Calcium hydroxylapatite filler for facial rejuvenation: a histologic and immunohistochemical analysis.

BACKGROUND Soft-tissue augmentation using calcium hydroxylapatite (CaHA) filler has been shown to be a safe and effective filler agent. A previous study utilizing electron microscopy demonstrated deposition of collagen around filler microspheres with minimal inflammatory response. OBJECTIVE The purpose of this study was to further characterize the expression of collagen in response to injected CaHA filler material using conventional, special, and immunohistochemical (IHC) staining. MATERIALS AND METHODS Five subjects with mild to moderate nasolabial rhytids underwent a single treatment with CaHA filler. Additionally, 0.1 to 0.2 mL of the filler material was injected subdermally into the postauricular area. Six months following the treatment, all subjects underwent biopsy of the treated postauricular area. Biopsies were analyzed using hematoxylin and eosin staining, special staining with picrosirius red (PSR), and IHC staining for collagen Types I and III. RESULTS All subjects completed the study with no complications. Biopsy specimens revealed increased deposition of collagen around the filler material, which was confirmed and further characterized using PSR and IHC staining. CONCLUSION Soft tissue augmentation with CaHA filler leads to long-term deposition of new collagen surrounding filler microspheres, which may contribute to the overall improvement in the appearance of treated rhytids.