Síntese ,evolução estrutural e propriedades de polímeros modificados por nanocomponentes minerais para aplicação odontológica

Abstract

The polymerization shrinkage is the major restriction in the use of dentalcomposites. It can form marginal gaps and consequently infiltration, pain,secondary caries and internal stresses that can result in cusp deflection or enamel microcracks. The aim of this study was to test the hypothesis that the incorporation of a nanocomponent derived from an argilomineral - the Montmorillonite (MMT) - in a system of methacrylate monomers based on Bis-GMA and TEGDMA, could reduce the values of polymerization shrinkage, aiming a future application in thedental materials area. Other objectives of this work were to study the structural evolution of the composites, the polymerization kinetics under high and low light intensity, and the influence of the content and surface treatment of the nanoparticles on the dimensional behavior of the composites. Four types of nanoparticles, with different surface treatments, were incorporated into the resin system: MMT Cloisite 20A, MMT Cloisite 30B, MMT Cloisite Na+ modified with Ar-vinilbenziltrimetil ammonium chloride and silanized barium glass. Six differentconcentrations, varying between 0.48% e 16.39%, were used. The composites were characterized by thermogravimetric analysis (TGA), helium picnometry, X-ray diffraction (XRD), small angle X-ray scattering (SAXS), Fourier transformed infrared spectroscopy (FTIR), and scanning electronic microscopy (SEM). Comparing with the control group (pure polymer) and with the composites with barium glass, the results showed that the incorporation of the nanoparticles, in general, reduced the values of the shrinkage polymerization when the system was activated with halogen lamp. This property is probably associated with formulations in which clays intercalate/exfoliate with the organic phase, resulting innanocomposite formation, observed by XRD and SAXS. Results by FTIR showed differences in the kinetics on polymerization as a function of different light intensities. It was observed that the kinetics of polymerization affects the kinetics of intercalation. By SEM, no significant alterations were observed in the morphology and in the dimensions of particles after the polymerization of the composites. It was observed a high degree of adhesion between the clays and the organic phase. It was concluded that the type of surfactant and the value of the cation exchange capacity (CEC) of the nanoparticles can influence the capacity of XXV the clay to intercalate with the monomers and to exfoliate and, consequently, to yield different dimensional behaviors. The technology developed in this work has a potential to be applied on the formulation of new dental composite materials, that main limitation is still the shrinkage polymerization.