*2.1. Formation of Cell Spheroids with Gingiva-Derived Stem Cells*

Cell spheroids were made of gingiva-derived mesenchymal stem cells using the concave microwells made of silicone elastomer having 600 μm diameters (H389600, StemFIT 3D; MicroFIT, Seongnam, Korea). The number of cells loaded in each well was 1 <sup>×</sup> 106. We obtained approval from the Institutional Review Board at Seoul St Mary's Hospital, Seoul, Korea (KC20SISE0695), and informed consent was obtained from the participant. Cell spheroids made were treated with BMP-4 (ProSpec, Ness-Ziona, Israel) at 0, 2, 6, and 10 ng/mL concentrations. The morphological changes in cell spheroids were observed under an inverted microscope (Leica DM IRM, Leica Microsystems, Wetzlar, Germany). The changes in the spheroids' diameter were evaluated on Days 1, 3, 5, and 7. The diameter of the spheroids was determined as described in a previous study [18]. Figure 1 diagrams the overall design of the study.

**Figure 1.** Schematic overview of the present study's design.
