Shrinkage Stress of Resin-Based Composites in Different Compliance Conditions

Objectives: The purpose of this study was to examine and compare the shrinkage stress of 5 resin-based composites (RBCs) in different compliance conditions.
Methods: Five RBC products—SDR (Dentsply, USA), EcuSphere-Shape (DMG, Germany), Tetric N-Ceram Bulk Fill (Ivoclar Vivadent, Liechtenstein), Clearfil AP-X (Kuraray, Japan), Filtek Z350 XT (3M ESPE, USA)—were included.
Compliance of a custom-made stress measuring device (R&B Inc., Korea) was controlled by software program with a real-time feedback system. The displacement allowance of the superior part of the device was limited at a certain amount. Six sets of different compliance conditions—maximum compliance, zero compliance, and 4 different amount of displacement allowance—were used for each RBC.
For each measurement, 0.063 cm³ of material was prepared and placed on the device. During the curing time, the polymerization shrinkage stress was measured and recorded to a computer data file at every 0.1 s for 180 s. The maximum shrinkage stress were compared among the different compliance conditions, using one-way analysis of variance followed by Tukey’s post-hoc test.
Results: In all RBCs and compliance conditions, the shrinkage stress increased over time. There were significant differences in the maximum shrinkage stress among the different compliance conditions within each product (P<0.001). The lowest shrinkage stress was observed at the maximum compliance condition, and the highest stress was shown at the zero compliance condition. As the amount of compliance decreased, the shrinkage stress increased. When plotting load-compliance relationship, RBC bearing higher shrinkage stress demonstrated higher slope.
Conclusions: Within the limitations of this study, RBCs showed lower shrinkage stress in higher compliance conditions. In the aspect of material characteristics, RBCs bearing higher shrinkage stress were likely to be more sensitive in compliance-confined environment.