Faster-setting calcium silicate cements–composite bonding: effect of adhesive application mode

Calcium silicate cements are widely used as pulp-capping agents, liners/bases, and repair materials in vital pulp therapy and endodontic procedures. Owing to their biocompatibility and sealing ability, they are typically placed beneath definitive restorations. This study aimed to compare the micro-shear bond strength of three faster-setting (short initial setting time) calcium silicate cements to a resin composite and to determine whether bond failure is predominantly adhesive at the interface or cohesive within the cement. Sixty cylindrical specimens were prepared of three calcium silicate cements (CSCs) products White MTA Angelus, NeoMTA 2, and Biodentine. For each cement, two adhesive application protocols were tested (passive, P, and active, A: n = 10 per subgroup). The adhesive was applied to the calcium silicate cements and layer was light-cured, and a flowable resin composite was placed on the cement surface and also light-cured. After incubation at 37 °C for 24 h, the interfaces were subjected to micro-shear bond strength testing at a crosshead speed of 0.5 mm/min. Data were analyzed using one-way analysis of variance followed by Tukey’s post hoc test (α = 0.05). Failure modes were examined under a stereomicroscope. Significant differences in micro-shear bond strength (MPa) were observed among cement types (p < 0.001). Biodentine yielded higher values (BA: 4.5 ± 2.8; BP: 6.1 ± 4.1) than White MTA Angelus (AA: 1.5 ± 0.4; AP: 2.1 ± 0.4) and NeoMTA 2 (NA: 1.8 ± 0.7; NP: 1.0 ± 0.5). No significant difference was found between passive and active adhesive application within the same cement (p > 0.05). Cohesive failure predominated across all groups (> 70% of failures), and NeoMTA 2 exhibited 100% cohesive failure. The micro-shear bond strength (µSBS) between faster-setting calcium silicate cements and a flowable resin composite appeared to be limited primarily by the cement’s cohesive strength rather than at the adhesive interface. Biodentine showed higher 24-hour µSBS values compared with the other CSCs when a definitive restoration is placed in a single visit. These findings highlight the importance of considering the early µSBS and the cement’s cohesive strength when selecting a base for immediate restorative placement.