Repair potential of a laboratory-processed nano-hybrid resin composite

The purpose of this study was to compare the 24-h composite-to-composite microtensile bond strength of Gradia Forte (GF) repaired with the same or a different material after different surface treatments. Different groups were set up, in which composite blocks of GF were subjected to the following treatments: Group 1, sandblasting with 50-microm aluminum oxide and 37% phosphoric acid etching (PA); Group 2, bur roughening and etching with 37% PA; Group 3, etching with 37% PA only. In all groups, a bonding resin was used as an intermediate agent prior to layering of the repair material (Gradia Direct (GD), Gradia (G), or GF). Bond strengths were then determined and analysed statistically. Scanning electron microscopy (SEM) evaluation of substrates and bonded interfaces was also performed. Surface treatment (P < 0.001) and repair materials (P < 0.001) were factors that significantly affected repair strength, whereas their interaction (P = 0.31) had no significant effect. Group 3 showed significantly superior repair strength to Groups 1 and 2, whereas Group 2 showed significantly weaker repair strength to Groups 1 and 3. Irrespective of surface treatment, GD and G gave similar results, which were better than those obtained using GF. The lowest probability of failure was found for GD and G in Group 3, whereas the highest was found for GF in Groups 1 and 2. Premature failures occurred mainly with G and GF. No pre-testing failures were found in the sandblasting/GD subgroup. Surface-treated composites showed different textures under SEM, whereas composite-repair bonds showed comparable interfacial features.