Some Clinically Relevant Mechanical Properties of a Newly Introduced Flowable Resin Composite

Aim: This study aimed to evaluate hardness and flexural properties of some flowable composite. Materials and methods. A specially split Teflon mold was designed (4 mm diameter × 2 mm height) for construction of 30 specimens, 10 of each tested material; Smart Dentin Replacement (SDR), Esthtic Flow (EF) and Filtek Z350X (FS). For SDR, another mold (4 mm diameter × 4 mm height) was used to make cylindrical specimens having a thickness of 4 mm to assure what is claimed by manufacturer. The specimens were measured from both sides (top and bottom) using Vickers hardness tester. For flexural characteristics, (60) rectangular bar-shaped specimens (25 mm × 2 mm × 2 mm) of the three tested resin composite materials were packed in a specially designed mold at 23±1 °C. After the 24 h water storage, half of the specimens (10 specimens of each group) were subsequently thermocycled for 3000 cycles in water baths at +5 and +55 °C, prior to testing with dwell time 30 s and the transit time was 5 s. The three-point bending test was performed with a universal testing machine. The data was collected and then statistically analyzed. Results: The top and bottom of SDR samples recorded the least mean VHN values (32.3±5.27 and 33±4.68 VHN) respectively while they were the highest values for FS (46.6±3.76 and 46.3±2.67 VHN) respectively. EF recorded intermediate values which were 38.9±2.17 for the top and 37.5±3.19 VHN for the bottom. There was statistically significant difference among VHN of the three tested materials where FS showed the highest results (46±3.76 VHN), followed by EF (37±2.17 VHN) while the least results was recorded by SDR (33±4.37 VHN). On the other hand, there was no statistically significant difference between the hardness of SDR samples measured either in 2 mm (31.50±5.05 VHN) or 4 mm (30.57±3.97 VHN) thickness. All the tested materials show insignificant flexural characteristics values either before or after thermocycling. Exceptionally, flexural strength value of SDR before thermocycling (124.8±6.573 MPa) is significantly lower than its value after thermocycling (182±18.371 MPa). Conclusions: Although SDR has the least hardness values of all the tested materials, it can satisfactorily cured in 4 mm. Thermocycling had no effect on the flexural properties of all tested materials except for those of SDR that showed a remarkable increase after thermocycling.