Comonomers and Initiator system effects on the flexural strength of urethane dimethacrylate-based composites for dental restorative materials.

Objective: Evaluate the effect of two comonomers on the flexural strength of a urethane dimethacrylate (UDMA) composite and the effects of two initiator systems at two levels. The comonomers were neo decyl vinyl ester (Neo10) and hexyl methacrylate (HMA). These polymeric composites are designed as dental restorative materials. Polymerization of the composite is activated intraorally by the use of visible light in the 470 nm range.

Methods: UDMA was blended with Neo10 or HMA (9:1) and with an initiator system at 1 % or 2 % of the total mass of resin. One system was camphorquinone (CQ) and ethyl 4-dimethylaminobenzoate (4E), the other 1850 (a phosphine oxide and phenyl ketone at 1:1 by mass fraction). Resin was blended with 85.7 % mass fraction zirconia glass. Specimens (2 x 2 x 25) mm3 were made and tested in 3-point bending. An Analysis of Variance (ANOVA) was done, followed by the Tukey Test to find statistically significant differences.

Results: Differences between groups were greater than expected by chance (p < 0.001). Strength values with the same superscript letter (in the table below) were not significantly different (Tukey). Both comonomers performed poorly with the 1850 initiator at 1 % mass fraction. The HMA comonomer had the highest flexural strength, but was not statistically different from Neo10 at either level of CQ/4E. The 1850 initiator produced lower strengths than the CQ/4E system.

Strength Values
Comonomer Initiator Flexural strength (MPa) Standard deviation
Neo10  1 % 1850 100.1 c 10.1
Neo10 2 % 1850 157.0 a, b 23.5
HMA 1 % 1850 100.0 c 18.6
HMA 2 % 1850 137.0 b 27.9
Neo10 0.2 % CQ, 0.8 % 4E 163.0 a, b 21.9
Neo10 0.4 % CQ, 1.6 % 4E 166.9 a, b 11.9
HMA 0.2 % CQ, 0.8 % 4E 141.1 a, b 25.6
HMA 0.4 % CQ, 1.6 % 4E 171.6 a 17.5

The combined uncertainty of the measurements is 0.000713.

Conclusions: Our results do not differentiate between the comonomers with the CQ/4E initiator systems, but do support the hypothesis that both the initiator system and level effect flexural strength in these composites.

Support: Grant Y1-DE-1021-02, Interagency agreement NICDR/NIST.