## 1 Introduction  
Data collected by the Global Burden of Disease Study (2017) show that untreated dental caries constitute the most common health condition [1; 2]. In the European Union, dental health expenditures (EUR 90 bn) are comparable to those spent on diabetes (EUR 111 bn) and cardiovascular diseases (EUR 119 bn). Unfortunately, in most countries, dental procedures are not covered by health insurance and the payments are out-of-pocket for patients. The current global situation (high inflation, wars, and the recent COVID-19 pandemic) makes dental treatment unattainable for many people, even in more developed countries [3]. Therefore, research aimed at increasing the durability of dental restorations is very important. A more complex evaluation including artificial aging should be carried out to aid in the development of new dental restorations. Unfortunately, ISO and ADA standards do not provide a methodology for this type of testing. Standardized tests in ISO 4049:2019 and ADA No. 27 primarily address the general characterization of dental composites. The evaluation of mechanical properties is limited to determining flexural strength and diametral tensile strength after 24 h in water (37 \({}^{\circ}\)C), which should be considered as output properties (control). In studies, aging under aqueous conditions did not significantly deteriorate the characteristics of dental composites. However, it is noteworthy that the outcomes were contingent upon the duration of water immersion [4; 5]. The water sorption and solubility test included in the standards can be considered useful for a preliminary assessment of material behavior in a water environment. However, it should be noted that the sample immersion time is limited to 7 days, which is not sufficient to achieve the complete saturation of the sample. Considering the complex environment of the oral cavity, aging methods that rely solely on water immersion are insufficient for predicting the clinical effectiveness of biomaterials. Additionally, new research directions aimed at increasing the durability of dental restorations involve the use of new, often complex technologies such as polymer matrix modification (e.g., click chemistry) [6], filler modification (e.g., composite fillers with bactericidal properties), and the selection of coupling agents. In addition, another research direction attempts to develop self-healing material [7]. Considering the above aspects, our proposal assumed that dental materials should be tested under conditions of aggressive aging to accelerate the degradation of materials in vitro, which will be useful in predicting clinical effectiveness. Such methods are widely used in other industrial fields and can simulate long-term use [8]. Tests of selected basic aging methods were carried out [9]. Given that resin-based dental composites undergo hydrolysis upon interaction with OH\({}^{-}\) ions, alkaline environments characterized by elevated hydroxyl ion concentrations serve as suitable aging media for in vitro evaluations. Notably, NaOH solution has emerged as a prevalent choice for expediting aging processes in dental composite assessments [10; 11]. Additionally, exposing the materials to repeated temperature changes has a notable influence on the materials under investigation. Considering that thermal fluctuations occur approximately 20 to 50 times daily within the oral environment [12], it is imperative to take this into account during the material testing approach for appraising the service life of dental composites. Based on the obtained results [9], a complex aging protocol consisting of thermocyles and an aggressive environment, 0.1 M NaOH solution, was selected. The thermocycling process engenders the heightened plasticization and swelling of the polymer matrix, rendering it more susceptible to infiltration by NaOH, which functions as a corrosive aging medium. As a simplification of this method, thermocyles have been replaced by aging at elevated temperatures.