining pigments.
Smooth Surface for Stain Resistance: When zirconia is polished correctly, its smooth surface makes it much harder for stains to adhere. Crowns with a glossy finish are more resistant to discoloration and easier to clean.

Internal Discoloration: What You Need to Know

While external stains are the most common cause of yellowing, internal discoloration is a less likely but possible issue. Bonding agents used to secure the crown or slight material degradation over time could result in yellowing.

Bonding Agent Degradation: Bonding materials can degrade or discolor over long periods, which may cause the crown to lose its original hue, though this is rare.
Material Degradation: Studies have shown that while zirconia is highly durable, over a long period, the material may slowly degrade. The color change, however, is minimal unless the crown has been poorly manufactured or has experienced some wear and tear.
Microfractures and Trapping Stains: Tiny cracks can form in the zirconia crown over time, especially if it’s subjected to heavy biting forces. These fractures may trap stains that are harder to remove.

Poor Oral Hygiene: How It Contributes to Yellowing

Your zirconia crown can also turn yellow if you don’t maintain proper oral hygiene. The biofilm that forms in your mouth contains bacteria that can contribute to stain adherence. This happens because:

Plaque Build-Up: Plaque and bacteria can stick to zirconia, even though it’s less porous than other materials. If not properly removed, the plaque can harden into tartar, which may contribute to a yellowish hue on the crown.
Specific Bacteria: Certain types of bacteria in the biofilm can cause color changes in dental restorations. These bacteria feed on food particles and can secrete pigments that stain the crown over time.

The Importance of Professional Dental Cleaning

While brushing and flossing at home is essential, professional cleaning is necessary to maintain the aesthetic of your zirconia crown. During a routine dental cleaning, your hygienist uses specialized tools and polishing agents specifically designed for zirconia crowns:

Polishing Pastes: Dental professionals often use non-abrasive pastes that gently remove surface stains without damaging the zirconia.
Ultrasonic Instruments: These instruments can effectively remove plaque and tartar from hard-to-reach areas around the crown, restoring its shine.

When to Consult Your Dentist: Look for These Visual Cues

If you notice any of the following, it might be time to visit your dentist:

Yellowing at the Gumline: A yellow line at the base of your crown could indicate discoloration caused by plaque build-up or marginal leakage.
Opaque Patches: If the yellowing appears in patches rather than being evenly distributed, it could be a sign of internal degradation or bonding agent failure.

Can You Whiten a Zirconia Crown?

Zirconia crowns are chemically inert, meaning they don’t react with traditional teeth whitening products. Teeth whitening works by chemically altering the color of the tooth enamel, but this doesn’t work on zirconia since it’s a non-reactive ceramic material.

Chemical Mechanism: Whitening products typically rely on hydrogen peroxide or carbamide peroxide to break down stain molecules in tooth enamel. Since zirconia does not have the same organic structure as natural teeth, these chemicals cannot alter its color.

Maintain Excellent Oral Hygiene: Keep Your Crown Clean

To prevent further yellowing, here are some effective tips for keeping your zirconia crown looking fresh:

Brushing Techniques: Use gentle circular motions when brushing around the crown to avoid scratching the surface. Always use a non-abrasive toothpaste designed for dental restorations.
Flossing: Use PTFE floss, which is smoother and less likely to cause damage to the crown or irritate the gumline.

Be Mindful of Your Diet: Timing Matters

Certain foods and drinks are more likely to stain your zirconia crown. Here’s how to minimize their effect:

Consume Staining Foods with Meals: If you consume staining foods like berries or coffee, try to have them during meals, which allows you to rinse your mouth immediately afterward. This minimizes the time the pigments stay in contact with your crown.

Regular Dental Checkups: Keep an Eye on Your Crown’s Health

Routine dental visits are crucial for monitoring the condition of your zirconia crown. Your dentist can:

Assess the Integrity: Check for any cracks, chips, or changes to the crown’s surface that could lead to discoloration.
Catch Staining Early: Detect early signs of staining or plaque buildup that you might not notice.

Myth vs. Fact: Debunking Common Misconceptions About Zirconia Crowns

Myth: Zirconia crowns never stain.

Fact: While zirconia is highly resistant to staining, it can still discolor due to external stains, biofilm, or poor polishing.

Myth: Whitening products can restore the color of zirconia crowns.

Fact: Whitening products do not work on zirconia since it is chemically inert and cannot react with whitening agents.

Conclusion:

While zirconia crowns are durable and stain-resistant, they aren’t entirely immune to discoloration. Understanding the causes of yellowing and maintaining excellent oral hygiene will help you keep your crown looking beautiful for years. If you’re concerned about the yellowing or condition of your crown, don’t hesitate to consult your dentist. Regular dental checkups are essential for ensuring the long-term health and aesthetics of your zirconia crowns.

Take action today! Schedule your next dental checkup and keep your zirconia crown looking as good as new!