## 1 Introduction  
Increasing aesthetic requirements of patients has led to the development of composite dental resins. Usually dental composites are made up from the matrix and fillers that are connected with each other by so-called silanes. Modifications of these two components in the last 20 years have increased the use of dental composites. They are a material commonly used to reconstruct lost tooth tissues using aesthetic restorations [1,2]. Composite materials are based on methacrylate compounds. Their matrix is an organic photopolymerizing resin, which consists mostly of bisphenol A-glycidyl methacrylate (Bis-GMA), triethylene glycol dimethacrylate (TEGMA), and urethane dimethacrylate (UDMA). The inorganic phase is macro-, micro-, or nanofillers, based mostly on silicon compounds [3,4]. Additionally, the composite contains photo initiators and proadhesive agents--silanes. The micro-hybrid composites contain a mixture of at least two types of \"glass\" or quartz molecules, irregular in shape and similar in diameter (from 0.2 to 3 \(\upmu\)m) and from 5 to 15% of small particles (0.04 \(\upmu\)m). In these materials, the filler constitutes 60-70% by volume, i.e., about 77-84% by weight of the composite part [5]. In order to increase the field of application, as well as to broaden the indications for the use of composite materials, their combinations with fibers such as carbon, polyaramide, polyethylene, and glass are used [6,7]. Currently, such solutions are used in periodonontology [8], endodontics [9], prosthetics [10], and orthodontics [11]. Both wholly aromatic polyamides or the shorter aromatic polyamids form aramids and stand for synthetic polyamides comprising >85% amide groups (-CO-NH-) bound directly to two aromatic rings. Such polymers are characterized as high-performance materials due to their very good mechanical strength and exceptional high thermal resistance. They are spun into fibers and used in advanced fabrics, such as sport and work protective clothing, bullet-proof armor, advanced composites in armament and aerospace industries, composites such as asbestos substitutes, and high-temperature insulation paper. The aramid structure is based on rigid aromatic amide linkage. It is responsible for the exceptional properties of these materials. Highly directional and efficient interchain hydrogen bonds are established, giving basis to materials with a high tendency to crystallize and with extremely high cohesive energy density. At the same time, they are also responsible for the insolubility of the wholly aromatic polyamides, a disadvantage that prevents the expansion of the application field of these materials, whereas the improvement of the solubility is a topic of the present research interest [12]. Aromatic polyamides are obtained in reactions that form amide bonds between aromatic rings of high thermal stability and high strength. The outstanding rigid molecular chain structure, good orientation, and organization of the crystalline structure provides high strength and low elongation of the orientation of the molecular chains. This provides high tensile strength, impact, and differentiated thermal stability for various temperature ranges for an extended time [13]. The covalent bonds in the polymer are responsible for the high strength. However, man-made polymers generally do not exhibit the corresponding potential high modulus. High modulus and strength may result from structural perfection, crystallinity, and crystalline and amorphous orientation. It is well known that the highest elastic moduli reported from linear polymers are generally much smaller than theoretical values [14]. The bending strength of a prosthetic restoration is an extremely important feature whose assessment is necessary in specific cases of prosthesis use, for example, when it is necessity to increase its resistance to fracture during a long period of use or when a prosthesis with an elongated structure is made [15]. Chewing is the main factor that causes mechanical degradation of the composite resin.