Hydroxylapatite Soft-Tissue Filler Kindles an Immune Response

Calcium hydroxylapatite (CaHA), a stable soft-tissue filler used for the treatment of facial wrinkles, stimulates an immune response with lymphocytic infiltration and foreign body giant cell formation but with no evidence of new collagen formation, claims a new study.

Researchers from the Mangat-Kuy Plastic Surgery Centers (Cincinnati, OH, USA) conducted a prospective case series and histological analysis of eight patients who were each injected subdermally with 0.1 mL of calcium hydroxylapatite in the superior postauricular sulcus; two patients were lost to follow-up. Histological evaluation at 1, 6, or 18 months after injection showed that the calcium hydroxylapatite particles were surrounded by a lymphocytic infiltrate with multiple foreign body giant cells. The investigators found no evidence of new collagen formation, migration, or heterotopic bone growth. The study was published in the September/October 2008 issue of the Archives of Facial Plastic Surgery.

"Calcium hydroxylapatite possesses many of the characteristics of the ideal filler,” said co-author Allison Holzapfel, M.D. "The material is noncarcinogenic, nontoxic, easy to work with, malleable, relatively long-lasting, and somewhat removable. However, the material does cause an immunologic response, which most likely contributes to its variable resorption rate.”

Seventy percent of bone is made up of the inorganic mineral CaHA. Carbonated-calcium deficient hydroxylapatite is the main mineral of which dental enamel and dentin are comprised. Hydroxyapatite crystals are also found in the small calcifications (within the pineal gland and other structures) known as corpora arenacea or 'brain sand'. CaHA is used in many medical applications, such as dental ridge augmentation and tissue marking, as a filler material to replace amputated bone, as a coating to promote bone ingrowth into prosthetic implants, and in facial and plastic reconstructive surgery.

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