12-10 pouring coffee

[Image above] Credit: Rawpixel

Before heading home to celebrate Thanksgiving last month, I realized I had a dentist appointment scheduled the same week. When I called to reschedule, however, the earliest appointment that would fit with my schedule was in May!

I am not alone in having difficulties scheduling a dental appointment. As people feel more comfortable returning to pre-pandemic routines, more people are making dental appointments at the same time that dental offices are facing staffing shortages, leading to sometimes long waits for appointments to become available.

While the situation is certainly frustrating, it is heartening to see the increased attention to oral health. While oral diseases are considered largely preventable through simple self-care intervention, their incidence remains stubbornly high—caries and periodontal disease are among the most prevalent noncommunicable diseases globally.

Fortunately, advances in dental materials and techniques during the last few decades have greatly reduced the chances of losing teeth when decay is detected. As outlined in the December 2020 Bulletin cover story on ceramic and glass biomaterials, there are multiple treatment options for dental caries depending on how far advanced they are, including restoration with a crown when a majority of the tooth is lost.

Today, all-ceramic crowns—such as alumina, lithium disilicate, and yttria-stabilized tetragonal zirconia—are the most common crown type because of their strength, ease of fabrication, and aesthetics. Some of these ceramic crowns are relatively new to the marketplace, however, and researchers are still learning what factors affect the performance of these crowns in the long term.

Lithium disilicate glass-ceramics are a newer crown material known for excellent color stability, surface gloss, luster, and favorable wear resistance. Studies exist on the acidic effect of coffee beverages or whitening on lithium disilicate glass-ceramics, but limited information is available on the combined effect of coffee and different whitening systems on the surface texture.

In a recent open-access study, researchers from several universities in Saudi Arabia investigated the effect of a coffee beverage and two whitening systems (dental bleaching gels and whitening toothpaste) on the surface roughness and gloss of glazed lithium disilicate glass-ceramics.

The researchers cut, sintered, glazed, and heat-treated 68 disks of lithium disilicate for the experiment. All disks were immersed in a coffee solution (Dunkin’ Donuts Original Blend Ground Coffee, Medium Roast) for 12 consecutive days to simulate one year of drinking coffee. Following this step, the disks underwent one of four whitening treatments:

  1. No treatment (control group); kept moist in a saline solution that was changed daily.
  2. Brushed with distilled water only.
  3. Brushed with a suspension of whitening toothpaste and distilled water.
  4. Bleached using a simulated at-home bleaching protocol (15% carbamide peroxide).

The samples in groups 2 and 3 were brushed twice daily, corresponding to the brushing protocol recommended by the American Dental Association.

The researchers explain that they designed this setup to represent a clinical situation of patients drinking coffee and seeking whitening treatment to improve the aesthetics of their stained natural teeth along with their ceramic prosthesis. However, they note that the study does not reflect the exact physiological environment inside a human mouth, as there is no standardized protocol to mimic this environment.

Within this limitation, they determined that all glazed lithium disilicate disks experienced a significant increase in surface roughness after being subjected to coffee immersion and whitening systems, with brushed samples demonstrating the greatest change.

“Some studies showed no significant changes in Ra [surface roughness] after brushing alone or with whitening toothpaste,” the researchers write. “This inconsistency and differences in these results are due to the various testing protocols and the materials used, such as toothbrush bristle type, brushing time, force, and dentifrice abrasivity.”

On the other hand, coffee beverages and whitening systems did not appear to significantly affect surface gloss—which was a bit surprising. “In most dental materials, the Ra and gloss are usually, but not always, interrelated; our study showed that the Ra and surface gloss was not correlated for [lithium disilicate glass-ceramics],” the researchers write.

The open-access paper, published in Journal of Applied Biomaterials & Functional Materials, is “The effect of coffee and whitening systems on surface roughness and gloss of CAD/CAM lithium disilicate glass ceramics” (DOI: 10.1177/22808000211058866).