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The first mouse molar (M1) is the most common model for odontogenesis, with research particularly focused on prenatal development. However, the functional dentition forms postnatally, when the histogenesis and morphogenesis of the tooth is completed, the roots form and the tooth physically anchors into the jaw. In this work, M1 was studied from birth to eruption, assessing morphogenesis, proliferation and apoptosis, and correlating these with remodeling of the surrounding bony tissue. The M1 completed crown formation between postnatal (P) days 0-2, and the development of the tooth root was initiated at P4. From P2 until P12, cell proliferation in the dental epithelium reduced and shifted downward to the apical region of the forming root. In contrast, proliferation was maintained or increased in the mesenchymal cells of the dental follicle. At later stages, before tooth eruption (P20), cell proliferation suddenly ceased. This withdrawal from the cell cycle correlated with tooth mineralization and mesenchymal differentiation. Apoptosis was observed during all stages of M1 postnatal morphogenesis, playing a role in the removal of cells such as osteoblasts in the mandibular region and working together with osteoclasts to remodel the bone around the developing tooth. At more advanced developmental stages, apoptotic cells and bodies accumulated in the cell layers above the tooth cusps, in the path of eruption. Three-dimensional reconstruction of the developing postnatal tooth and bone indicates that the alveolar crypts form by resorption underneath the primordia, whereas the ridges form by active bone growth between the teeth and roots to form a functional complex.

Lysyl oxidase (LOX) catalyzes cross-linking of elastin and collagen, which is essential for structural integrity and function of bone tissue. The present study examined the role of Lox gene deficiency for the osteoblast phenotype in primary calvarial osteoblasts from E18.5 Lox knockout (Lox -/-) and wild type (wt) (C57 BL/6) mice. Next to Lox gene depletion, mRNA expression of Lox isoforms, LOXL1-4, was significantly down-regulated in Lox -/-bone tissue. A significant decrease of DNA synthesis of Lox -/-osteoblasts compared to wt was found. Early stages of osteoblastic apoptosis studied by Annexin-V binding as well as later stages of DNA fragmentation were not affected. However, mineral nodule formation and osteoblastic differentiation were markedly decreased, as revealed by significant down-regulation of osteoblastic markers, type I collagen, BSP and Runx2/ Cbfa1.