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Effects of Coffee Prepared with Different Milk Types on the Color Stability and Surface Roughness of Resin-Based Composites

This study demonstrates that while bovine milk mitigates coffee-induced discoloration in resin-based composites, oat milk exacerbates it—particularly in single-shade universal materials—though surface roughness remains clinically acceptable across all tested milk types.

Original authors: elif nihan küçükyıldız, Melek Güven BEKDAŞ

Published 2026-07-07

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: elif nihan küçükyıldız, Melek Güven BEKDAŞ

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your teeth are like a pristine white canvas, and the fillings dentists use (resin-based composites) are like high-tech paint. This study asked a simple question: What happens to this "paint" when you soak it in coffee, and does it matter if you add different kinds of milk to the cup?

The researchers wanted to see if the "paint" would get stained (lose its color) or get rough (like sandpaper) after being soaked in coffee for a long time. They tested two types of modern dental fillings and five different "coffee baths": plain water, black coffee, coffee with cow's milk, coffee with oat milk, and coffee with almond milk.

Here is the breakdown of their findings using some everyday analogies:

1. The Two Types of "Paint"

The study compared two specific dental materials:

G-ænial A'CHORD: Think of this as a traditional, multi-colored paint mixed with tiny glass beads.
Omnichroma: This is a newer, "smart" paint that uses a special trick to match your natural tooth color without needing different shades. It's like a chameleon that blends in perfectly.

The Result: The "smart" paint (Omnichroma) was much more sensitive to staining than the traditional one. When soaked in coffee, the Omnichroma paint changed color much more dramatically, especially if the coffee was black or mixed with oat milk. The traditional paint (G-ænial) held its color better, though it still got a little dirty.

2. The Coffee Baths: Who Stained the Most?

The researchers soaked the samples for 12 days (which they say is like drinking coffee for a whole year).

Black Coffee (The Heavy Stainer): This was the worst offender. It acted like a strong dye, turning the samples a darker color. The "smart" paint (Omnichroma) turned the darkest here.
Oat Milk Coffee (The Surprising Stainer): You might think milk protects against stains, but oat milk didn't help much. In fact, the oat milk coffee caused almost as much staining as the black coffee. The researchers suggest this is because oat milk is thick and sticky (like syrup), which might have helped the coffee's dark pigments stick to the surface longer.
Almond Milk Coffee: This was in the middle. It stained the samples, but not quite as badly as the oat milk or black coffee.
Cow's Milk Coffee (The Protector): This was the winner. Adding cow's milk to the coffee acted like a shield. It significantly reduced the staining compared to black coffee. The researchers believe the proteins in cow's milk (specifically casein) act like little magnets that grab the coffee's dark particles before they can stick to the dental "paint."

3. The "Sandpaper" Test (Surface Roughness)

Besides color, the researchers checked if the coffee made the surface rough. Imagine running your tongue over a smooth tile versus a piece of sandpaper. Rough surfaces trap dirt and bacteria.

The Good News: In almost every single group, the surface stayed smooth enough to be considered safe and healthy (below the "roughness limit" of 0.2 micrometers).
The One Exception: The only time the surface got noticeably rougher was when the "smart" paint (Omnichroma) was soaked in black coffee. It became slightly more like sandpaper, but still within safe limits.
The Milk Effect: Interestingly, adding milk (whether cow, oat, or almond) seemed to keep the surfaces smoother than black coffee alone. It's as if the milk components buffered the harshness of the coffee.

4. The Big Takeaway

The study concluded that not all milks are created equal when it comes to protecting your dental work from coffee stains.

Cow's milk is the best friend for your fillings, acting like a protective barrier that stops coffee from staining them.
Oat milk, despite being popular, didn't offer that same protection and might even make the staining worse for certain types of dental materials.
Black coffee is the enemy of color stability, especially for the newer "smart" fillings.

Important Note: The researchers found that getting stained (color change) and getting rough (surface texture) didn't necessarily happen together. A filling could get very dark without getting rough, or vice versa.

In short, if you love coffee and have dental fillings, the type of milk you choose might actually change how quickly your smile loses its sparkle. Cow's milk seems to be the best guard against the coffee stain, while oat milk might let the coffee do its dirty work.

