Aim: This study was conducted to evaluate bulk fill and nanohybrid resin compositeat different cavity depth and after different testing periods. Materials & methods: Standardized simple box class II occluso-mesial (OM) cavities
were prepared in the selected first maxillary premolar in each quadrant. The cavity depth was adjusted to be either 2mm or 4mm in each patient. For the bulkfill composite, both the two and four-millimeters cavities, one increment of the resin composite material (Xtra-fil) was packed inside the cavity while for the nanohybrid resin composite (Grandio), the four millimeters cavities were filled incrementally by packing two increments of 2mm thickness while for the two millimeters cavities one increment (2mm) was packed to fill the cavity and light cured for 20 seconds, finished, polished and left
for the assigned time. The restored tooth was extracted atraumatically and teeth were sectioned to produce beam-shaped specimens of (1 ± 0.1 mm2). The beam specimens were attached with cyanoacrylate gel to fit the Instron Universal testing machine. The tensile load was applied at a cross-head speed of 0.5mm/minute until specimen failure
occurred. At this point the failure load in Newton was recorded. Results: Cavity depth of 2 mm showed the highest significant mean microtensile bond strength compared with that of 4 mm. Nanohybrid resin composite showed the
highest significant mean micro tensile compared with Bulkfill resin composite. The testing period of 24 hours showed highest significant mean microtensile bond strength that one tested after 3 and 6 months.
Conclusion: (1) cavity depth has an apparent influence on tensile bond strength of the tested restoratives to dentin. (2) Microtensile bond strength of the tested restorations deteriorates by aging.