Abstract
Objectives. To study the effect of resin matrix and maturation time (1 and 24 h) on the creepde formation of resin-composites, two of which have matrix-forming monomers that are either bis-GMA free or have an ormocer structure between the C=C groups.
Methods. 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 degrees C. Each specimen was loaded (20 MPa) for 2 h and unloaded for 2 h. The strain deformation was recorded continuously for 4 h. Statistical analysis was performed using one-way ANOVA and the Bonferroni post hoc test at a significance level of a = 0.05.
Results. The maximum creep-strain % after 1 h ranged from 1.32% to 2.50% and was reduced after 24 h post-cure to between 0.66% and 1.47%. Also, the permanent set after 1 h ranged from 0.70% up to 1.27% (Group A) and after 24 h ranged from 0.53% up to 1.20% (Group B).
Significance. 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. (C) 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.