Method: Nanogels were synthesized via solution copolymerization of either isobornyl methacrylate (IBMA) and urethane dimethacrylate (UDMA) or octyl methacrylate (OTMA) and UDMA at a 70:30 molar ratio. Nanogels were dispersed at 30 wt% in BisGMA/TEGDMA containing photoinitiator. Measurements included nanogel glass transition temperature (Tg; dynamic mechanical analysis), thin-film (~100µm) reaction kinetics (near-IR spectroscopy) , oxygen inhibited layer (OIL) thickness (stereomicroscope), and flexural modulus (FM)/ strength (FS) in three-point bending. Photocured films were extracted with methylethyl ketone to assess solubility.
Result: Addition of 30 wt% OTMA/UDMA nanogel increases resin conversion by > 10% while also increasing polymerization rate significantly. Additionally, the average OIL thickness is reduced by more than 35%. It was demonstrated that an open nanogel-modified film polymerized faster than a comparable resin control laminated between glass slides. Despite no change in the OIL thickness, extractible mass loss was reduced by nearly 60% for IBMA/UDMA nanogel-based samples, which suggests well-integrated network formation with nanogel inclusion. Mechanical properties are maintained with incorporation of the higher Tg nanogel but reduced somewhat with lower Tg nanogel addition.
|
Nanogel Tg, C° |
Conversion, % |
Rate Max, %/s |
Mass loss, wt% |
OIL thickness, µm |
FM, GPa |
FS, MPa |
Control |
- |
64.8±0.7 |
2.7±0.0 |
16.2±4.0 |
35.9±3.6 |
2.5±0.1 |
96.2±11.1 |
30 wt% IBMA/UDMA |
89.0 |
61.0±0.4 |
2.4±0.0 |
7.1±4.2 |
35.8±2.5 |
2.6±0.1 |
96.0±7.4 |
30 wt% OTMA/UDMA |
25.0 |
74.9±0.9 |
3.7±0.3 |
- |
22.7±1.8 |
2.1±0.1 |
80.6±4.6 |
Conclusion: The use of reactive nanogels is known to greatly reduce polymerization shrinkage and stress in dental resins; however, this work demonstrates potential advantages of appropriately designed nanogels in terms of oxygen inhibition resistance and decreased solubility that could yield improved dental sealants.