Technical Summary: Effects of Coffee Prepared with Different Milk Types on the Color Stability and Surface Roughness of Resin-Based Composites

Problem Statement
Resin-based composites are widely utilized in restorative dentistry due to their aesthetic and mechanical properties; however, their long-term clinical success is compromised by extrinsic factors, particularly chromogenic beverages like coffee. Coffee causes significant discoloration through the penetration of low-polarity coloring agents into the resin matrix. While the staining potential of black coffee is well-documented, there is limited data regarding how coffee prepared with different milk types—specifically bovine milk versus plant-based alternatives (oat and almond milk)—affects the color stability and surface roughness ( $R_a$ ) of modern composite materials. This study addresses the gap in understanding how these dietary variations influence the aesthetic longevity of restorations.

Methodology
The study employed an in vitro experimental design using 80 disc-shaped specimens (8 mm diameter, 2 mm thickness) fabricated from two distinct resin-based composites:

G-ænial A'CHORD: A nanohybrid composite.
Omnichroma: A single-shade universal composite utilizing structural coloration.

Specimens were divided into five immersion groups (12 days, 37°C, daily solution replacement):

Distilled water (control)
Black coffee
Coffee + Bovine milk (5% v/v)
Coffee + Oat milk (5% v/v)
Coffee + Almond milk (5% v/v)

Measurements:

Color Stability: Measured using a digital spectrophotometer (VITA Easyshade V) before ( $T_0$ ) and after ( $T_1$ ) immersion. Color change was calculated as $\Delta E_{00}$ using the CIEDE2000 system, with a clinically acceptable threshold set at 1.8.
Surface Roughness ( $R_a$ ): Evaluated using a contact profilometer (Taylor Hobson Surtronic S-128) at baseline and post-immersion. The clinically acceptable threshold for $R_a$ was set at 0.2 µm.

Statistical Analysis:
Data were analyzed using Two-Way ANOVA, Welch ANOVA, Kruskal–Wallis H tests, and appropriate post-hoc tests (Tamhane's T2, Dunn–Bonferroni) with a significance level of $p < 0.05$ .

Key Results

Color Change ( $\Delta E_{00}$ ): Beverage type significantly affected color change in both materials ( $p < 0.001$ $p < 0.001$ ).
- Material Comparison: Omnichroma exhibited significantly higher $\Delta E_{00}$ values than G-ænial A'CHORD, particularly in black coffee and oat milk coffee groups. In the distilled water control, G-ænial A'CHORD showed higher discoloration than Omnichroma.
- Milk Effects: Among coffee-containing groups, the bovine milk coffee group demonstrated the lowest color change for both materials. Conversely, oat milk coffee was associated with the highest color change, particularly in Omnichroma.
- Thresholds: All groups exceeded the visual perception threshold (0.8), and most coffee groups exceeded the clinically acceptable limit (1.8), except for the bovine milk coffee group in G-ænial A'CHORD which remained close to or below the limit depending on the specific comparison.
Surface Roughness ( $R_a$ ):
- All final $R_a$ values remained below the clinically acceptable threshold of 0.2 µm.
- A statistically significant increase in $R_a$ was observed only in the Omnichroma black coffee group ( $p = 0.024$ ). No significant changes were found in other groups or in the G-ænial A'CHORD material.
- The change in roughness ( $\Delta R_a$ ) was significantly lower in almond and oat milk groups compared to distilled water and black coffee groups.
Correlation: No statistically significant correlation was found between color change ( $\Delta E_{00}$ ) and surface roughness change ( $\Delta R_a$ ) ( $p > 0.05$ ).

Significance and Claims
The study concludes that the type of milk added to coffee significantly influences the staining behavior of resin-based composites.

Protective Effect of Bovine Milk: The addition of bovine milk reduced coffee-induced discoloration, likely due to casein proteins interacting with chromogenic pigments and reducing their adhesion to the composite surface.
Risk of Plant-Based Alternatives: Oat milk was associated with greater color change compared to bovine milk, potentially due to its high viscosity (from $\beta$ -glucan) retaining pigments longer on the surface and the absence of casein-like binding proteins.
Material Sensitivity: The single-shade universal composite (Omnichroma) demonstrated higher sensitivity to chromogenic solutions, particularly black and oat milk coffee, compared to the nanohybrid composite (G-ænial A'CHORD).

The authors assert that these findings are important for predicting the long-term clinical performance of aesthetic restorations, suggesting that dietary habits involving plant-based milk alternatives may impact the aesthetic stability of composites differently than traditional bovine milk. The study acknowledges limitations regarding its in vitro nature and the inability to fully simulate the complex oral environment (saliva, mechanical abrasion, thermal changes), noting that further clinical studies are required.

1. The Two Types of "Paint"

2. The Coffee Baths: Who Stained the Most?

3. The "Sandpaper" Test (Surface Roughness)

4. The Big Takeaway

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