Methods: The ultrasonic equipment comprised a pulser–receiver, transducers and an oscilloscope was used. Cements were mixed according to the manufacturers' instructions and inserted into the transparent mold. The cement specimen was put on the sample stage and light irradiated. The two-way transit time through the mixing cement disk was divided by two, in order to account for the down-and-back travel path, and then multiplied by the sonic velocity within the material. The sonic velocities of the longitudinal and shear waves were used to determine the elastic modulus. Analysis of variance and the Tukey HSD test were used.
Results: In the earliest stages of the setting process, most of the ultrasound energy was absorbed by the cements and the second echoes were relatively weak. As the cements hardened, the sound velocities increased until they reached a plateau. The mean elastic moduli of the specimens ranged from 11.1 to 13.8 GPa after 15 min, and from 14.0 to 17.0 GPa after 24 h. Significant increases in elastic moduli with time were found for all the materials tested.
Conclusion: The ultrasonic method used in this study has considerable potential for determining the setting processes of adhesive resin cements.