Evaluation of the repair bond strength of core materials with different structure

It was aimed to evaluate the effect of repair microtensile bond strength (μTBS), aging and applied surface pretreatments on repair μTBS of 3 flowable bulk fill core materials with different structures. In this study, 6x6x4 mm samples were prepared from bulk fill core materials (Clearfill DC Core plus, EverX Flow, SDR Flow). The samples were polymerized with LED light device (Elipar, 3M ESPE, Germany). Thermal aging process was applied to the prepared samples. According to the surface pretreatments, they were divided into 7 groups; Control, sandpaper applied to each group was applied to this group, FA; phosphoric acid, HFA; hydrofluoric acid, K; sandblasting, FA+S; phosphoric acid+silane, HFA+S; hydrofluoric acid +silane, K+S; sandblasting+silane. In addition, repair composite (3M P60) was applied without surface pretreatment or aging to determine the initial bond strength from each core material. A 4 mm high repair composite was applied to the aged and surface pretreated specimens. After the samples were kept in a humid environment at 37 °C for 24 hours, sections of approximately 1 mm² were obtained using a low speed cutting device (Micracut 125, Metkon, Bursa, Turkey) (n=15). Microtensile bond strength testing of the samples (Microtensile Tester, Bisco, IL, USA) was performed at a rate of 1 mm/min and data were recorded in MPa. Data were analyzed by 2-way ANOVA and Tukey HSD test. μGBD was statistically significantly affected by the main factors; core material structure, pre-surface treatment (p=0.00). Between surface pretreatments, K+S showed statistically higher μGBD than all groups (p<0.05), and no significant difference was observed between core materials in group K+S. The μGBD value of the EverX Flow group was generally higher when comparing the core materials (p<0.05). A statistically significant decrease in μGBD value was observed in all groups after aging compared to the initial group. Sandblasting and silane application showed the highest repair bond strength value among the surface pretreatment groups, and the EverX Flow (short fiber reinforced composite) group among the core materials.