Effects of Resin Coatings and Thermocycling on the Surface and Mechanical Properties of a High-Viscosity Glass Ionomer Cement: An In Vitro Study
This in vitro study demonstrates that while resin coatings (EQUIA Forte Coat and G-COAT PLUS) significantly mitigate surface deterioration and enhance the flexural strength of high-viscosity glass ionomer cement compared to uncoated specimens under thermocycling, they do not completely prevent property changes or color shifts after prolonged thermal ageing.
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
In the world of dental restoration, some materials are designed to mimic the natural tooth so closely that they become part of the living structure. Glass ionomer cements are among these materials. They are made from a mixture of glass particles and acid, which react to form a solid that bonds chemically to the tooth and releases fluoride to help prevent decay. However, these materials have a vulnerable period right after they are placed. While they are hardening, or maturing, they are sensitive to their environment. If they dry out too quickly or absorb too much water before they are fully set, their strength and durability can be compromised. To protect them, dentists often apply a thin, liquid coating that hardens under a special light, creating a shield while the material settles. But a question remains: does this shield hold up over time when the material is subjected to the constant hot and cold shocks of eating and drinking?
Researchers at the University of Malaya set out to answer this by testing a specific, modern type of glass ionomer cement known as EQUIA Forte HT. They wanted to see how two different protective coatings performed when the material was subjected to extreme temperature changes, simulating years of use in the mouth. To do this, they created hundreds of small, uniform samples of the cement. They divided these samples into groups: some were left bare, while others were coated with one of two commercially available resin sealers. Then, they subjected these samples to a rigorous test involving thousands of cycles of dipping them into hot water at 55 degrees Celsius and cold water at 5 degrees Celsius. This process, known as thermocycling, mimics the stress of drinking hot coffee followed by a cold drink, a routine that can cause materials to expand and contract repeatedly.
The study revealed that the protective coatings made a significant difference, but not in every way the researchers might have hoped. When the samples were left uncoated, the repeated temperature changes took a visible toll. Their surfaces became rougher and more pitted, and they changed color more noticeably than the coated samples. The uncoated material also became weaker, losing a substantial amount of its ability to resist bending forces after just a few thousand cycles. In contrast, the samples covered with resin coatings maintained much smoother surfaces and retained more of their original color. The coatings acted as a barrier, preventing the surface from degrading as quickly as the bare cement did. Furthermore, the coated samples were generally stronger than the uncoated ones, suggesting that the seal helped preserve the material's structural integrity.
However, the protection was not absolute. Even with the coatings, the materials still changed over time. The color of all the samples, including the coated ones, shifted enough to be noticeable to the human eye after the full 10,000 cycles of testing. While the coated samples changed less than the bare ones, the difference in color eventually crossed the threshold of what is considered acceptable for a natural-looking restoration. Additionally, the researchers found that the two different coatings did not perform exactly the same. One of the coatings, G-COAT PLUS, kept the color change within acceptable limits for a longer period during the later stages of the test compared to the other coating, but neither could stop the changes entirely. The study also noted that the hardness measurements for the coated samples were actually measuring the hardness of the resin shield itself rather than the cement underneath, meaning the coating was thick enough to protect the surface but also dominated the test results for that specific property.
Ultimately, the research suggests that while resin coatings are effective tools for protecting glass ionomer cements from the immediate damage of temperature swings, they are not a permanent solution against the slow, cumulative effects of aging. The coatings successfully reduced surface roughness and kept the material stronger for longer, but they could not completely prevent the material from changing color or deteriorating under prolonged stress. The findings confirm that these protective layers are valuable for maintaining the quality of a restoration during its early life, but they do not make the material immune to the long-term wear and tear of the oral environment. For patients and dentists, this means that while applying a coating is a wise step to ensure a restoration lasts, the material will still undergo changes over time that may eventually require attention.
Drowning in papers in your field?
Get daily digests of the most novel papers matching your research keywords — with technical summaries, in your language.