Abstract
Nanotechnology comprises a promising approach towards the update of dental materials.The present study focuses on the reinforcement ofdental nanocomposite resins with diverse organomodified montmorillonite (OMMT) nanofillers. The aim is to investigate whether the presence of functional groups in the chemical structure of the nanoclay organic modifier may virtually influence the physicochemical and/or the mechanical attitude of the dental resin nanocomposites. The structure and morphology of the prepared materials were investigated by means of wide angle X-ray diffraction and scanning electron microscopy analysis. Fourier transform infrared spectroscopy was used to determine the variation of the degree of conversion over time. Measurements of polymerization shrinkage and mechanical properties were conducted with a linear variable displacement transducer apparatus and a dynamometer, respectively. All the obtained nanocomposites revealed intercalated structures and most of them had an extensive filler distribution into the polymer matrix. Polymerization kinetics werefound to be influenced by the variance of the clay organomodifier, whilenanoclays with vinyl groups considerably increased the degree of conversion. Polymerization shrinkage was almost limited up to 50% by incorporating nanoclays. The absence of reactive groups in the OMMT structure may retain setting contraction atlow levels. An enhancement of the flexural modulus was observed, mainly by using clay nanoparticles decorated with methacrylated groups, along with a decrease in the flexural strength at a high filler loading. The overall best performance was found for the nanocomposites with OMMTs containing double bonds. The significance of the current work relies on providing novel information about chemical interactions phenomena between nanofillers and the organic matrix towards the improvement of dental restorative materials.
Highlights
Composite restorative materials were initially developed to overcome the drawbacks of silicate cements and unfilled resins based on methyl methacrylate monomer and its polymer [1]
The combination of X-ray diffraction (XRD) and Scanning electron microscopy (SEM) results confirmed the intercalation of macromolecular chains between clay platelets, while some agglomerates of clay still remained
Vinyl groups of intercalant and/or silane coupling agent promoted the better dispersion of nanofillers into the resin matrix
Summary
Composite restorative materials were initially developed to overcome the drawbacks of silicate cements and unfilled resins based on methyl methacrylate monomer and its polymer [1].aesthetic reasons and concerns associated with amalgam’s toxicity [2] established them as modern biomaterials in the dental industry. Polymers 2019, 11, 730 methacryloxypropoxy)phenylene]propane (Bis-GMA) or 1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimethylhexane (UDMA) and the co-monomer triethylene glycol dimethacrylate (TEGDMA) as viscosity controller, (b) an inorganic reinforcing filler, such as glass, quartz or fused silica, and (c) a coupling agent, such asγ-methacryloxy propyltrimethoxysilane, to enhance bonding between the filler and resin matrix. The latter contains an activator/initiator system to promote light-activated polymerization of the organic matrix and form cross-linked polymer networks [3,4,5]. Restorations based on dental composite resins are usually challenged by requirements, such as excellent mechanical properties, low wear, and water solubility or sorption, low polymerization shrinkage and marginal leakage, good biocompatibility, caries-inhibition ability and low toxicity, color matching, and stability, etc. [6,7].
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