# Effect of the Silanization of Aerosil OX50 in the Properties of Light-Cured Dental Composites
## 4 Discussion  
Silicon dioxide presents three characteristic absorption bands at 1080, 800, and 450 cm\({}^{-1}\), which correspond to the vibration modes of stretching, bending, and rocking of the Si-O-Si bonds, respectively. In the IR spectra of the untreated and silanized aerosil OX50 (Figure 2a) only two of the characteristic bands of silicon dioxide are observed, since the spectrum was recorded between 4500 and 650 cm\({}^{-1}\). The highest-intensity band appears around 1100 cm\({}^{-1}\) and the least intense one at approximately 801 cm\({}^{-1}\), corresponding to the stretching and bending vibrations of the Si-O-Si bonds, respectively. The authors have verified the occurrence of silanization by the presence of a band of low intensity around 1707 cm\({}^{-1}\) in the spectrum of silanized aerosil OX50 (Figure 2a), corresponding to the vibrations of the carbonyl group present in the MPS coupling agent [23]. The low intensity of this band suggests that a very small percentage of silane is incorporated, making it almost imperceptible for this characterization technique. When the TGA curves of the unsilanized aerosil OX50 (Figure 2b) are analyzed, it is observed that the mass of the sample remains practically constant, which is due to the thermal stability of silicon dioxide. In the case of the treated aerosil OX50, the loss of 2% mass is associated with the decomposition of the MPS. In this sense, it has been reported that the physical decomposition of silane physically absorbed on the surface occurs between 50 and 150 \({}^{\circ}\)C, while the silane chemically bonded to the filler decomposes between 200 and 600 \({}^{\circ}\)C [24]. These results demonstrate the appearance of the silanization process of the filler. The authors report that nanoparticle resins are highly aesthetic and their physical and mechanical properties are superior to others, presenting less contraction during polymerization and high resistance to fracture, compression, and traction [25]. With a smaller particle size, a better finish of the restoration is achieved, which is observed in its surface texture, reducing the possibilities of biodegradation of the material. In addition, this technology has allowed the mechanical properties of the resin to be suitable for both the anterior and posterior sectors [26]. In the micrographs of aerosil OX50 (Figure 3) it can be seen that it is formed by spherical particles in agreement with [PERSON] et al. [8], suggesting that dental composites containing smaller spherical silica particles result in more uniform stress distribution and a reduction of stress at the filler-matrix interface. An increase in filler size is expected to increase the stress concentration at the filler-matrix interface, causing more susceptibility to crack nucleation in this area due to the different rigidities of organic matrix and inorganic filler, leading to lower mechanical performance, such as lower strength of the dental composites. Figure 7: (**a**) Thermogravimetric curves; (**b**) First derivative of the thermogravimetric curves of matrices and composites. According to the manufacturer's technical indications [27], aerosil OX50 is a hydrophilic fumed silica and its average particle size is 40 nm. The slight increases in the quantity and size of the agglomerates observed for the silanized aerosil OX50 (Figure 3b), as well as the small irregularities generated, have no influence on the morphology of the particles. Despite these differences in the agglomerates, it is considered that the silanization process does not alter the particle morphology. These results coincide with those obtained by other authors who suggest that the presence of the silane molecule covalently bound to the silicon oxide implies new interactions between the nanoparticles and, therefore, a new arrangement of the aggregates.