April 22, 2020
The word periosteum is formed by the fusion of two words: "peri" meaning "around" and "osteum" meaning "bone." As the name suggests, it is a covering of the bone that consists of connective tissue, bone cells (osteoblasts) and bone forming cells (osteogenic cells).
The periosteum consists of two layers. The outer layer consists of fibrous cells and dense connective tissue. The inner layer consists of various cells that have osteogenic potential. In between the bone itself and the periosteum lie perforating fibres known as Sharpey's fibres. In infants and children the periosteum is thick, vascular and loosely attached. This is in contrast to adults where it is thinner, less active, and firmly adherent.
Across all ages, the periosteum is always capable of differentiating into cells that can form collagen, bone, cartilage, fat and skeletal muscles. In the gingiva and the hard palate, the lining of the oral cavity is directly adhered to the periosteum. There is no layer in between. Such a firm and inelastic arrangement is called the mucoperiosteum.
There are various functions that are carried out by the periosteum. These are as follows:
Bone thickness
Periosteum plays a key role in the growth of bone in width during foetal development. During childhood, certain growth hormones, stimulate bone cells and bone forming cells. These cells perform the function of growing the bone in thickness and forming new bones.
Connective tissue attachment
Bone to muscle attachments are called tendons whereas bone to bone attachments are called ligaments. These muscles and joints are attached to the periosteum of the bone.
Vascular supply
A bone contains abundant blood vessels in the red bone marrow. These blood vessels originate from the periosteum. They carry bone forming cells in them which form various centers for the formation of new bone. The periosteum itself is supplied by periosteal arteries that originate from perforating canals in the bone. A nutrient artery supplies the inner part of the bone. Moreover, the blood to the gingiva is derived from vessels in the periosteum of alveolar bone.
Nervous Supply
Nerves accompany the blood vessels that supply the bone. The periosteum is rich in sensory nerve. There certain are pressure receptors on the periosteum that detect sensations of deformation in deeper tissues. The nerves of periosteum are sensitive to tearing or tension. This is the reason why patients of lymphomas, Hodgkins disease or aplastic anaemia feel pain during bone marrow needle biopsy.
Bone repair
Periosteum helps in repairing fracture of bone by sending fibroblasts to the fracture site. These fibroblasts lay down collagen fibres. The periosteum also develops a few of its cells to chondroblasts and sends them to the fracture site. The chondroblasts are responsible for the formation of cartilage. Hence, the collagen fibres and cartilage form a fibrocartilaginous callus which helps in bridging the fractured segments of bone.
Guided Tissue Regeneration
The osteogenic potential of the periosteum has led to its usage as connective tissue graft in Guided Tissue Regeneration (GTR). Cells derived from the periosteum are a optimal source in soft tissue engineering. This is because of their ability to perforate rapidly. Besides, they are also readily available.
These days, dentists are often asked to work on alveolar bone’s regenerative properties so that it can be used in implant dentistry and managing bone loss. Moreover, the periosteum located adjacent to the recessed gingiva is available in a quantity good enough to make it an appropriate graft. The various advantages that periosteum holds sure makes it a necessary component of the human body. However, there are times when even the periosteum gets infected or damaged.
Periostitis
In simple terms, periostitis is the inflammation of the periosteum. This condition is often associated with pain and hence is also known as periostalgia. Swelling and tenderness in the affected area is common. It is mainly a chronic condition but can also be acute. It is caused due to an infection in the bone. This can lead to formation of pus and may also lead to necrosis. Excessive physical activity can also lead to periostitis. Therefore, a structure that is invested in nearly each bone of the body needs to get the recognition that it deserves.