## 4 Discussion
[18], the presence of larger SiO\({}_{2}\)-BaO particles (180/500 nm) in concentrations up to 15% increased the ultimate tensile strength and elastic modulus. The improvement of the mechanical properties studied for the experimental adhesives containing inorganic particles was expected since the use of silanized particles would allow a chemical union between the functional group of methacrylates and the silane (y-MPS), preventing the propagation of the fracture along the matrix--load interface, increasing the cohesive and flexural strength, and the elastic modulus [18]. Also, as the elastic modulus of a polymer is associated with the elastic properties of its components, it was expectedthat the greater stiffness presented by the filler particles would lead to an increase in this property in experimental adhesives with inorganic content [36]. The dynamic mechanical analysis proves to be quite suitable for the analysis of viscoelastic materials, being used to predict the cross-link density and the heterogeneous structure of the polymer chain since the method allows recording both the elastic and viscous response [27]. In the present study, higher values of dynamic elastic modulus were observed than the static one, in agreement with other studies [37; 38], which also showed a strong correlation between these tests and was related to the high frequency of applied force since the stiffest component of the material is then stimulated [39]. The lower Tg of the EA15 is in line with its lower degree of conversion since the greater amount of unreacted monomers would be free to move at lower temperatures, causing the peak of tan \(\delta\) recorded at lower temperatures. In fact, although the cross-link density had a higher influence on the Tg of the materials, the lower degree of material conversion can determine a lower glass transition temperature, as found in a previous study [40; 41]. In addition to the positive results achieved in relation to the mechanical properties with the incorporation of inorganic particles in the experimental adhesive systems, the bond strength to dentin using these adhesives also showed an improvement regardless of the type of composite used, in agreement with previous studies [18; 20; 22; 32]. The increase in the mechanical properties of the adhesive system can improve the distribution of stresses resulting from the contraction of polymerization of the composite, which would lead to greater bond strength [23]. At the same time, a greater number of adhesive failures was observed for the groups in that the adhesive without inorganic content was used, which may be associated with the lower bond strength associated with these groups. In fact, the higher number of adhesive or cohesive failures has been explained by the lower or higher bond strength observed, respectively, in previous studies [42; 43]. The high percentage of mixed failures for all groups could indicate, as in a previous study [44], a strong union of the experimental adhesives with dentin. In the present study, the silica nanoparticles (50 nm) were not incorporated into the primer in order to ensure that an adequate hybrid layer was obtained since the primer could freely penetrate the spaces between the collagen fibrils, which are an average of 12 nm wide [45]. When the adhesive-dentin bonding interface is strong, the defects responsible for the fracture can preferentially start in the adhesive and propagate from there; the filler particles can act as obstacles for this propagation [46]. [PERSON] et al. [32] also found better bond strength for adhesives containing filler particles (150 nm) up to 15%. [PERSON] et al. [23], using smaller particles (12 nm) at a concentration of up to 0.5%, found a significant increase in bond strength. In the study by [PERSON] et al.