Hydroxyapatite (HA) is an inorganic mineral present in human bone and teeth. It plays a role in the structural strength of bone and in bone regeneration. While it occurs naturally in bone, healthcare professionals often use synthetic and natural HA when carrying out bone repair treatments.

Bone diseases and bone abnormalities are becoming more common and can cause bone loss. Bone loss can cause bones to become weak and break easily.

When bone loss occurs, the body will often replace this lost bone through bone regeneration. This process is the name for the production of new bone.

HA plays a role in natural bone regeneration. It is also a possible treatment option to help doctors stimulate bone regeneration when treating bone loss.

An X-ray of a human skeleton showing bones containing hydroxyapatite.Share on Pinterest
Tridsanu Thophet/EyeEm/Getty Images

HA is a mineral form of calcium apatite that is present in human bones. It makes up somewhere between 65% and 70% of the weight of human bone.

HA is also a type of calcium phosphate. It has low solubility, so it does not easily dissolve in water.

HA plays an important role in a person’s bones and is also important for bone regeneration. HA also plays a role in disease,

Learn more about the function and structure of bones.

HA is present in both the bones and the teeth.

Crystals of HA are present in bone in the shape of plates or needles. These crystals are around 40–60 nanometers (nm) long, 20 nm wide, and 1.5 to 5 nm thick.

The arrangements of these HA crystals can vary in number, size, and shape. These arrangements provide support for the bone’s:

  • structural stability
  • hardness
  • function

Bone damage can occur due to disease or injury, which can lead to bone loss.

These diseases and abnormalities are often due to:

Bone regeneration is the process where bone may regain its full functionality without scar formation.

HA plays an essential role in bone regeneration, of which there are two key processes:

  • Osteoinduction: This is the name for the process that induces new bone production. It involves the transformation of immature cells into preosteoblasts, which are important cells in the formation of new bone.
  • Osteoconduction: This is the term for the ability of bone-forming cells to move across a structure and replace it with new bone over time.

HA boosts bone regeneration and helps new bone form by enhancing its osteoconductivity, osteoinductivity, or both.

HA occurs naturally in bones and plays a role in bone repair. However, healthcare professionals also widely use the substance in various treatments to help aid bone repair and regeneration.

Since the 1970s, doctors have used HA-based substances clinically in bone and dental repair procedures.

Scientists combine HA with different natural or synthetic polymers or growth factors, or both. This combination imitates the natural structure of bone and stimulates bone growth to help form new bone.

Learn more about how broken bones heal.

Enamel and dentin are two of the hard tissues present in the teeth.

Enamel forms the hard outer layer of a human tooth. Dentin is the hard tissue that develops beneath the enamel. HA crystals make up around 70–80% of the weight of human dentin and enamel.

Enamel is the hardest substance in the human body and consists of large HA crystals that are 25 nm thick, 40–120 nm wide, and 160–1,000 nm long.

A person can have damaged hard tissue in their teeth due to injury or disease. Hard tissue repair is a treatment that aims to regenerate individual hard tissues.

Dentists often use synthetic and natural HA in hard tissue repair procedures.

HA is a calcium phosphate with the molecular formula Ca5(PO4)3(OH).

In its purest form, HA contains almost 40% calcium and around 18% phosphorus. This means there is a ratio of calcium to phosphorus of 1.67.

HA has a typical apatite lattice structure and forms crystals inside the body.

Learn more about calcium phosphate in bones and teeth.

Various studies are exploring the role of HA in bone growth treatments.

A 2021 animal study involving sheep used tissue-engineered HA bone (TEHB) to promote bone regeneration. They impregnated the TEHB with osteoprogenitor cells, which are stem cells that play a role in bone growth.

The study concluded that the TEHB scaffold combined with osteoprogenitor cells has the potential to be an effective bone substitute in bone regeneration treatments. The study stated that this was due to its strength and capability to promote bone regeneration.

A 2019 study stated that healthcare professionals could use mechanically-enhanced HA to create a structural support system for bone regeneration. The study adds that this mechanically-enhanced HA may work as a load-bearing bone scaffold that can support bone growth.

Another 2021 study looked at a composite material of polylactic acid-polyethylene glycol and osteogenic nano-hydroxyapatite as a possible treatment to help aid bone regeneration.

The study concluded that the composite material enabled efficient bone regeneration. It may have potential in clinical applications such as:

  • spinal fusion
  • large bone abnormalities
  • bone nonunion, which occurs when a fractured bone fails to heal and mend after an extended time

Here are some answers to common questions about HA in bone.

Does bone contain HA?

Yes, HA is an inorganic component of bone tissue. A modified form of HA is present in bone and is known as bone mineral.

The substance plays a role in structural bone strength and bone regeneration.

How much HA is in bone?

HA makes up a large proportion of human bone.

Studies state that between 65% and 70% of human bone comprises HA by weight.

Does HA stimulate bone growth?

Osteoinduction is the name for the process that stimulates bone growth.

This process involves the transformation of immature cells into preosteoblasts. These cells are important in bone growth.

HA can enhance osteoinductivity, meaning it can help stimulate bone growth.

HA is a mineral that is present in human bones and teeth. It comprises between 65% and 70% of human bone by weight.

HA plays a role in bone strength and in bone regeneration.

Medical professionals often use the substance in bone regeneration treatments, as it can stimulate bone growth.

Dentists also often use synthetic and natural HA in treatments that aim to repair the hard tissues in teeth.