Figure 1.

Bone remodeling consists of 5 major distinct but overlapping phases. Mature osteoblasts are generated by the differentiation of mesenchymal stem cells into pre-osteoblasts. Mature osteoclasts arise from multinucleated giant cells differentiated from monocytes stimulated by two important factors, M-CSF and RANKL, followed by differentiation into pre-osteoclasts, and finally into mature osteoclasts. Phase 1 (Activation Phase): Initiating or activating bone remodeling at a specified area. Phase 2 (Resorption Phase): Osteoprogenitors and mesenchymal stem cells are simultaneously recruited while bone resorption occurs. Phase 3 (Reversal Phase): The bone remodeling process shifts from bone resorption to bone formation. Phase 4 (Formation phase): completing bone remodeling and osteoid mineralization. Phase 5 (Termination Phase): New bone replaces old bone to retain bone strength and quality. Maintaining an environment of resting bone surfaces until the next bone remodeling begins (26).