In earlier work we showed that Bis-GMA type resin composites, filled with non-agglomerated SiO₂ nanoparticles, have increased maximum filler loading and greater fracture resistance compared to traditional Aerosil® SiO₂ composites (IADR abst. 492, 2002). These properties were found to increase flexure strength and modulus in a Bis-GMA resin (AADR abst. 458, 2003). Objective: Non-agglomerated SiO₂ nanoparticles were investigated to determine their potential for preparing highly filled, homogeneous “microfiller” type composites based on low cure shrinkage liquid crystal (LC) diacrylate monomers, which were described earlier (AADR abst. 1978, 2002). Methods: 50-100nm SiO₂ was made by an NH₃-hydrolysis (Stöber) process, treated with g-methacryloxypropyl-trimethoxysilane and combined with photoinitiated LC-monomer (C6-LC) and Bis-GMA/TEGDMA/Bis-EMA (GTE) blends. C6-LC and GTE were combined with SiO₂ to the maximum wt% loading attainable for each. Flexural strength, modulus (E') and strain at break (e) were determined in 3-point bending on 2x2x20 mm specimens cured 3x60 sec on each side with a 400 mW/cm² quartz-tungsten blue light curing lamp (Optilux 401, Demetron). Results: Maximum nanofiller loading was 55wt% for C6-LC and 59wt% for GTE. Respectively, flexure strength = 17±3 & 33±6MPa, E' = 1.3±0.3 & 6.7±0.7GPa, and e = 19±2 & 6±2 microns. All parameters were different between groups at p<0.05. Conclusions: The homogeneous dispersion possible with these nanoparticles is not sufficient to offset the lower modulus and greater flexibility of the C6-liquid crystal monomer resin. To overcome this problem, improved surface treatment, increased crosslinking and loading with additional filler in the 0.4-1.0 micron range, will be investigated in future work. Supported by NIH/NIDCR grant P01-DE11688

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