## 1 Introduction  
The loss of teeth remains relevant today, as it has a particularly negative impact on the self-esteem and quality of life of older patients. Removable dentures have emerged as a vital solution for their oral rehabilitation due to their cost-effectiveness and simplicity of design [1; 2; 3; 4]. Although the polymer polymethyl methacrylate (PMMA) has been used for decades for the fabrication of removable dentures [5; 6; 7], its potential to cause allergic reactions due to the release of residual methyl methacrylate (MMA) monomers, its mechanical impairments due to the large dimensional changes and low impact and fatigue resistance [6; 8; 9; 10], and its esthetic impairments due to low color stability have led researchers to investigate the use of nylon-based thermoplastic polymers [5; 6]. These polyamide materials offer a high degree of esthetics due to their translucent color that mirrors the natural gingiva. Their high flexibility, high impact strength and the absence of MMA in their composition show that they offer a good alternative to PMMA [5; 6; 7; 8; 11; 12; 13; 14; 15; 16; 17].  
Among other disadvantages of flexible resins, such as the low modulus of elasticity and low tensile strength [18], they can lead to a greater accumulation of microorganisms [19] and to stains on the material caused by the pigmentation of food or after prolonged use of denture cleansers [5; 13; 16; 20].  
The cleaning habits of the oral mucosa and the remaining teeth as well as denture cleaning are particularly important for the longevity of dentures and the maintenance of oral health of denture wearers as they reduce the adhesion of biofilm to both the denture and the oral tissues [21; 22; 23]. Biofilm is responsible for the development of diseases such as denture stomatitis, especially in elderly or immunocompromised patients [22; 23].  
A denture hygiene protocol can be established using mechanical methods, chemical methods or a combination of both [16; 19]. Although mechanical brushing of dentures is recognized as a simple and efficient method to remove biofilms, it should be combined with chemical methods for better disinfection [23; 24].  
In the chemical method, the denture is immersed in chemical agents for a certain period of time. Available chemical agents include sodium hypochlorite solutions and alkali peroxides in the form of effervescent tablets [5; 9; 25].  
Although chemical disinfection procedures are essential, they may alter the physical or mechanical properties of the prosthesis if repeated frequently or over a long period of time [22; 26]. In the oral cavity, dentures are exposed to constant temperature fluctuations due to the ingestion of food and beverages. Nevertheless, there is little information on the effects on flexible resins, i.e., the literature on the influence of thermal aging and disinfection on the microhardness and flexural strength of these resins is scarce [9; 17; 27; 28; 29].  
This work aims to contribute to knowledge in this field and the following research hypotheses were formulated:  
1. Does thermal aging affect the microhardness and flexural strength of resins?
2. Does the resin type influence the microhardness and flexural strength of resins after aging?
3. Do the chemical disinfection protocols affect the microhardness and flexural strength of resins?
4. Does the resin type affect the microhardness and flexural strength of resins exposed to disinfection protocols?  
This work contributes to the knowledge of the mechanical stability of flexible resins after exposure to oral biodegradation processes and the chemical challenges of frequent disinfection with denture cleansers, which ultimately determines their clinical longevity. It can also help define the disinfection protocol that dentists should recommend to their patients to perform adequate denture hygiene without compromising the mechanical properties of the dentures.