Mechanical Properties of Titania Nanotube-Polymer Composites

The ideal endodontic post system should possess mechanical properties similar to those of dentin, be biocompatible, aesthetic, easy to use, and radiopaque. Currently available prefabricated post systems lack one or more of the above properties. Titania nanotubes have many desirable properties including corrosion resistance, radiopacity and biocompatibility.

Objective: To evaluate dynamic Young's modulus, shear modulus and fracture toughness (FT) of experimental titania nanotube-polymer composites.

Methods: Functionalized titania nanonotubes were synthesized in our laboratory. Notchless triangular prism specimens (6 x 6 x 12 mm) were made by embedding nanotubes (2 and 6% by weight) into urethane dimethacrylate and light curing. The control was unfilled resin. Samples were soaked in deionized water at 37°C for 1 week prior to testing. FT was measured using an Instron universal testing machine at a crosshead speed of 0.1 mm/min. Dynamic Young's and shear moduli were determined using an ultrasonic method and lithium niobate piezoelectric crystals at 10 MHz resonant frequency. Statistical analysis was conducted using a one-way analysis of variance and a Tukey B rank order test.

Results: FT values ranged between 0.93 and 1.40 MPam^0.5. There was no significant difference amongst the groups (p>0.05). Dynamic Young's and shear moduli ranged from 5.8 to 7.0 GPa and 2.0 to 2.6 GPa, respectively. Values of Young's and shear moduli for 6% filled resin were significantly higher than for unfilled and 2% filled resins (p<0.05).

Conclusion: Titania nanotube-polymer composites demonstrated improved mechanical properties compared to unfilled resin. Future studies will optimize the functionalization and content of the titania nanotube filler. Nanocomposites with mechanical properties matching those of dentin may be ideal for the fabrication of endodontic posts.

This work was funded by the Natural Sciences and Engineering Research Council of Canada. C. Chan was supported by the CIHR Network for Oral Research Training and Health.