TEM Analysis of Nanoparticle Dispersion in a Novel Endodontic Polymer

Objectives: Polymer nanocomposites(PNCs) are a new class of materials consisting of nanoparticles at very small quantities dispersed within a polymer matrix. The extent of nanoparticle dispersion in the matrix is an important property. Depending on several factors such as the type of nanomaterial, the interaction between the nanoparticle and the matrix and the physical methods used for dispersion, the nanoparticle may be exfoliated (ie. fully dispersed at a nano-scale), intercalated (partially dispersed), or remain aggregated. Exfoliated nanocomposite usually results in substantially enhanced physical properties; dimensional stability, stiffness, mechanical and thermal properties and improved drug elution characteristics. This study investigates the use of PNCs as potentially useful materials in Endodontic surgery and to determine qualitatively the degree of dispersion of various nanoparticles namely, organoclays(OC), carbon nanotubes(CNT), and Graphene in a dental monomer matrix using Transmission Electron Microscopy.

Methods: Nanoparticles were mixed with Bis-GMA/TEGDMA/HEMA monomer resins to study the degree of dispersion (intercalation or exfoliation). Samples were photo-polymerized and sectioned by ultra-microtome. Nanoparticle dispersion in samples was examined by TEM.

Results: TEM micrographs reveal that smaller mass fractions of OC (0.5% and 1.0%) in the Bis-GMA/TEGDMA/HEMA system (40/40/20 mass ratio) demonstrated a high degree of exfoliation. When larger mass fractions of OC were used, these resulted in partially intercalated/exfoliated nanocomposites. Studies with CNT and Graphene also showed a homogenous dispersion of nanoparticles.

Conclusions: From the TEM studies, it can be observed that OC particles at lower loading appear to be highly exfoliated in the polymer matrix. Good dispersion has also been achieved using carbon nanotubes and graphene. However, other quantitative analytical techniques will have to be used to completely quantify the degree of dispersion of the nanomaterials. Future studies will also examine the role of the nanoparticles in improving bulk physical properties and drug-elution characteristics of the retrograde filling materials.