Mechanical Properties of Photo-cu-catalyzed Azide-alkyne Based Dental Composites

Objectives: To investigate a copper catalyzed azide-alkyne cycloaddition (CuAAC) photopolymerization-based composite as a potential alternative to a dimethacrylate-based dental composite restorative materials.
Methods: Hydrophilic fumed silica, OX50 (Evonik), was functionalized in an anhydrous environment with azide and alkyne moieties utilizing different loading levels from 5-50wt%. The surface coverage area was assessed using thermogravimetric analysis (TGA). The functionalized silica was incorporated into a model photopolymerizable CuAAC resin that consisted of multifunctional azide and alkyne monomers at a 1:1 molar functional group ratio as well as 1wt% CuCl₂/PMDETA and Irgacure-819 (Ciba) as the catalyst and photoinitiator, respectively.
The resin was photocured using visible light (400-500nm) at an intensity of 100-150mW/cm². The flexural modulus and strength of the CuAAC composite system was compared with a 70:30 ratio of Bisphenol A Glycidyl Methacrylate (BisGMA, Esstech):Triethylene glycol dimethacrylate (TEGDMA, Esstech) resin with methacrylate functionalized filler phase. The functional group conversions of both the CuAAC and methacrylate composite were determined using Fourier Transform Infrared Spectroscopy (FTIR).
Results: The CuAAC composite compares favorably with the dimethacrylate composite for specimens containing azide or alkyne functionalized OX50. Increasing the amount of alkyne/azide modification up to 1wt% of filler (i.e., 0.04mmol of functional groups/gm of silica) produced an enhancement in the flexural properties. The mechanical properties of the CuAAC composite were found to have a significant dependence on conversion.
Conclusions: The use of CuAAC resin-composite, which follows the step-growth polymerization mechanism, exhibits desirable mechanical properties with increased conversions, thus rendering it an attractive potential alternative to the dimethacrylate composite system.