Fracture Toughness of UDMA based Dental Composites

Purpose: The objective of this study was to compare the fracture toughness of three model dental flowable composites compounded using three urethane dimethacrylate acrylates.  Methods: Three composite resin formulas were compounded 55% 0.7 µ silanted glass filler and 45% resin (w/w) where the resin components were formulated as follows: 1) urethane dimethacrylate (UDMA) (FW= 470.5) 66%, triethylene glycol dimethacrylate (TEGDMA) 34%  2) dimer acid dimethacrylate (FW = 847) 33%, UDMA 33%, TEGDMA 34% 3) Polyethylene glycol extended UDMA (FW = 1,139) 33%, UDMA 33% TEGDMA 34%.  Specimens were light cured in appropriate molds in three overlapping steps using an Spectrum 800 curing light @ 600 mW/cm². Specimens were stored in water at 37°C for 24 hours before testing. Fracture toughness (K_Ic) was assessed using single edge notch specimens (2.5mm (B) x 5 mm (W) x 25 mm; a/w=0.5) in 3-point bend (n=12). Data was analyzed with ANOVA/Tukey's at p ≤ 0.05. 

Results:

Formula	KIc (MPa m1/2)
2) UDMA + Dimer Acid	0.367 ± 0.008
3) UDMA + PEG extended	0.304 ± 0.007
1) UDMA	0.223 ± 0.006

The three formulas were statistically different (p<0.0001). Both the Dimer acid UDMA and the PEG extended UDMA oligomers increased the fracture toughness compared to the standard UDMA resin. Differences in fracture toughness between the base UDMA and the modified compounds might be attributed to the higher molecular weight of these materials. The Dimer Acid derivatized monomer is believed to perform better than the PEG extended monomer due to the differences predicted in crosslink density in the final composite. 

Conclusion: The modified UDMA resins increased the fracture toughness of a model flowable composite resin.  This study was supported by the Health Future Foundation. All materials were provided by Esstech, Kennsington PA.