Objective: Low conversion and high volume shrinkage are well known problems encountered among dental resins that contribute to poor performance of polymeric composite materials. In an effort to improve upon this, new high molecular weight urethane based monomers have been developed (FIT™ 852 from ESSTECH and FM25-80 from Septodont). The objective of this study was to compare the physical and mechanical properties of these newly developed urethane monomers when they are used as a co-monomer instead of the well known urethane dimethacrylate (UDMA), Methods: Experimental formulations were based on a resin system containing ethoxylate bis-phenolA dimethacrylate (Bis-EMA), dimer dicarbamate dimethacrylate (DDCDMA), and the new urethanes at same wt% ratio compositions. The control sample (CTR) contains UDMA, while Experimental formulation 1 (EXP1) and 2 (EXP2) contain FM25-80 and FIT™ 852 respectively. The experimental resins were light activated using camphorquinone/ethyl-4-dimethylaminobenzoate in 0.3/0.6 wt% ratio. The resin systems were tested for degree of conversion using FT-IR, volume shrinkage with a linometer, and shrinkage stress using a tensometer. Additionally, mechanical testing was carried out according to the ISO 4049. The data was analyzed statistically by one-way ANOVA and Student-Newman-Keuls test (p<0.001), Results: Results are shown in the table below. For each column, similar letters indicate no statistical differences.
| Formulation | Conversion (%) | Volume Shrinkage (%) | Stress (MPa) | Flexural Strength (MPa) | Modulus (MPa) |
| CTR | 85.8±0.2(a) | 4.68±0.17(a) | 2.20±0.12(a) | 54±5(a) | 2050±421(a) |
| EXP1 | 77.4±0.7(b) | 4.48±0.30(a) | 2.14±0.06(a) | 56±4(a) | 1707±189(a) |
| EXP2 | 82.3±0.9(c) | 5.34±0.19(b) | 2.06±0.04(a) | 51±3(a) | 1448±179(b) |
Conclusion: It can be concluded, within the conditions of this study, that replacement of UDMA by FM25-80 or FIT™ 852 leads to statistical differences in some of the physical and mechanical properties of the polymers. Septodont thanks ESSTECH for the donation of FIT™ 852 monomer.