# Static Osteogenesis versus Dynamic Osteogenesis:
## 3 SO Versus DO during Ontogeny and the Origin of Bone Tissue Diversity  
Several authors have discussed the importance of static versus dynamic osteogenesis during ontogenesis in studies on lower vertebrates and phylogenetically distant organisms as well as in bone healing. [PERSON] [29] showed that during both bone healing of alveolar cavities after dental extraction and during peri-implant bone remodeling the pattern of jaw deposition retraces the ontogenetic steps that normally occur during its formation. In a model of hamster fetuses, the author [29] showed that alveolar bone formation occurs by static osteogenesis (SO), while the basal bone facing the [PERSON]'s cartilage is deposited by dynamic osteogenesis (DO), in line with our evidence. Moreover, again in line with our results, the author reported that in human alveolar cavities the healing processes take place at the onset by SO and the thickness of the newly formed SO trabeculae by DO increases  
Figure 11: Histological sections of endochondral ossification in (**A**) osteoblastic laminae (ob) differentiated close to the remnants of calcified cartilage (asterisks), and in (**B**) bone deposition occurring through movable osteoblastic laminae forming and then compacting the primary haversian systems by dynamic osteogenesis. Figure 10: Schematic drawing showing osteocytes remaining in contact with each other by gap junctions (light blue circles), forming a functional syncytium which also stays in contact with the osteoblasts covering the bone growth surfaces (see text for further explanation). only after 4 weeks, allowing for successive remodeling processes. [PERSON]'s results [29] provided further evidence that SO is a process that is not only related to skeletal formation in membranous ossification but also occurs in the initial healing phase of the alveolar wound with the ability to quickly fill space; subsequently, the bone mass increases through DO. Confirming what we have highlighted about the collagen texture resulting from the two different types of osteogenesis, [PERSON] [29] reported that in the initial phase, SO creates a trabecular bone framework of woven bone, followed by DO, which increases the size of the trabeculae by lamellar bone deposition. With dental implants, the author later showed that the remodeling process occurred only by DO both in compact and trabecular bone. Similar aspects were emphasized by [PERSON] and [PERSON] [30] and by [PERSON] et al. [31], who underlined functional and evolutionary considerations for SO and DO in proposing a new classification of bone tissues. In fact, based solely on the distinction between tissues derived from the two different types of osteogenesis they suggested the following classification: woven bone tissue (SO-derived), parallel-fibered bone tissue (DO-derived), and complex (i.e., composite) bone tissue resulting from combined SO and DO processes. Moreover, [PERSON] and [PERSON] [30] underlined that: (1) the combination of SO-controlled rapid volume expansion and DO-controlled bone compaction characterizes the different phases of active growth; and (2) the functional relationships between the two types of osteogenesis are not only crucial at the onset of axial skeletal organogenesis, but also later, as for example in determining the diametrical growth rate of the limbs. [PERSON] and coworkers [32] tested whether the ontogenetic sequence of bone formation (suggested, in lower vertebrates, by [PERSON] et al. [7], [PERSON] et al. [10], and [PERSON] et al. [33]) is homologous and acquired also by the last common ancestor of amniotes. [PERSON]'s group [32] studied the developmental patterns of some amphibians and reptiles (pertaining to outgroups of amniotes and ectothermic amniotes), analyzing the results obtained in the context of tetrapod phylogeny.