Flowable composites as intermediate agents without adhesive application in resin composite repair

PURPOSE: To evaluate the effect of different intermediate resin agents on composite-to-composite microtensile bond strength (microTBS). METHODS: Composite disks (8 x 4 mm) of Gradia Direct Anterior (N = 15) and Filtek Supreme XT (N = 15), stored in a saline solution at 37 degrees C for 1 month, were sandblasted (Microetcher, 50 microm-Al2O3), cleaned (35% H3PO4), and randomly divided into five groups (N = 3) according to the intermediate agent applied. Two flowable composites (Gradia LoFlo; Filtek Supreme XT Flow) and two adhesives (Adper Scotchbond 1XT, Scotchbond Multi-Purpose) were used. As a control, no intermediate agent was applied. Each disk was incrementally repaired (8x8 mm) with the same resin as the respective substrate. By serially cutting each repaired specimen, multiple sticks of about 0.8 mm2 in cross-section were obtained and loaded in tension until failure at a cross-head speed of 0.5 mm/minute. Data were statistically analyzed. Failure mode was examined by stereo- and scanning electron-microscopy (SEM). Additional specimens were prepared to morphologically evaluate the composite-to-composite interfacial quality by SEM analysis. RESULTS: Composite substrate and intermediate agent were significant factors (Two-way ANOVA, P < 0.001). Bond strengths achieved with Gradia Direct Anterior were higher than Filtek Supreme XT. The application of flowable composites resulted in statistically superior microTBS than adhesives and control (Tukey test, P < 0.001). Failure mode was predominantly cohesive (flowable composites), cohesive/adhesive (adhesives) and adhesive (no treatment). Flowable composites and adhesives showed a good interfacial quality.