The application of hydrogen peroxide in composite repair

This study examined the influence of different surface conditioning methods on composite-to-composite microtensile bond strength. Thirty two-year old composite resin discs were randomly divided into three groups according to the different mechanical/chemical surface pretreatment tested: (1) 38% hydrogen peroxide (H₂O₂)-treatment; (2) 50-μm aluminum oxide sandblasting; (3) no treatment. Depending on the intermediate agent applied, two subgroups were created: (A) three-step adhesive system; (B) prehydrolyzed silane coupling agent + three-step adhesive system. Microtensile bond strength measurements were performed and the data were statistically analyzed with Kruskall-Wallis Analysis of Variance and Dunn's multiple range test for post hoc comparisons (p < 0.05). Failure mode was evaluated with a scanning electron microscope. Changes in composite surface topography after H₂O ₂ treatment were also investigated. Composite repair strength did not benefit from H₂O₂ treatment and adhesive application. Preliminary sandblasting significantly improved interfacial bond strength regardless of the intermediate agent applied. No changes in surface texture were produced after H₂O₂ treatment. An atypical fracture pattern was detected at the interfacial level between H₂O ₂-treated composite surfaces and the overlying adhesive and composite. H₂O₂ treatment affected the composite-to-composite repair strength: a compromised resin polymerization may occur, resulting in a poor interfacial quality and a weak bond. Sandblasting still remains a reliable technique for composite repair.