Development of viscoelastic stability of resin-composites incorporating novel matrices

To study the effect of resin matrix and maturation time (1 and 24 h) on the creep deformation of resin-composites, two of which have matrix-forming monomers that are either bis-GMA free or have an ormocer structure between the CC groups.

Five resin-composites: four commercial and one experimental were investigated. Six specimens were prepared for each material and were divided into two groups (n=3) according to the maturation time and condition. Group A was stored dry at room temperature for 1 h and Group B was stored for 24 h in distilled water to allow post-curing at 37°C. Each specimen was loaded (20 MPa) for 2 h and unloaded for 2 h. The strain deformation was recorded continuously for 4h. Statistical analysis was performed using one-way ANOVA and the Bonferroni post hoc test at a significance level of a=0.05.

The maximum creep-strain % after 1 h ranged from 1.32% to 2.50% and was reduced after 24h post-cure to between 0.66% and 1.47%. Also, the permanent set after 1h ranged from 0.70% up to 1.27% (Group A) and after 24 h ranged from 0.53% up to 1.20% (Group B).

Creep deformation and maximum recovery for all resin-composites decreased with time, demonstrating improvement in viscoelastic stability. However, there was no significant difference between the permanent set at different times, except for Herculite XRV Ultra. Composites with novel matrices showed comparable properties to existing bis-GMA based materials.