Dental pulps were collected, and incubated for 30 mins at 37°C in DMEM containing 1% collagenase D (from Clostridium histolyticum; Sigma-Aldrich, Saint Louis, MO; C5138-1G), 1 U/ml dispase (ThermoFisher; 17105-041), and 1 U/ml DNase (Invitrogen, Carlsbad, CA) before cells were dissociated by trituration. The cells were dissociated to a single-cell suspension by filtering thorough 40μm nylon mesh. Cells are stained Propidium Iodide (PI) (BioLegend, San Diego, CA, USA, 421301; 1:500). PI- cells were sorted with Cell Sorter SH800Z (SONY, Tokyo, Japan). Libraries were constructed using a commercial microdroplet-based platform, Chromium Single Cell 3' v3.1 (10×Genomics) according to the manufacturer's instructions.