The photoinduced polymerization of monomers is currently an essential tool in various industries. The photopolymerization process plays an increasingly important role in biomedical applications. It is especially used in the production of dental composites. It also exhibits unique properties, such as a short time of polymerization of composites (up to a few seconds), low energy consumption, and spatial resolution (polymerization only in irradiated areas). This paper describes a short overview of the history and classification of different typical monomers and photoinitiating systems such as bimolecular photoinitiator system containing camphorquinone and aromatic amine, 1-phenyl-1,2-propanedione, phosphine derivatives, germanium derivatives, hexaarylbiimidazole derivatives, silane-based derivatives and thioxanthone derivatives used in the production of dental composites with their limitations and disadvantages. Moreover, this article represents the challenges faced when using the latest inventions in the field of dental materials, with a particular focus on photoinitiating systems based on iodonium salts. The beneficial properties of dental composites cured using initiation systems based on iodonium salts have been demonstrated.

Herein, a review of the literature on polymerization shrinkage occurring in dental composites was presented.

Herein, new iodonium salts based on a 4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indecene (B-1) chromophore have been introduced to 3D printing applications. Iodonium salts with different anions such as tosylate, hexafluorophosphate, hexafluoroantimonate, and triflate absorbing in the range up to 600 nm are reported. The usefulness of the new BODIPY derivatives in initiating cationic photopolymerization processes such as epoxide, vinyl ether, oxetane, and glycidyl monomers in the wavelength range from 365 to 520 nm was confirmed using real-time FT-IR and photo-DSC methods. The initiation efficiency of a one-component system was also compared with that of a two-component system consisting of the chromophore (the same as that used for conducting iodonium salts) and iodonium salt – bis-(4-t-butylphenyl)-iodonium hexafluorophosphate. Moreover, the photochemical mechanisms were investigated by steady-state photolysis, ESR fluorescence experiments, theoretical calculations of molecular orbitals, and electrochemical analysis. These studies allowed us to determine the effect of the anion type in iodonium salts on the rate of proton acid generation. The BODIPY derivatives are also efficient for the initiation of cationic and free-radical polymerization. Optical microscopy experiments demonstrated that different patterns can be obtained by experiments with resolution test targets and 3d-printing. Moreover, photoinitiators based on the B-1 chromophore can be used not only for initiating the photopolymerization processes but also as colorimetric sensors for measurements of the degree of photopolymerization.