Resorption is the process by which the body breaks down and absorbs its own tissue. It happens in bones, teeth, and even developing embryos. In many cases, resorption is completely normal: your skeleton is constantly dissolving old bone and replacing it with new bone. But when the process outpaces rebuilding, or when it happens in places it shouldn’t, resorption becomes a medical problem. The term comes up most often in conversations about bone density, dental health, and orthodontic treatment.
How Resorption Works in Bone
Your skeleton is not a fixed structure. It’s a living tissue that continuously tears itself down and rebuilds, a cycle called bone remodeling. Specialized cells called osteoclasts dissolve old or damaged bone, while a second type of cell, osteoblasts, lay down fresh bone in its place. In a healthy adult, this cycle keeps the skeleton strong and supplies the bloodstream with calcium when levels dip too low.
The process is tightly controlled by a signaling system between these two cell types. Osteoblasts release a protein that tells osteoclast precursors to mature and start dissolving bone. At the same time, osteoblasts produce a decoy molecule called osteoprotegerin that intercepts that signal and slows osteoclast activity. The balance between these two signals determines whether bone is gained, maintained, or lost. Immune cells, including certain types of white blood cells, also help fine-tune this balance and preserve bone density under normal conditions.
When Bone Resorption Becomes a Problem
Osteoporosis develops when osteoclasts break down bone faster than osteoblasts can rebuild it. The result is lower bone density, weaker structure, and a higher risk of fractures. This imbalance accelerates naturally with aging, but several conditions push it further: postmenopausal hormone changes in women, rheumatoid arthritis, periodontal infection, overactive parathyroid glands, and even HIV and its treatments. In rheumatoid arthritis, for example, activated immune cells infiltrate the joints and flood the area with signals that ramp up osteoclast production, driving bone loss both locally and throughout the skeleton.
Parathyroid hormone plays a key role. Small dips in blood calcium trigger its release, and the hormone responds by increasing the osteoclast-activating signal while suppressing the decoy molecule that would normally hold osteoclasts in check. When a tumor or calcium absorption problem causes the parathyroid to overproduce this hormone, the result is severe skeletal deterioration.
Tooth Resorption
Resorption also affects teeth, and it’s one of the less well-known reasons people lose them. It can happen on the inside of the tooth (internal resorption, where the wall of the root canal is eaten away) or on the outside surface of the root (external resorption). Both types can be progressive and, if untreated, destroy enough tooth structure to require extraction.
The most common trigger is trauma. An injury that kills the tooth’s inner tissue and damages the root surface exposes the deeper layers to bacteria and inflammatory cells. Bacterial byproducts and tissue breakdown products then fuel aggressive, ongoing resorption of the root. On a dental X-ray, internal resorption shows up as a widened canal, while external resorption appears as irregular erosion along the root’s outer surface.
A specific type called external cervical resorption occurs near the gum line. Treatment involves cleaning out the resorption site, irrigating with alkaline solutions to neutralize the cells responsible for dissolving tissue, and filling the defect with a biocompatible material. In mild cases this stops the process entirely with no recurrence. In severe cases where the root is significantly weakened, a dentist may need to weigh whether the tooth can be saved or whether it’s at risk of fracturing.
Resorption During Orthodontic Treatment
Root resorption is a recognized side effect of braces and other orthodontic appliances. The forces used to move teeth through bone can trigger osteoclast activity at the root tips. Studies using 3D imaging find that roughly 45 to 64 percent of orthodontic patients show some degree of root shortening, though the vast majority of cases are mild. In one study, the average root shortening measured less than half a millimeter regardless of the patient’s age group, and severe resorption affected fewer than 8 percent of patients. For most people, this amount of shortening has no meaningful effect on tooth stability or longevity.
Resorption in Pregnancy and Embryonic Development
In mammals, not every implanted embryo survives. A significant percentage of implantations are lost through spontaneous embryo resorption, where the mother’s body breaks down and reabsorbs the tissue. Research in mice shows this process begins with the embryo itself undergoing programmed cell death, without any initial involvement from the mother’s cells. Once the barrier between embryonic and maternal tissue breaks down, the mother’s immune cells (primarily a type of white blood cell called neutrophils) invade, and the embryo is expelled into the uterine cavity and rapidly reabsorbed. The maternal tissue at the implantation site dissolves through a combination of cell death and immune cell activity. This is a normal biological process, not a sign of disease.
Resorbable Medical Materials
The concept of resorption extends to medical devices designed to dissolve inside the body. Resorbable (or absorbable) surgical sutures are made from materials like polyglycolide, polylactide, and polydioxanone. These threads hold a wound together while it heals, then gradually break down so they don’t need to be removed.
How fast they dissolve depends on their composition. Sutures made entirely from glycolide-based material absorb fastest. Polylactide and polydioxanone threads last the longest. In practical terms, some common suture types begin losing significant strength within 7 to 14 days in body fluids, while others maintain their strength for 21 days or more. Your surgeon chooses the material based on how long the wound needs mechanical support before it can hold itself together.
How Excessive Bone Resorption Is Treated
The most widely used medications for slowing bone resorption are a class of drugs called bisphosphonates. These molecules have a strong chemical attraction to bone mineral, so after you take them, they concentrate in your skeleton and sit in the bone matrix. When an osteoclast begins dissolving bone and encounters the drug, it absorbs it. Inside the osteoclast, the drug disrupts a key enzyme the cell needs to maintain its internal structure and survive. The osteoclast essentially disassembles itself and dies.
Newer nitrogen-containing versions of these drugs are 10 to 10,000 times more potent at blocking resorption than earlier formulations. Bisphosphonates are used for osteoporosis, bone cancers that have spread from other sites, and conditions where bone is being broken down too aggressively. Doctors can track whether treatment is working by measuring breakdown products in the blood. One common marker has a typical value around 0.28 nanograms per milliliter in healthy premenopausal women, and the goal of treatment is to bring a patient’s levels back into that reference range.