Microtensile bond strength of repaired Grandio composite

Methods: Composite disks were made by layering 2 mm thick increments of the nanohybrid Grandio composite shade A1 in a Teflon mold (4x8 mm). Disks were light-cured for 40s (Elipar S10, 3M ESPE) and stored (37º/7 days) in a saline solution. Specimens were randomly divided into 4 experimental groups according to the surface treatment applied. G1: composite surface was roughened with a Cimara® bur (VOCO) and an adhesive was applied (Solobond®, VOCO); G2: sandblasting with 27 µm aluminum oxide particles (Kavo Rondoflex®, Kavo Dental GmbH), and adhesive application; G3: air-abrasion with 30 µm alumina silica-coated particles (Cojet Sand®, 3M ESPE), silane (Monobond-S®, Ivoclar-Vivadent) and adhesive; G4: negative control group without any surface treatment. Afterwards, two layers of Grandio composite (shade A3.5) were packed incrementally on the treated surfaces. Repaired specimens were stored for 24 hours or 6 months in a saline solution. The cohesive bond strength of Grandio composite blocks was determined as positive control group. Sticks of 0.8 mm²were obtained from each group and µTBS test was carried out (Instron 3345). The failure mode was evaluated and representative failures were observed under SEM. Data were analyzed by two-way ANOVA and SNK (p<0.05).

Results: Surface treatment influenced bond strength results when repairing Grandio composite whereas the storage time did not. µTBS means (standard deviations) in MPa obtained for each experimental group are shown in the table. Similar letters mean no statistically differences among groups at 24 hours and similar numbers mean no statistically differences among groups at 6 months.

Conclusion: All surface treatments tested increased the bond strength of repaired Grandio composite. However, none of them achieved the cohesive bond strength of the positive control group.