Effects of aging conditions on repair strength of resin composites

Objectives:The objectives of this study were to compare 1-the repair bond strength of aged composites after aging, 2-to evaluate the failure types and 3-to study the surface wettening properties of the intermediate adhesive layers (IMR). Methods: One commercial microhybrid (Anterior Shine™), and 3 nanohybrid composites (Grandio™, Tetric EvoCeram™ and Filtek Supreme XT™) (N=240, n=10 per group) were polymerized in the undercut cavities in polyethylene rings under myllar stripes. They were then randomly assigned to the following conditioning methods: (1) Application of the corresponding IMR of each composite (Quadrant Unibond™, Solobond Plus™, Multilink™, Adper Scotchbond 1XT™), (2) Chairside tribochemical silica-coating (30 µm CoJet)+MPS silane coupling agent (ESPE-Sil)+Visiobond™ (SC). Substrate composites were aged either in thermocycling (5-55°C, 5000x cycles), immersion in distilled water at 37°C for 6 months or in the citric acid for 1 week. The substrate-adherend combinations involved the same composite. Specimens were then subjected to shear force at the bonded adhesive interface (universal testing machine, 1mm/min). Failure types were evaluated under the light microscope. Contact angle measurements were performed for each IMR and water as the control. Results: Significant effect of the composite type (p<0.05) and conditioning method was observed (p<0.05) (2-way ANOVA, LSD tests). Thermocyling showed the most aging effect for all composites with lower results (MPa) than other aging methods tested in groups repaired with IMRs (2.8±1 - 12.5± 3.1) with 5.7% cohesive failures. SC enhanced the results (10.5±3.5 – 23±8) and showed 71.4% cohesive failures. The contact angle of silane was 0° and IMRs presented values between 0°- 38.5°. Conclusions: Either SC or IMR can be used to repair the aged composite but it should be taken into account that conditioning with SC resulted in more cohesive failures. Surface wettening properties of IMRs were better after SC for both non-aged and aged composites.