Effect of the amount of 3-methacyloxypropyltrimethoxysilane coupling agent on physical properties of dental resin nanocomposites.

Objectives: The purpose of this study was to evaluate the effect of the amount of 3-methacryloxypropyl-trimethoxysilane (gamma-MPS) coupling agent on some physical-mechanical properties of an experimental resin composite for understanding the optimum amount of silanization.

Methods: Silica nanoparticles (Aerosil OX 50) used as filler were silanized with 5 different amounts of gamma-MPS 1.0, 2.5, 5.0, 7.5 and 10 wt% relative to silica. The silanizated silica nanoparticles were identified by FT-IR spectroscopy and thermogravimetric analysis (TGA). Then the silanized nanoparticles (60 wt%) were mixed with a Bis-GMA/TEGDMA (50/50 wt/wt) matrix. Degree of conversion of light cured composites was determined by FT-IR analysis. The static flexural strength and flexural modulus were measured using a three-point bending set up. The dynamic thermomechanical properties were determined by DMA analyzer. Sorption, solubility and volumetric change were determined after storage of composites in water or ethanol/water solution. Thermogravimetric analysis was performed in air and in nitrogen atmosphere from 50 to 800 degrees C.

Results: At lower silane amounts used (1.0, 2.5 wt%) the silane molecules must have a parallel orientation relative to the silica surface. At higher silane amounts (>2.5 wt%) silane molecules form a layer around the filler particles which now have to occupy a random, parallel and perpendicularly orientation relative to the silica surface. No significant statistic difference was found to exist between the flexural strength and flexural modulus values of composites with different silane contents. Dynamic elastic modulus E' showed a maximum value for the composite contained 5 wt% silane. The composites with the higher amounts of silane showed the lower values for the tandelta at the T(g) revealing that these composites have better interfacial adhesion between filler and matrix.

Significance: The amount of silane used for the silanization of silica particles affect the orientation of the silane molecules relative to the silica surface. This seems to affect the dynamic mechanical properties of composites.