Compressive Properties of Bulk-fill Composites Versus Conventional Composites

Objectives: Bulk Fill resins are becoming more and more popular due to their simple placing technique. Nevertheless there is no enough research investigating their mechanical properties
The aim of this study was to compare their compressive strength to the conventional ones
Methods: Two sixth year dentistry students were recruited. Each student prepared 40 (3X6mm) from three different manufacturers- 3M, IVOCALR and DENTSPLY (a total of 120 samples for each).
Twenty samples were prepared from Bulk Fill in sandwich technique and 20 cylinders out of conventional composite resin in traditional preparation layering method. Out of each group 10 cylinders were examined after 24 hours of incubation in saline solution and 10 after 6 months under the same conditions. Compression test (INSTRON) was applied and the maximal compressive force at failure and stiffness, were calculated as the slope of the linear portion of the load-deflection diagram. Statistical analysis were applied on the data.

Results: Conventional composite resins showed approximately 20% higher strength and stiffness compared to Bulk Fill type of the same manufacturer (p<0.001). Significant differences between the manufactures were noticed, where consistently 3M samples displayed higher compressive properties.
Time of incubating had no effect on the mechanical properties; however different results were obtained by the two operators but it was inconsistent.

Conclusions: Conventional composite resins that were tested in this study showed superior compressive properties compared to Bulk Fill composites.