Silane content influences physicochemical properties in nanostructured model composites.

Objective: To determine the effect of organosilane content on the physicochemical properties of model composites formulated with nano-sized fillers.

Methods: Model composites were formulated with dimethacrylate-based monomers, a photoinitiator/co-initiator system and silicon dioxide nano-sized fillers treated with different amounts of 3-methacryloxypropyltrimethoxysilane (MPTS): 1.0 (G), 2.0 (G), 5.0 (G), 7.5 (G) and 10 (G) wt.% relative to SiO. Non-silanized fillers (G) were used in the control group. Degree of conversion (DC) was assessed by Fourier-transformed infrared spectroscopy (ATR-FTIR). Knoop hardness (KHN) and elastic modulus were determined before and after water storage for 4 months. Water sorption (Wsp) and solubility (Wsl) were calculated by successive mass determinations in analytical balance. Surface gloss and roughness were characterized before and after toothbrushing simulation.

Results: With the exception of those fillers treated with 1% MPTS, DC was not dependent on the silane content. Within the silanized groups, G showed the lowest initial and final KHN, without statistical difference from G. The elastic modulus was not affected by the silane content, regardless of the storage condition, but those groups formulated with at least 5% silane presented improved values after storage. Silane content did not affect the WSl, but affected Wsp, in which those groups formulated with at least 2 wt.% of MPTS produced a more resistant material than G. The use of treated particles with at least 2 wt.% of silane was able to produce materials that did not change their gloss after the brushing process. Additionally, these materials presented lower surface roughness than G after the brushing process (p < 0.05).

Significance: The concentration of MPTS affected the physicochemical properties of nano-filled composites. Therefore, 2 wt.% of silane was the optimized quantity to produce materials resistant to degradation, both in bulk and surface properties.