A novel fast-setting calcium silicate cement containing fluoride (novel-CSC) has been developed for applications in tooth crowns. The aim of this study was to assess the ability of the novel-CSC to close the experimental gaps at the dentin-cement interface. The novel-CSC was tested against Vitrebond and GC Fuji II LC. Experimental gaps of 50 or 300 μm width were created between the materials and dentin. Specimens with the 300-μm-wide gap were immersed in phosphate-buffered saline and the closed gap area was measured during 96 h. All specimens with 50 or 300 μm gap width were analyzed by scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM/EDX) to assess the morphology and chemical composition of the precipitates after 96 h immersion in phosphate-buffered saline. High-resolution micro-computed tomography (μCT) was used to evaluate the integrity and continuity of the precipitiates after 96 h and 180 d. In all novel-CSC samples, precipitates closed the gap area completely after 96 h. The SEM/EDX revealed that the globular precipitates closing the gap area were mainly composed of calcium and phosphorus. After 180 d, μCT indicated thicker precipitates compared with initial precipitates only in the novel-CSC group, whereas no precipitates were observed in resin-modified glass ionomers. Novel-CSC promoted continuous precipitation of calcium phosphate, including apatite, and closed the experimental gaps.