Photobiomodulation in Bone: Studies in vitro, in vivo, and Clinical Applications

<strong>12.1 Photobiomodulation in Bone</strong> Bone tissue comprises different types of cells, such as osteoblasts, osteocytes, and osteoclasts. Osteoblasts are cells responsible for bone matrix synthesis and bone mineralization, and for secreting type-I collagen, proteoglycan, alkaline phosphatase, and osteocalcin. Osteocytes are cells that originate from osteoblasts and became incorporated within the osteoid matrix that is formed and then calcified to become mature bone. These cells are localized deeply within the bone matrix and are well organized. Osteoclasts are the cells responsible for degrading bone and for resorption of mineralized bone during the process of bone remodeling, which is required during repair of bone tissue. In addition, the bone mass (mineralized matrix) is composed of collagen and inorganic components - such as hydroxyapatite, calcium, and phosphate - conferring tensile strength to bones and providing a well-arranged structure that can bear loads and protect against sheer stress. The process of healing bone fractures is formally separated into the following phases: • immediate response to injury, • inflammatory phase, • ossification, and • bone remodeling.