Effects of Aging on Flexural Strength of Repaired Nano Composites

Objectives: The aim of this in vitro study was to evaluate the changes in the flexural strength of nano composite restorative materials which were repaired using same materials with dentin adhesive immediately and after one year. Methods: Materials were three nano hybrid composites (Tetric EvoCeram/Ivoclar-Vivadent, Synergy D6/Coltène-Whaledent and Grandio, Voco), a nano ceramic restorative (Ceram X mono/Dentsply, DeTrey), and a nanofil composite resin (Filtek SupremeXT/3M ESPE). Samples of control group (for each material n=10, total=50) were produced in silicon mold which had a quadrangular prism form (2x2x25mm). Samples of the test group were as follows; 1 mm thick layer of each material was placed at the bottom of the silicon molds and light cured. In test group 1, for immediate repair (after 15 minutes) surfaces of the materials were etched with 35% orthophosphoric acid, rinsed, dried and then dentin adhesive (Adper Single Bond 2/3M ESPE) was applied. The molds were filled with the same restorative material and then light cured under the glass slide. Samples of test group 2 were stored as 1 mm thick layer of materials for one year in bi-distilled water at room temperature and after that the repairs were completed. The flexural strength tests were performed with an Instron Universal Testing Machine (Zwick 1474) at a cross-head speed of 1 mm/min-1, with 100 N loading forces. Data were statistically analyzed with ANOVA and Tukey's Multiple Comparison tests. Results: Flexural strengths of all materials repaired immediately are found to be higher than their control groups and one year groups (p<0.001). Flexural strengths of Grandio, Tetric EvoCeram and Synergy D6 after one year compared to that of their controls, there were no statistically significant differences (p<0.05). Conclusion: Flexural strengths of repairs of one year aged materials were lower than immediate repair of these materials.