Purpose: This study investigated the bonding efficacy of a new so-called self-adhesive composite hybrid onto flat (FLAT) and high C-factor class-I cavity-bottom (CAVITY) dentin. Materials and Methods: The immediate and aged (50,000 thermocycles) microtensile bond strength (μTBS) to FLAT and CAVITY dentin of the experimental self-adhesive bulk-fill restorative (K-0180 ASAR pilot [ASAR-pilot], Dentsply Sirona) was compared to that of two universal adhesives applied in self-etch mode and combined with a bulk-fill composite (Prime&Bond Elect/QuiXfil [P&Be/QuiXF], Prime&Bond Active/QuiXfil [P&Ba/QuiXF], both Dentsply Sirona), two pre-conditioned materials (Activa Bioactive-Restorative [Activa], Pulpdent; Fuji II LC Improved [Fuji2LC], GC); and one bulk-fill glass-hybrid restorative (Equia Forte Fil [EquiaF], GC). Statistically significant differences were recorded using Welch's ANOVA with Games-Howell contrast (p 0.05). Results: No significant difference in immediate μTBS was recorded when the restorative materials were applied onto FLAT dentin, except for Activa_FLAT and EquiaF_FLAT. When bonded to CAVITY dentin, the significantly highest μTBS was recorded for Fuji2LC_CAVITY (layer filled), and was not significantly different only from P&Ba/QuiXF_CAVITY. Upon aging, the highest μTBS to flat dentin was achieved by ASAR-pilot_FLAT, which was not significantly different from P&Be/QuiXF_FLAT and Fuji2LC_FLAT. No significant difference between immediate and aged μTBS was recorded for ASAR-pilot when bonded onto FLAT or CAVITY dentin; the latter, however, was associated with low bond strength. Conclusion: Favorable bonding performance was found for the new self-adhesive bulk-fill composite hybrid ASAR-pilot when bonded to flat dentin. However, much lower bond strength was recorded when ASAR-pilot was bonded to high C-factor cavity-bottom dentin. Keywords: bond strength, bulk-fill, composite, dentin, durability