# Effect of the Silanization of Aerosil OX50 in the Properties of Light-Cured Dental Composites
## 4 Discussion
In the case of composites prepared with the monomeric matrix containing MPS (M1), there are significant differences between C145 and C145s and the highest value of the property corresponds to the C145s composite. The depth of cure is one of the standard properties that should be evaluated in light-cured composite resins and is an indirect measure of the polymerization efficiency, which is decisive in the behavior of composites. Uncured material can migrate into the oral environment and cause allergic reactions in some patients, as well as stimulate the growth of bacteria around the restoration [30]. The ISO 4049:2019 standard [12] requires that these materials have a curing depth greater than 1.5 mm and that the loss of uncured material must be less than 0.5 mm, that is, that the optimal curing depth is equal to or greater than 2 mm. The maximum value recommended to dentists to layer composites when performing restorations in deep cavities is 2 mm. As can be seen in Table 2, the highest values correspond to the monomeric matrices M1 and M4, (2.95 \(\pm\) 0.01) and (2.94 \(\pm\) 0.01) mm, respectively. One of the factors that explains the high depth of cure values for the monomeric mixtures is the structure of the monomers used in the preparation of the mixtures (Bis-GMA, TEEGDMA), which polymerize by the two existing methacrylate groups at their ends. Thus, a higher degree of cross-linking is achieved with a lower amount of residual double bonds, which produces a higher efficiency in polymerization. It has been reported that with thiourethane-functionalized fillers, it is possible to improve the properties of dental resins, such as the curing depth. This was attributed to the increase in refractive index provided by the presence of thiol, thiocarbamate, and aromatic groups, which minimizes the mismatch with the refractive index of the filler during polymerization and improves light penetration at depth [21]. Water sorption and solubility are parameters that must be controlled in dental materials. Both are related to the amounts of unreacted monomers and other non-polymerizable molecules, as well as to some small polymer chains that can migrate from the cure matrix into the medium. The sorption in the oral cavity can reduce the physical and mechanical properties of composites. This reduction is mainly attributed to the hydrolytic rupture of the bond between the filler and silane, which created a fissure. The sorption is then considered as a measure of the structural changes in the polymeric matrix, and the solubility is considered as an indirect measure of the toxicity of the material. The ISO 4049:2019 standard [12] refers to adequate sorption values as those that are less than or equal to 40 \(\upmu\)g/mm\({}^{3}\) and solubility values that are less than or equal to 7.5 \(\upmu\)g/mm\({}^{3}\). The highest values of these properties correspond to the monomeric matrices and slightly exceed the limit reported in the standard. In this sense, it is known that the Bis-GMA, TEEGDMA, and MPS monomers present in the organic matrix have oxygen atoms that, when interacting with the protic solvent, form hydrogen bonds with it, favoring water sorption. The statistical analysis and the subsequent multiple comparison test developed with the water sorption values showed significant differences between the C145 and C145s composites, the latter being the one with the lowest value. It should be remembered that the C145s composite is the one that contains MPS as part of the diluent and the silanized filler, a factor that contributed to the result, demonstrating the effectiveness of the treatment by both methods to improve the surface bond. No statistically significant differences were found between the monomeric matrices M1 and M4, nor between the C445 and C445s composites, so in this case there are no effects of the particle silanization on their solubility. These results are not in complete correspondence with those obtained for the depth of cure.