The Latest Achievements in the Design of Permanent Fillings for Conservative Dentistry Based on Indenoquinoxaline Derivatives as Photoinitiators of Visible-Light Polymerization: Mass and Colour Stability.

The demand for polymer composite materials in the dental market is increasing every year. This rise is due to their excellent properties and ongoing technological advancements. The goal of this study was to develop new photoinitiators included in the liquid organic matrix, which is one of the main components of dental composites. Therefore, a series of compounds based on the indenoquinoxaline skeleton was synthesized, differing in the substituent. The spectroscopic properties of these compounds allowed their use as visible-light photoinitiators of radical polymerization in combination with (phenylthio)acetic acid. In addition to the polymerization kinetics, the lifetime and quantum yield of the triplet-state formation and the rate constants of its quenching by (phenylthio)acetic acid were determined. The durability of the designed composites was also assessed. Ageing tests included hydrothermal ageing, allowing for the determination of sorption, solubility, and mass change. Solutions imitating the oral cavity environment-distilled water, artificial saliva, n-heptane, and 3% acetic acid-as well as solutions containing pigments were used for these studies. Determination of the mass change and colour stability allowed for the assessment of how these materials react to long-term exposure in the oral environment. It was found that the solution simulating the natural oral environment has a significant impact on the hydrolytic stability and colour stability of the materials.