Behind the smooth shine of a dental filling or the strength of a composite material used in various industries lies a complex scientific process: ultraviolet (UV) light exposure. Most people may recognize UV light only as a cause of sunburn or a source of vitamin D. However, in materials science, UV light plays a vital role in transforming synthetic substances into strong and durable materials.

In-depth understanding of this comes from a study conducted by a group of Indonesian researchers, including Libianko Sianturi from the Graduate Program in Physics at Universitas Sumatera Utara and the Department of Electrical Engineering at Universitas HKBP Nommensen; Syahrul Humaidi, Timbangen Sembiring, and Erna Frida from the Graduate Program in Physics at Universitas Sumatera Utara; and Makmur Sirait from the Department of Physics at Universitas Negeri Medan. They systematically investigated how varying UV exposure durations affect the quality of UDMA/TEG-DMA composite resin, a material widely used in dentistry and manufacturing.

“Identifying the optimal exposure time is crucial for the resin to achieve its maximum strength and durability. If the exposure is too short, polymerization remains incomplete, weakening the material. On the other hand, prolonged exposure may generate excessive heat that degrades the polymer structure and reduces the resin’s performance,” said Syahrul Humaidi.

This composite resin is used for dental fillings, veneers, and even pressure-resistant components in industrial products. Essentially, the resin consists of small molecules that must form a dense, strong polymer network through UV-induced polymerization. The success of this process heavily depends on UV exposure time: too short, and the resin remains under-cured; too long, and it may overheat and deteriorate.

Polymerization begins when photoinitiators in the resin absorb UV energy, generating free radicals that trigger the chemical reaction binding monomers into polymers. In this study, a combination of two main photoinitiators was used: camphorquinone (CQ) and diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO). CQ is effective under visible light and facilitates good polymerization, while TPO absorbs UV light and accelerates curing. This blend allows faster and more efficient polymerization, enhancing the resin's strength and durability.

The study found that 90 minutes is the optimal UV exposure duration. At this point, the resin achieved the highest monomer-to-polymer conversion rate—77 percent—indicating that nearly all small molecules had transformed into a solid, stable polymer network. Humaidi explained that the resin’s surface at this duration was also the smoothest, improving adhesion and endurance, especially in dental applications.

Beyond maximum mechanical strength, the resin exposed for 90 minutes showed the lowest water absorption and minimal volume shrinkage. “These two factors are critical for the long-term resilience of the resin, preventing degradation and deformation that lead to early failure,” said Syahrul Humaidi.

The study also highlights the risks of improper curing durations. Resin cured for only 60 minutes did not reach complete polymerization, resulting in lower strength and hardness. Conversely, exposure longer than 120 minutes caused thermal degradation of the polymer network, reducing the material’s flexural strength and hardness due to overheating.

In dentistry, these findings are crucial. Dentists must ensure the proper curing time to create fillings or veneers that are not only strong and long-lasting but also comfortable for patients. Proper curing minimizes the risk of filling failure due to cracking or detachment, often caused by insufficient hardening. This contributes to better oral health outcomes and higher patient satisfaction.

In industry, composite resin is frequently used in components that must withstand pressure, impact, and harsh environments like temperature shifts, humidity, and chemical exposure. Resin cured for the optimal time exhibits superior mechanical and chemical resistance, making industrial products more reliable and long-lasting. This reduces maintenance and replacement costs while increasing production efficiency.

The research also opens pathways for developing more advanced resin curing technologies. By determining the ideal curing time and resulting resin properties, manufacturers can design more precise UV curing equipment, streamlining production without sacrificing quality. Furthermore, resin formulations can be optimized by adjusting photoinitiator types and concentrations to meet specific application needs.

Syahrul Humaidi noted, “We hope these findings can serve as a practical guide, both in dental clinics and industrial production lines, to significantly improve product quality and durability.” He also emphasized that this study is just a first step, with much more to explore, including long-term durability and the resin’s behavior in real-world environments.

In a world that increasingly demands high-performance materials and efficient production, research like this is vital. It shows how controlling a simple variable like UV exposure duration can significantly impact product quality. This underscores the important role of materials science and curing technology in driving innovation in healthcare and industry.

UV light—often overlooked—turns out to hold remarkable power in transforming basic materials into advanced substances that directly influence our health and quality of life. This research is a reminder that behind every technological advancement lies deep scientific inquiry and dedication worth appreciating.