## 3 Results and Discussion
### Surface Morphology Evaluation of the Produced Dental Nanocomposite Resins  
Figure 3a-g displays the SEM images which are representative for each dental nanocomposite obtained after the insertion of 60 wt% both neat and silane treated silica nonfillers. It is obvious that composites containing reactive silanes MPS and ACPS (Figure 3b,d), as well as their corresponding blends (Figure 3e-g), presented an extensive distribution of fillers, meaning that silica particles (bright regions) are homogeneously dispersed in the polymer network (dark regions). However, some small aggregates also well-dispersed in the cross-linked network did not seem to disrupt the overall homogeneity. There are many literature reports associating the presence of such clusters with the specific limitations interfering with the widely utilized mixing technique of hand spatulation [31, 32, 50, 51, 52]. The untreated silica and the nanoparticles with non-reactive OTMS (Figure 3a,c) were not sufficiently dispersed in the polymer matrix, leading to the formation of large clusters in  
Figure 2: (**a**) TG comparative scans reflecting the different thermal stability of the tested silica nanoparticles; (**b**) DTG curves for neat and silica nanoparticles treated with different types of organosilanes. some regions and the absence of silica fillers in other sites of the composite surface. The last observation implied that the absence of a coupling agent or even of a non-reactive silane incapable of covalent bonding to the polymer matrix may exclude the nanofillers from the cross-linked network, thus affecting the formation of an integrated matrix-filler interface. This claim was further supported by the fact that the surface elemental analysis of the composites reinforced with neat silica and OTMS modified silica revealed different Si contents along the surface of the composite (Figure 4a,b), while the Si content was almost constantly distributed for the rest of dental nanocomposite resins (Figure 4c). By comparing the photos of the dental nanocomposites loaded with the two reactive silanes MPS and ACPS (Figure 3b,d), with those of the nanocomposites having their blends (Figure 3e-g), it can be considered that fewer agglomerates were formed by using ACPS and its blends. This is possibly due to the higher reactivity and ability of the ACPS to achieve a strong matrix-filler bonding. Figure 3: _Cont._  
Figure 4: _Cont._  
Figure 3: SEM microphotos taken for dental nanocomposite resins filled with 60 wt% of: (**a**) neat silica; (**b**) MPS; (**c**) OTMS; (**d**) ACPS; (**e**) MPS-OTMS; (**f**) ACPS-OTMS; and (**g**) MPS-ACPS-treated silica nanoparticles (\(\times\)500 magnification). Table 2 accumulates the mean surface roughness data (\(S\alpha\)) of the synthesized nanocomposite resins after the polishing treatment which is an essential step in dental clinical practice. Typical topographic surface maps involving a colorimetric scale of the induced peaks (red regions) and valleys (blue regions) are also provided in Figure 5a-g. The \(S\alpha\) values obtained for each composite revealed that the different ways of the initial silica silaization may deeply influence the surface characteristics as they are arranged against the abrasive effect. Indeed, the nanocomposite resin containing 60 wt% ACPS-modified silica nanoparticles presented the smoothest surface (\(S\alpha\) = 127.41 nm, Figure 5d), while relatively irregular areas were characterized by the presence of OTMS (Figure 5c) corresponding to increased average roughness value (\(S\alpha\) = 254.26 nm). In the previous case, the high reactivity of ACPS silane favors the building of a strong matrix-filled interface which probably withstands the removal of matrix or/and fillers under the exertion of the abrasive stresses. The evaluation of surface roughness is well-considered to be crucial for dental restorative materials in terms of their aesthetics and their longevity in the oral environment.