Embryonic and postnatal macrophages are necessary for proper tooth development and homeostasis

The role of macrophages in teeth, beyond their function in innate immunity, remains unexplored. This study demonstrates that macrophages populate dental tissues during early development and increase in number during pre-eruptive stages postnatally. In continuously growing teeth, they are associated with epithelial and mesenchymal stem cell niches throughout lifetime. To investigate their role in development, we genetically disrupt macrophage migration using neural-crest specific Wnt1^Cre/Csf1^fl/fl and general Csf1R knockout mouse models. This results in abnormal dentin and enamel deposition, eruption defects, early tooth mispatterning, and impaired osteogenesis. Notably, the phenotype is partially rescued via bone marrow transplantation. In addition, the short-term pharmacological depletion of macrophages in wildtype adult mice causes striking disintegration of both dentin and enamel in the apical part of continuously-growing teeth, which is restored after withdrawal of clodronate. Following treatment, macrophages rapidly repopulate dental tissue and the presence of M2 reparative state phenotype is observed by single-cell RNA-seq analysis. Overall, our findings reveal essential role of macrophages in the dental development and patterning of both mesenchymal and epithelial tooth compartments. This previously unrecognized role of macrophages in teeth is reminiscent of their function in complex tissue regeneration and requires future studies to dissect precise cellular and molecular mechanisms.