Strength Changes of Bulk-fill Resin-Composites Aged in Food Simulating Solvents

To investigate the diametral tensile strength (DTS) of bulk-fill and conventional resin-composites after storage in food simulating solvents.

 Method:

Four bulk-fill, two nanohybrid and two microhybrid resin-composites were studied. Split stainless steel molds were used to make disks (n=15) 6 mm diameter, 2 mm thickness. Materials were placed in the mold between two glass plates and cured from both sides for 20s by LED source (1200 mW/cm²). Materials were subdivided to be stored in one of the three solvents (water, 75% ethanol/water and MEK). After 30d, materials DTS was measured at a cross head speed of 0.5mm/min. Data were analysed by ANOVA  and Turkey's test (P≤0.05).

Result:

Mean DTS of materials in water ranged from 48.7 MPa for the G-aenial universal flo (GUF) and 30.6 MPa for Ever X posterior (EXP). The three solvent systems had solubility parameters that were expressed in a log scale from 2.96 (MEK) to 3.87 (water). As these values approached that of the PMMA (2.92) the solvent power would increase. DTS was observed to decrease steadily with increasing solvent power, for all materials except GUF. The decrease was highly significant (P≤0.05) 72% (SDR) to 41% (EXP). The mode of failure remained essentially constant with a vertical (diametral) crack.     

 Conclusion:

• As the solvent solubility parameter approaches that of PMMA, the DTS of all but one material was reduced significantly.
• For the bulk-fill materials that are designed to be used as a base, their penetration by the solvents may be shielded and thus the changes observed in this study may not be of clinical importance.