SHARPEY FIBERS: LOCATION, STRUCTURE, FUNCTION, PHYSIOLOGICAL CHANGES - ANATOMY AND PHYSIOLOGY - 2025

The Sharpey 's fibers are a set of extensions collagen forming a strong network, slightly mineralized bones firmly attached to the muscles and ligaments. They are also found on the external bone surface, where it is responsible for joining the bone to the periosteum.

These fibers have been the subject of study over the years since their function and adaptation mechanism to the bone environment were not well understood. From experiments in rodents, its structure, function and development have been better studied.

By User: Mikael Häggström - Image: The Periodontium.jpg, Public Domain, In teeth, Sharpey's fibers are the terminal branches of the periodontal ligament, which cuts its way through dental cementum to join the tooth with the periosteum of the alveolar bone of the jaws.

Sharpey's fibers were long thought to be inert and had no change during the stages of bone resorption and renewal, however there is current evidence that they are capable of varying their size and diameter to accommodate bone metabolism.

Location

Sharpey's fibers are filaments of collagen and other elements that support the skeletal system with the periosteum and the muscles and ligaments.

Bones have an outer surface, which is covered by a fibrous sheet called the periosteum. This membrane is rich in blood vessels and neurological endings; provides a good part of the external vascularization of the bone.

From Royal Society Biologist - Own work, CC BY-SA 4.0, In the 1867 edition of the journal Elements of Anatomy, Dr. William Sharpey described the existence of a complex fibro-elastic network of collagen, which pierced the bone and reached the periosteum, strongly joining these structures. These same fibers were present at the attachment of bones to muscles and ligaments.

By 1923, these branches of collagen were already known as Sharpey's fibers. That same year its presence was observed on the bony surface of the teeth.

In 1972, Dr. Cohn studied the internal composition of the tooth with an emphasis on the Sharpey fibers, describing their path from the dental cementum to the alveolar bone of the maxilla.

Sharpey's fibers are also present between the bones of the skull. Forming firm but elastic partings.

From OpenStax College (modified) - Wikimedia commons Modified from File: 904 Fibrous Joints.jpg, CC BY-SA 3.0, Most of the research that is known about Sharpey fibers has focused on studying them from those that are part of the dento-alveolar organization.

Structure

Previously, it was thought that these perforating fibers were a suspension network formed only by collagen, however, this theory is discarded since immunohistochemical studies confirmed that their structure is much more complex.

In addition, the way in which this matrix maintained its fibrous consistency, escaping the calcification caused by bone mineral elements, was striking.

Sharpey's fibers are now known to be composed of type III and VI collagen, elastin, and the glycoproteins tenascin and fibronectin.

The association of type III collagen with type VI collagen provides great stability to the Sharpey fiber network, which explains its firmness during the bone remodeling stages.

Studies carried out on the fibers located in the teeth have been able to differentiate between two types of fibers depending on their thickness: thick and fine. The thick ones measure between 8-25 µm and the thin ones less than 8 µm.

Function

Sharpey's fibers are responsible for establishing strong bonds between the bone surface and the periosteum, muscles and ligaments.

From Modified from Pbroks13 - WIKIMEDIA COMMONSFile: Bone cross-section.svg, CC BY-SA 3.0, However, it is known that in addition to this function, its complex protein structure plays a fundamental role in bone formation during the fetal stage, in increasing the resistance of bones in athletes and in bone repair in the event of trauma or injury. physiological damage.

Physiological changes of Sharpey's fibers

Fetal stage

At the time of bone formation, during gestation, the Sharpey fiber network forms around primitive bones.

Collagen fibers with elastin and tenascin and fibronectin gluproteins, organize themselves by emitting signals for cell migration and differentiation of bone cells.

When there are problems in the structure of the Sharpey fibers, pathologies of bone formation such as fibrous dysplasia are observed, in which the primitive bones do not finish calcifying properly.

Menopause

In menopausal patients, a decrease in bone mineralization occurs, resulting in loss of calcium and osteoporosis.

As for the Sharpey fibers, their organization is affected by the hormonal decrease causing their decrease in some areas of the bone.

This situation makes these areas more susceptible to mineral loss and, as a consequence, to osteoporosis.

Likewise, it is believed that the progressive muscle atrophy seen in these types of patients is partly due to the decrease in the population of Sharpey fibers that hold bone to muscle.

Fractures / physiological damage

The hormonal signals that are triggered when there is bone damage, and that activate the pathways for repair from the bone cells, also activate an adaptation mechanism in the Sharpey fibers.

Damage to the periosteum elongates the collagen in the fibers, causing them to begin to increase in diameter and size to prepare for the stage of new bone tissue formation.

Once bone remodeling is complete, the fibers return to their original size and arrangement.

Athletes

The amount of Sharpey fibers has been observed to be increased by up to 7% more in people who engage in physical activity, such as running, compared to those who are sedentary.

This increase has benefits in terms of bone strength and the proper functioning of the joints.

Old age

As time passes, Sharpey fibers, like other elements, change their protein structure, substituting type III collagen for type I collagen.

The union of type I collagen with type VI collagen does not have the same resistance effect as the original alliance, so a process of wear begins that ends in the calcification of some of the fibers of the protein network.

These calcifications make the joints not as firm as they should be. In the case of teeth, there may be movement of the teeth and even fall due to not having a stable support form.

References

1. Aaron, JE (2012). Periosteal Sharpey's fibers: a novel bone matrix regulatory system? Frontiers in endocrinology. Taken from: ncbi.nlm.nih.gov
2. Johnson, RB (2005). Synthesis of alveolar bone Sharpey's fibers during experimental tooth movement in the rat. Anat Rec A Discov Mol Cell Evol Biol. Taken from: ncbi.nlm.nih.gov
3. Taylor, DW (1971). The life and teaching of William Sharpey (1802-1880). 'Father of modern physiology' in Britain. Medical history. Taken from: ncbi.nlm.nih.gov
4. Johnson, RB; Martinez, RH (1998). Synthesis of Sharpey's fiber proteins within rodent alveolar bone. Taken from: ecmjournal.org
5. Severson, J. A; Moffett, B. C; Kokich, V; Selipsky, H. (1978). A histologic study of age changes in the adult human periodontal joint (ligament). Journal of Periodontology. Taken from: europepmc.org