## 3 Results and Discussion
### Polymerization Kinetics Evaluation  
The dependence of the degree of conversion on photopolymerization time is depicted in Figure 6, and the ultimate DC (%) values gained for the tested nanocomposites are given in Table 2. According to Figure 6, the optimal curing time was 80 s when the DC approached the maximum value, while the final conversion of the synthesized dental nanocomposites fell in the range of 47%-55%, namely relatively close to the literature data for Bis-GMA/TEGDMA based composites ranging from 46.84% to 75% [17; 23; 30; 57]. It is clear that an abrupt increase of the DC was achieved within a short period time due to the auto-acceleration or gel-effect attributed to the influence of the diffusion-controlled phenomena on the termination reaction [58]. A reduction in the increasing rate of DC was detected until a curve plateau was drawn, which is ascribed to the movement restriction of macroradicals due to the presence of the developed polymer network. The relatively low experimental DC values were obtained by virtue of the high viscosity of the formed mixture and to the glass-effect described by the effect of the diffusion phenomena on the propagation reaction, which stabilized and finally determined the DC [58; 59; 60; 61]. The above data denoted the occurrence of high amounts of residual monomers in nanocomposites. A comparison between the prepared dental nanocomposite resins regarding their DC values eventually revealed the following sequence: Neat silica composite > OTMS composite > ACPS-OTMS composite > MPS-OTMS composite > ACPS composite> MPS composite. It is obvious that nanocomposites incorporating silane blends exhibited DC values within those obtained by using their starting silane constituents. Furthermore, nanocomposites containing ACPS silane and its corresponding blends yielded higher conversion than their counterpart reinforced only with pure MPS. This attitude could be explained by the fact that the ACPS molecule contains one less methyl- group in comparison with MPS, rendering it more reactive as it constrains the macroradicals movement in a lower degree due to chemical hindrance. Hence, the ACPS silane provides more available double bonds which are potentially responsible for the achievement of higher DC values. Nevertheless, the composites filled with neat silica and OTMS silanized nanoparticles presented the highest conversions. Such type of nanoparticles have been considered as non-reactive environments [52], which might contribute to the facilitation of the dimethacrylate monomer movement during the development of polymer network, thus resulting in the increase of the number of reactant double bonds. On the contrary, the composite resins loaded with the functional silanes MPS and ACPS as well as the their blends may act rather as multifunctional monomers because of their methacrylate moieties, resulting in the condensed accumulation of the latter on the surface of silica. Under these dominant conditions, the macroradicals mobility is restricted and, thus, the gelation process occurs  
Figure 5: Surface topography characteristics measured by a 3D optical profilometer after the polishing treatment of the obtained dental nanocomposite resins containing 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.  
earlier, triggering the induction of DC in comparison with the nanocomposite resins having non-functional silanes [28].