Resorption

• Resorption is a biological process where cells break down and absorb tissue, most commonly bone or tooth material.
• It is a vital part of normal physiological processes like bone remodeling and tooth development.
• There are various types, including bone resorption (e.g., surface, lacunar) and tooth resorption (e.g., internal, external).
• Causes range from physiological factors and hormonal imbalances to inflammation, trauma, and systemic diseases.
• Clinical manifestations can include bone pain, fractures, and tooth loss, depending on the affected tissue and underlying cause.

What is Resorption?

Resorption refers to the physiological or pathological process by which cells break down and assimilate tissue or substances. While it can occur in various biological contexts, it is most commonly discussed in relation to bone and dental tissues. In these instances, specialized cells actively remove mineralized tissue, which is then reabsorbed into the body.

The resorption process explained in bone involves osteoclasts, large multinucleated cells that attach to the bone surface and secrete acids and enzymes to dissolve the mineral matrix and organic components. This process is balanced by bone formation, carried out by osteoblasts, ensuring continuous bone remodeling. This dynamic equilibrium is essential for maintaining bone strength, repairing micro-damage, and regulating calcium and phosphate levels in the blood. When this balance is disrupted, either by excessive resorption or insufficient formation, it can lead to various medical conditions.

Types of Resorption

Resorption can manifest in different forms depending on the tissue involved and the underlying mechanism. While bone resorption is a primary focus, dental tissues also undergo distinct types of resorption. Understanding these variations is crucial for diagnosis and treatment.

• Bone Resorption: This is the breakdown of bone tissue by osteoclasts. It is a normal part of bone remodeling, but excessive bone resorption can lead to conditions like osteoporosis. Types include:
  • Surface Resorption: Occurs on the outer surface of bone.
  • Lacunar Resorption: Involves the formation of small pits (Howship’s lacunae) where osteoclasts have been active.
  • Internal Resorption: Less common, it originates within the bone marrow cavity.
• Tooth Resorption: This involves the loss of dental hard tissues (dentin, cementum, enamel). It can be internal or external and is often pathological.
  • Internal Resorption: Initiates within the pulp chamber or root canal.
  • External Resorption: Originates from the outer surface of the tooth root or crown.

These types of bone resorption and dental resorption highlight the diverse ways this process can impact the body, ranging from essential maintenance to destructive pathology.

Causes and Clinical Manifestations of Resorption

The resorption causes and symptoms are varied, encompassing physiological, pathological, and iatrogenic factors. In bone, physiological resorption is a continuous process of remodeling. Pathological causes often involve an imbalance where resorption outpaces formation. Key causes include hormonal imbalances, such as elevated parathyroid hormone (hyperparathyroidism) or estrogen deficiency (menopause), which significantly increase osteoclastic activity. Inflammatory conditions, like periodontitis in the oral cavity or osteomyelitis in bone, can also trigger localized resorption due to the release of cytokines that stimulate osteoclasts.

Other causes include mechanical stress or trauma, certain medications (e.g., some corticosteroids), and systemic diseases such as Paget’s disease of bone, rheumatoid arthritis, and various cancers that metastasize to bone. The clinical manifestations depend heavily on the location and extent of resorption. In bone, symptoms may include localized pain, increased risk of fractures, and skeletal deformities. For example, osteoporosis, a condition characterized by excessive bone resorption, affects approximately 1 in 3 women and 1 in 5 men over the age of 50 worldwide, often leading to debilitating fractures, according to the International Osteoporosis Foundation.

In dental contexts, resorption can lead to tooth mobility, pain, aesthetic changes, and ultimately, tooth loss. Early detection and identification of the underlying cause are critical for managing resorption and preventing further tissue damage.