This study aimed at clarifying the dynamics of bromodeoxyuridine (BrdU) label-retaining cells (LRCs) and their relationship to cell proliferation and apoptosis during pulpal healing after cavity preparation in mice.A groove-shaped cavity was prepared on the mesial cervical surface of the upper first molars, and the samples were collected at intervals of 12 hours-14 days. The demineralized paraffin sections were processed for immunohistochemistry for BrdU, nestin, and Ki-67 and apoptosis assay using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) and in situ hybridization for dentin sialophosphoprotein (Dspp).During hour 12-day 1, odontoblasts and subodontoblastic cells beneath the affected dentin showed degenerative features and TUNEL-positive reactions, and the expressions of nestin and Dspp were lost in the damaged odontoblasts. TUNEL-positive reactions were observed even in the center of the pulp tissue, whereas dense and granular LRCs remained there. On days 2-3, Ki-67-positive cells were significantly increased in number in the center of mesial dental pulp. During days 3-5, granular and few dense LRCs were committed into some (not all) nestin-positive newly differentiated odontoblast-like cells, and these differentiated cells began to express nestin and Dspp. Until day 14, tertiary dentin formation occurred next to the preexisting dentin at the mesial pulp floor in addition to the mesial coronal pulp.These results suggest that odontoblasts and subodontoblastic cells degenerate after tooth drilling, and, subsequently, dental pulp stem/progenitor cells actively proliferate and differentiate into new odontoblast-like cells.