Measuring the residual stress in dental composites using a ring slitting method

Objectives The objective of this experiment was to employ the ring slitting method for the measurement of the residual stress (RS) produced in dental composite materials after polymerization. This study was designed to determine the effect of slitting and measuring time on the residual stress. Methods Rings were made in a split brass mold from three composites (Z100/3MESPE; Herculite/Kerr; Heliomolar/Ivoclar) and cured in a Triad II (Dentsply). Two points were scribed, and the rings were slit at either 1 h (Early-group) or 24 h (Delayed-group) after curing the composite. The change in the distance between the scribed points was measured using an image analyzer system at both 1 and 24 h after slitting. From the measured change, circumferential RS was calculated and statistically analyzed with ANOVA/Tukeyʹs (P<0.05). The degree of conversion of each composite at 1 and 24 h was measured with FTIR and analyzed using Studentʹs t-test (P<0.05). Results In general, the residual stress (range=0.42–2.84 MPa) was highest for Z100 and lowest for Heliomolar, but this depended upon the test conditions. The early cut (1 h slitting), 24 h measurement groups showed the highest residual stress values. Significance This study, describes a ring slitting method to measure residual stress generated in dental composites during and after curing. The stress of composite can be affected by the cutting and measurement time.