Viscosity of Composite Cores compared at ambient and oral temperature

Objectives: This study was designed to compare quantitative differences in viscosity of five composite-core materials at room temperature and a simulated oral temperature. Methods:  The materials used were; CompCoreAF(Premier), CorePaste(Denmat), CoreRestore2(Kerr), FlouroCoreII(Dentsply/Caulk) and LuxaCore(Zenith).  A parallel plate digital plastimeter measured viscosity.  Tests were run at a room temperature of 21°C and a simulated oral temperature.  The oral temperature was simulated by placing two insulating disks approximately 5mm thick composed of EsthetX composite-resin into an oven at 39°C.  The insulating disks were placed between the test material and the plastimeter.  This warmed the test material to a higher temperature and insulated the material from the room temperature plastimeter platens.  The oven temperature was adjusted so that the insulating disks would approach approximately 37°C as they cooled.  The composite-core material was always kept at room temperature and increased in temperature as it came into contact with the insulating disks thereby simulating the warming of the material as would be expected when placed in the mouth.  Three trials of each material at each temperature were performed.  Stefan's equation was then used to calculate viscosity. Results:  All of the test materials became less viscous as they warmed to the simulated oral temperature.  CorePaste showed the greatest change in viscosity becoming 68% less viscous while FluoroCoreII changed the least becoming 3% less viscous. Conclusion:  The expected result of the test material becoming less viscous as it warmed to the simulated mouth temperature was confirmed.  The observed difference in change in viscosity between the materials may be partially due to difference in size, shape and quantity of filler particles used.