Static and dynamic osteogenesis development during alveolar bone healing in humans: microanatomy and histomorphometric characterization.

Background: After tooth extraction the type of intramembranous ossification that take place during the alveolar bone healing could play a role in case of immediate implant placement, while the timing and the exact mechanism of bone formation is still uncertain. To clarify these aspects we evaluated and compared the bone formation during both ontogenesis of the jaws and alveolar bone healing after dental extraction. Materials and Methods: Hamster fetus of 24-days post-conception (n=3) to evaluate the intramembranous ossification process during the ontogenesis, and bone cores retrieved during implant placement from alveolar socket after three (n=5) and four (n=5) weeks of healing were used in the present study. All the specimens were fixed in 10% formalin solution buffered with PBS at pH 7.3. Following the dehydration process in an ascending series of alcohol the specimens were embedded in a glycolmethacrylate resin and, after polymerization, were sectioned using a high-precision diamond disc at about 100 µm, and ground down under running water to about 20 µm with a custom built sawing and grinding apparatus. The investigation was carried out by means of a bright field light microscope. Results: In Hamster fetus, the alveolar bone formation was related to static osteogenesis (SO) while, the basal bone facing the Meckel’s cartilage was formed by dynamic osteogenesis (DO). In human alveolar sockets, after 3 weeks, the healing appeared to follow the SO mechanism, while after 4 weeks the bone increases by a DO mechanism. Conclusions: These results demonstrate that the static bone formation (SBF) is a process not only related to skeletal development but it occurs also during the early phase of the bone healing as rapid mechanism of a great ability of space-filling. Later on, the primary bone trabeculae are adapted by dynamic bone formation (DBF).