"Residual stress" can be developed during polymerization of the dental composite and it can be remained after this process was completed. The total amount of the force which applied to the composite restoration can be calculated by the sum of external and internal force. For the complete understanding of the restoration failure behavior, these two factors should be considered. In this experiment, I compared the residual stress of the recently developed nanofilled dental composite by ring slitting methods.

The composites used in this study can be categorized in two groups, one is microhybrid type-Z250, as control group, and nanofilled type-Grandio, Filtek Supreme, Ceram-X, as experimental ones. Composite ring was made and marked two reference points on the surface. Then measure the change of the distance between these two points before and after ring slitting. From the distance change, average circumferential residual stress (σθ) was calculated. In 10 minutes and 1 hour measurement groups, Filtek Supreme showed higher residual stress than Z250 and Ceram-X. In 24 hour group, Filtek showed higher stress than the other groups.

Following the result of this experiment, nanofilled composite showed similar or higher residual stress than Z250, and when comparing the Z250 and Filtek Supreme, which have quite similar matrix components, Filtek Supreme groups showed higher residual stress.