## 4 Discussion
Regarding the effects of the disinfection processes on the resins, there is agreement that ideally, they should not change the properties of the materials. However, certain components of the chemical solutions can alter the surface properties of the resins [43]. Several studies [1; 13; 27; 29; 30; 31; 40; 41] have investigated the effects of disinfectants on the mechanical and physical properties of acrylic resins; however, there is little information on this relationship with the microhardness and flexural strength of thermoplastic resins. The present study showed that the microhardness of ProBase Hot was higher after treatment with Corega Whitening than with the other immersion methods. These results are not consistent with the literature, which states that immersion in alkaline peroxides reduces microhardness [3; 11; 13]. This can be explained by a longer immersion time in aqueous medium (15 min), which could allow a greater release of residual monomers [42; 43] and thus a lower plasticizing effect on the superficial part of the resins. [PERSON] et al. also considered the possibility of additional polymerization of the material to explain their results, which are to some extent comparable to the present study [41]. In the samples of Deflex Classic SR resin, there was a statistically significant decrease in microhardness in the Corega Oxygen Bio-Active subgroup. This is consistent with several studies in which a decrease in microhardness was observed in samples immersed in alkaline peroxides [6; 24]. In addition to their strong alkalinity, alkaline peroxides promote the release of oxygen, which damages the interchain forces of the polymers and leads to a degradation of the surface of the resins and a decrease in their microhardness [6; 9; 10; 13; 29; 30; 44; 45]. The microhardness of Deflex Classic SR resin samples immersed in Corega Whitening was also lower than that of samples immersed in Corega Oxygen Bio-Active. According to the manufacturer, there are no differences between the chemical compositions of the two types of alkaline peroxide tablets. However, it is believed that Corega Oxygen Bio-Active has a higher alkalinity because the solution contains a higher content of peroxides, which can be harmful to the surface of the resins [13]. Regarding the effect of chemical disinfection protocols on flexural strength, statistically significant differences were only observed with Deflex Supra SF resin when Corega Whitening was used. These results allow us to partially reject the third null hypothesis, which states that only Corega Whitening affects the flexural strength of Deflex Supra SF resin. This can also be explained by the fact that the test specimens were immersed for a longer period. A comparison of the resins tested showed higher values for the microhardness of the ProBase Hot specimens compared to the flexible resins. These results seem plausible considering the differences in the composition of the two resin types [8; 38]. In terms of flexural strength, the Deflex Supra SR resin showed lower values than the other resins. This can be explained by the fact that the Deflex Supra SR resin has a higher flexural strength and is more susceptible to the effects of alkaline peroxides. In addition, the difference between the two flexible resins could be due to the different nylon content of the two materials, as described by [PERSON] et al. [7] The Supra SF resin seems to be more susceptible to the plasticizing effect of chemical solutions due to its lower stiffness, thus affecting its surface more. When comparing the effects of sodium hypochlorite on the three resins, the flexural strength values changed statistically significantly. These results are consistent with the literature because although sodium hypochlorite is recommended by the American Dental Association for the disinfection of dentures, it is known to cause changes in the physical and mechanical properties of resins regardless of chemical composition [45; 46; 47; 48].