Tailoring Silicon Nitride Surface Chemistry for Facilitating Odontogenic Differentiation of Rat Dental Pulp Cells

Silicon nitride (Si₃N₄) can facilitate bone formation; hence, it is used as a biomaterial in orthopedics. Nevertheless, its usability for dentistry is unexplored. The aim of the present study was to investigate the effect of Si₃N₄ granules for the proliferation and odontogenic differentiation of rat dental pulp cells (rDPCs). Four different types of Si₃N₄ granules were prepared, which underwent different treatments to form pristine as-synthesized Si₃N₄, chemically treated Si₃N₄, thermally treated Si₃N₄, and Si₃N₄ sintered with 3 wt.% yttrium oxide (Y₂O₃). rDPCs were cultured on or around the Si₃N₄ granular beds. Compared with the other three types of Si₃N₄ granules, the sintered Si₃N₄ granules significantly promoted cellular attachment, upregulated the expression of odontogenic marker genes (Dentin Matrix Acidic Phosphoprotein 1 and Dentin Sialophosphoprotein) in the early phase, and enhanced the formation of mineralization nodules. Furthermore, the water contact angle of sintered Si₃N₄ was also greatly increased to 40°. These results suggest that the sintering process for Si₃N₄ with Y₂O₃ positively altered the surface properties of pristine as-synthesized Si₃N₄ granules, thereby facilitating the odontogenic differentiation of rDPCs. Thus, the introduction of a sintering treatment for Si₃N₄ granules is likely to facilitate their use in the clinical application of dentistry.