# Evaluation of the Impact of Various Functional Fillers on Key Properties of Dental Composites
## 1 Introduction  
Dental caries is classified as a bacterial disease affecting the hard tissues of the tooth. Its primary etiology lies in the presence of specific bacteria within the oral cavity. Among these, the most pronounced is anaerobic, Gram-positive _Streptococcus mutans_ (_S. mutans_) [1, 2, 3]. These microorganisms, present within dental plaque, metabolize dietary sugars, leading to the production of acids that demineralize and degrade tooth structures [1, 2, 3, 4, 5]. Modern dentistry provides various solutions for reconstructing lost tooth tissues, depending on the size and location of the defect. Among the most frequently employed materials are ceramics and composites. Ceramic materials are typically utilized for extensive defects requiring prosthetic treatment, while chemically cured and light-cured composites are preferred for direct restorations [6]. Dental composites consist of the following three primary components: a resin matrix (bisphenol A, urethane dimethacrylate), fillers (silicon oxide, quartz), and a coupling agent (vinyl silane) [7, 8, 9, 10]. Light-cured composites contain camphorquinone, a photoinitiator responsible for initiating the polymerization process under visible light. The free radical polymerization reaction is triggered upon exposure to light at a wavelength of 470 nm [11, 12, 13]. For chemically cured composites, the polymerization process is initiated by mixing two components: an organic amine and an organic peroxide [14]. The composition of the organic matrix significantly influences the resulting composite's properties, including its mechanical strength, sorption, solubility, polymerization shrinkage, abrasion resistance, color stability, and biocompatibility [15, 16, 17, 18]. Dental composites have become widely popular due to their aesthetics and favorable mechanical and functional properties, as well as their cost effectiveness. Despite these advantages, further advancements are needed, particularly in improving aesthetics and enhancing mechanical strength. Recent research efforts have concentrated on enhancing the properties of composites by either modifying the binder or developing novel fillers. For instance, [PERSON] et al. [19] explored the use of a mixture of cyclotriphosphazenes containing 4-allyl-2-methoxyphenoxy and \(\beta\)carboxoyethylphenoxy groups as a binder modifier. This approach has the potential to improve the adhesion of composite materials to dental tissues. Additionally, binder modification with aliphatic acid chlorides has been demonstrated to reduce both the viscosity and polymerization shrinkage of composite materials. Over the past decade, nanotechnology has significantly advanced the development of dental materials for reconstructing lost tooth tissues. Nanoparticles have been incorporated into polymer matrices to enhance material properties. These particles, characterized by small size (from 0.1 to 100 nm) and a high specific surface area, allow us to obtain superior mechanical, chemical, optical, and magnetic properties compared to the particles in macroscale [20, 21, 22]. Mechanical properties can be enhanced by improving the bending strength, hardness, and resistance to tribological wear. Certain nanoparticles also exhibit good electrical insulation, thermal stability, and corrosion resistance. Furthermore, particles like zirconium oxide, which possesses a high refractive index and a low absorption coefficient, can significantly enhance the optical properties of the materials. Beyond classifications based on size and shape, functional fillers also represent a distinct category, as illustrated in Figure 1.  
The current literature indicates a significant interest among researchers in the use of functional fillers in dentistry, primarily due to their applicability across various dental specialties. Commonly used fillers for modifying polymer matrices include silicon dioxide (SiO\({}_{2}\)), titanium dioxide (TiO\({}_{2}\)), and zirconium dioxide (ZrO\({}_{2}\)) [21]. A study by [PERSON] et al.