Effect of thermocycling on composite-to-composite adhesion

Objectives: To evaluate the effect of thermocycling on composite-repair microtensile bond strength (µTBS) mediated by hydrophilic intermediate agents. Methods: Twenty-four, 1 month-aged (saline solution, 37°C), composite disks (8x4mm, Gradia Direct Anterior-GDA/GC) were sandblasted (50μm-Al₂O₃) and divided into four groups (N=6). A pre-hydrolyzed silane (Monobond-S/Ivoclar-Vivadent) and two silane/adhesive blends (Porcelain Bond Activator-PBA+Clearfil New Bond; PBA+Clearfil Tri-S Bond/Kuraray Inc.) were used. As a control, a hydrophobic flowable resin (Gradia Flo/GC) was applied. Each disk was incrementally repaired with GDA (8x8mm). For each group, two subgroups were created (n=3): 1. 24-h storage in saline solution (37°C); 2. thermocycling (TC, 5000 cycles/5°C-55°C). µTBS test was performed. Failure mode and interfacial quality were examined by stereo-/scanning electron-microscopy. Data were analysed with Kruskal-Wallis ANOVA and Dunn's multiple range test (p<0.05). Results: The 24-h µTBS attained by Gradia Flo and PBA+Clearfil New Bond were comparable (Table). Monobond-S recorded the lowest results. After TC PBA+Clearfil New Bond had a significant decrease in µTBS. Silane and silane/adhesive blends, as well as flowable and silane/adhesive blends were comparable following TC. After 24-h the most frequent failure mode was cohesive (flowable, silane/adhesive blends) and adhesive (silane). After TC, adhesive failures were more frequent for all intermediate agents except for silane. Flowable resin showed the lowest rate of adhesive debonding, no pre-testing failures and good interfacial quality before and after TC. Conclusions: Silane and silane/adhesive blends formed relatively stable composite-composite bonds. The use of a hydrophobic flowable resin seems more promising in preventing interfacial failure in composite repair.

Letters show differences within the same column, numbers within the same row (p<0.05).