Fabrication and Characterization of Polyolefin-Based Composites as Root Filling Materials

Methods: Composite fibres of HA and PE were extruded using a single screw extruder and Strontium oxide (SrO) was added to impart adequate radiopacity desired for root canal filling materials. The composition of the composites were optimized and characterization was conducted  using Infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and scanning electron microscope (SEM). The elastic modulus and cohesive strength of composite fibres and gutta-percha were compared, dry and after 1 month storage in simulated body fluid (SBF), using a universal testing machine. The radiographic appearance and degree of the radiopacity were established using digital radiography. The polymer molar mass of composite fibres and gutta-percha was compared after 1, 2 and 5 days of immersion in Eugenol.

Results: FTIR confirmed the presence of the components PE, HA and SrO in the composite fibres. The HA/PE composites exhibited a melting point of 110.5-111.2°C. The SEM showed a homogenous distribution of filler particles in the composite fibres, the cohesive strength and elastic modulus of the silanated HA/PE composites were significantly higher than that of gutta-percha (P<0.0001) under dry and 1 month storage in SBF. The gutta-percha in Eugenol showed a significant increase in the polymer molar mass whereas the silanated HA/PE composites remained unchanged. Radiological evaluations demonstrated that silanated HA/PE fibres are sufficiently radiopaque.

Conclusions: A new endodontic filling material made of polyethylene-silanated hydroxyapatite-strontium oxide composites was produced using a melt- extrusion process. The newly developed composite material, that can also be heat sterilized less than 115°C, displayed outstanding cohesive strength, elastic modulus and stability.