Method: The materials tested were: everX (EV, GC), SDR (SD, Dentsply) Tetric Evoceram Bulk Fill (TE, Ivoclar Vivadent), Venus Bulk Fill (VE, Heraeus Kulzer), x-tra base (XB, VOCO) and x-tra fil (XF, VOCO). Cylindrical specimens (n = 4 mm, d = 1 mm, l = 18 mm) were prepared and stored at 21°C for 24 h. Moreover, similar specimens consisting of a bulk fill material and a conventional composite (Prodigy, Kerr) as a surface layer were also fabricated.
A constant torque was generated at the center of a Helmholtz coil with the attachment of a Sm-Co magnet (M = 1.06x10-2Nm/A) at the end of each specimen. The torque was controlled by the current in the coil (20 and 40 mA) and the angular displacement of each specimen was recorded for 3 h. Stress was then released and recovery was recorded for 50 h.
Results: All materials tested exhibited linear viscoelastic behavior and showed statistically significant differences (p<0.05). When tested individually, EV and XF exhibited no or the least residual strain, while the rest of the materials did not fully recover. When tested as base materials, the bulk fill composites showed better behavior overall. Shear modulus ranged from 4.01 GPa to 8.23 GPa.
Conclusion: Bulk fill materials did not exhibit uniform behavior and varied in their creep resistance. Use of a surface composite improved their performance.