Hydrolytic degradation of a resin composite as a function of the curing tip distance and aging

The influence of curing tip distance and storage time on the hardness of a composite was evaluated. Composite samples (Filtek Z250) were polymerized at different distances (5, 10, and 15 mm), compared with a control group (0 mm), and stored in distilled water at 37 ° C for 24 hours. The Knoop-hardness of top and bottom surfaces was assessed (25 g/30 s). Specimens were stored in distilled water for 6 and 12 months and were retested. Hardness was found to be negatively influenced by both curing tip distance and storage time. Despite similar values at 24 hours, differences in hardness values compared with the control group appeared over time. In comparing both surfaces, hardness proved to be greater at the top surface for all groups. Composites with similar initial hardness values can degrade very differently after water storage. The higher the photoactivation distance and storage time, the worse the mechanical property