## 4 Discussion  
In the present study, the incorporation of 7.5 or 15% of inorganic fillers in the experimental adhesive system increased some of the mechanical properties analyzed, such as elastic modulus, flexural strength, and ultimate tensile strength, and produced a slight decrease in the degree of conversion, specifically for the adhesive containing 15% of silica nanoparticles. It is speculated that this increase in the mechanical properties leads to the increase in the bond strength values to dentin, irrespective of the type of composite employed (conventional or bulk-fill). Furthermore, greater marginal gaps were observed for the adhesive system without inorganic content when used in association with the conventional composite. Based on these results, the null hypothesis of the present study was rejected. The achievement of a high degree of conversion is desirable for the longevity of the adhesive layer since it guarantees a proper conversion of the monomers that have been polymerized, consequently reducing the chances of leaching oligomers from the hybrid layer [28] and ensuring a better quality of the tooth-composite bonded interface [29]. In the present study, all experimental adhesive systems achieved similar or higher values of degree of conversion than those found in the literature for commercial [30; 31] and experimental materials [17; 19] ranging between 78% and 84%. Despite this, a statistically significant reduction was detected for the DC% of the adhesive systems containing 15% of inorganic particles compared to the control group (EA0), which agrees with [PERSON] et al. [32] who found lower DC% for adhesives with concentrations of nanoparticles of silica greater than 10%. Filler particles can be responsible for promoting light scattering, making light more difficult to reach deeper regions, especially when the filler size is half of the photoactivator light wavelength [33]. The worst performance of the adhesive system with 15% of inorganic content may be associated with greater light scattering due to a higher concentration of silica nanoparticles, negatively impacting its DC%. The addition of 7.5% did not affect the DC%, which is in agreement with a previous study [17], in which increasing the concentration of silica nanoparticles up to 10% did not change the DC%. The lower degree of conversion observed for EA15 was not able to interfere with the mechanical properties studied since all experimental adhesives containing silica nanoparticles at concentrations of 7.5 and 15% reached higher values of UTS, FS, SME, and DME than the control group; moreover, the UTS was higher for EA15 than for EA7.5. This finding agrees with previous studies that also observed that the addition of a certain amount of filler particles can promote an improvement in these mechanical properties [17; 18; 19; 20; 21]. In the studies by [PERSON] et al. [20] and [PERSON] et al. [34], the positive effect of the addition of silica nanoparticles on the flexural strength occurred only when up to 0.2% of inorganic content was present, being attributed to the good interfacial adhesion between resin matrix and fillers, which would facilitate the transfer of stresses from the matrix to the fillers, avoiding the propagation of cracks and, consequently, leading to greater mechanical strength. At higher concentrations, these authors believe that an agglomeration of the filler particles occurred, generating fragility points where the cracks would start, thus reducing the mechanical strength. In these studies, the smaller particle size (12 nm) used may have contributed to this agglomeration, which may not have occurred in the present study where larger particles (50 nm) were used. In fact, the presence of spherical silica particles of 40-120 nm in composites, as well as the good interfacial relationship between filler and matrix, were considered essential for increasing the mechanical strength of polymers [35]. In the study by [PERSON] et al.