A Comparative Study of Shear Bond Strength of Bulk-Fill Composites, Packable and Flowable, as Well as Conventional Light-Curing Composite

Introduction: This study aimed to compare the Shear Bond Strength (SBS) of two bulk-fill composites versus a conventional resin composite. Materials and Methods: In this study, 60 sound extracted human premolars were selected and sectioned horizontally from one-third of the coronal crown to expose dentin using a low-speed cutting saw. The dentin bonding agent was applied to all specimens, then they were randomly divided into three groups based on their corresponding composites: Group I: Bulk-fill packable (x-tra fil, Voco, Germany); Group II: Bulk-fill flowable (x-tra base, Voco, Germany); and Group III: Conventional (Grandio, Voco, Germany). Subsequently, composite samples with a diameter of 2.5 mm and height of 4 mm were prepared. Following thermocycling (1500 cycles, 5°C -55°C), SBS testing was performed by a universal testing machine. Then, the specimens were examined for the type of fracture (adhesive, cohesive, or mixed) under a stereomicroscope at 20X magnification. Data were analyzed using 1-way ANOVA and Tukey post-hoc test in SPSS.  Results: The highest bond strength was observed in group III (52.99±6.07) and the lowest bond strength was observed in group II (49.11±4.86). There was no statistically significant difference between the packable and flowable groups in terms of SBS (P=0.19). Statistically significant differences were detected between group I and group III (P=0.005) as well as group II and group III (P=0.000). The majority of the fractures observed in all three groups were of adhesive type. Conclusion: Conventional composites produced significantly better results in comparison with bulk-fill composites as far as SBS was concerned. Therefore, it is advisable to continue the use of bulk-fill materials incrementally in dental treatment.