Assessment of creep and compressive strength: bulk-fill versus conventional composites

Creep of composite restorations is affected by their exposure to oral fluids. This study sought to assess the effect of media (water and 75% ethanol) and time storage on creep and compressive strength of bulk-fill and conventional composites.

Twenty-five samples (4 × 6 mm) were fabricated of X-tra fil (bulk-fill) and Estelite Sigma, Grandio SO and Z250 composites (conventional) and divided into five groups (n = 5) according to the storage condition; no storage, 24 h of water storage, 24 h of ethanol storage, 30 days of water storage and 30 days of ethanol storage at 37 °C. Following dynamic creep (1-50 MPa, 0.25 Hz, 30 min, 450 cycles), compressive strength was measured.

Estelite Sigma and Z250 conventional composites showed the highest creep (0.0193 mm and 0.0178 mm, respectively) after 24 h of ethanol storage. GrandioSO had the highest creep (0.0148) after 30 days of ethanol storage (P < 0.05). No difference was noted in creep of X-tra fil when stored in different conditions (P = 0.065). Compressive strength following dynamic force application was in the following order: Z250 > GrandioSO > Estelite and X-tra fil. Storage medium had no significant effect on compressive strength. The highest compressive strength was noted in samples stored for 30 days irrespective of the storage medium.

Alcohol and water storage increased the creep of conventional composites. Creep of bulk-fill composite was not affected by the storage time or medium. Compressive strength of conventional and bulk-fill composites was not influenced by the storage medium but increased over time.