The manuscript for the first time put emphasis on the integral characteristics of apical region of mammalian developing tooth root, which we preliminarily proposed as developing apical complex（DAC） by deducing from the fact that this region features distinctive signatures for a structurally and functionally integral entity and leads the simultaneous formation of tooth root and periodontium. In this article, the histological and cellular characteristics and developmental capability of DAC were evaluated. And it was proved that DAC featured a unique“embryonic”characteristic, which not only provides a proper root/periodontal microenvironment, but also contains stem/progenitor cells capable of differentiation into multiple tooth root- and periodontium-forming cells. The sustainable development ability of DAC qualifies it as the growth center of tooth root and as a promising candidate source of cells for tooth root and periodontal regeneration.
