BACKGROUND A constantly increasing number of gel fillers for aesthetic and reconstructive purposes have been introduced during the last 20 years. Most of the new ones are modified versions of the original collagen and hyaluronic acid gels. They have been reconstructed, often by adding cross-bindings to the polymer in order to obtain a more dense molecular structure, which will prolong degradation and filling effect of the gel. Other gel fillers contain particles of organic (poly-lactic acid) or inorganic (calcium hydroxylapatite) material, which have been used in human tissue for other purposes (degradable suture material and bone cement, respectively). The permanent fillers (silicone oil and polyacrylamide gel) have been used for many years, silicone mainly in the US and polyacrylamide gel in most countries outside the US and Canada. OBJECTIVE Complications occur, and they appear to be more frequent with particulated fillers, polyacrylamide gel and silicone oil. However, these complications differ in nature and depend on the filler type used. METHODS AND MATERIALS This overview presents the different gel filler types, how they interact with host tissue, and what can go wrong. The results and conclusion are based on experimental and clinical observations coupled with a search of the literature. RESULTS AND CONCLUSION Complications following homogenous hydrogels are caused by infection with bacteria, which have been inserted into the gel during injection. If not treated with relevant antibiotics (but instead steroids or large doses of NSAIDs) the bacteria form a biofilm, which gives rise to a low-grade chronic infection that is resistant to antibiotics. Complications following particulated gels and silicone oil are not known, but bacteria in a biofilm and/or endotoxins released by these is a possibility which deserves further investigations, primarily by using the fluorescence in situ hybridization (FISH) technique.

Host Tissue Interaction, Fate, and Risks of Degradable and Nondegradable Gel Fillers

The biologic behavior of a facial filler determines its advantages and disadvantages. The purpose of this article is to look at the relevant biology as part of a logical basis for making treatment decisions. Historical perspectives and biologic characteristics such as local tissue reaction (including phagocytosis and granulomatous inflammation) cross-linking, particle concentration, immunogenicity, biofilm formation, gel hardness, and collagen neogenesis are considered. Bovine collagen is the most immunogenic facial filler. Porcine and bioengineered human collagen implants have very low immunogenicity, but allergic reactions and elevations of IgG are possible. Cross-linking and concentration affect the longevity of collagen and hyaluronic acid fillers. Gel hardness affects how a hyaluronic acid filler flows through the syringe and needle. Calcium hydroxylapatite, poly-L-lactic acid, and polymethylmethacrylate fillers have been shown to stimulate collagen neogenesis. It appears that any facial filler can form a granuloma. Bacterial biofilms may play a role in the activation of quiescent granulomas. Various authors interpret the definition and significance of a granuloma differently.

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The biology of facial fillers.

With an increasing understanding of the aging process and the rapidly growing interest in minimally invasive treatments, injectable facial fillers have changed the perspective for the treatment and rejuvenation of the aging face. Other than autologous fat and certain preformed implants, the collagen family products were the only Food and Drug Administration approved soft tissue fillers. But the overwhelming interest in soft tissue fillers had led to the increase in research and development of other products including bioengineered nonpermanent implants and permanent alloplastic implants. As multiple injectable soft tissue fillers and biostimulators are continuously becoming available, it is important to understand the biophysical properties inherent in each, as these constitute the clinical characteristics of the product. This article will review the materials and properties of the currently available soft tissue fillers: hyaluronic acid, calcium hydroxylapatite, poly- l -lactic acid, polymethylmethacrylate, and autologous fat (and aspirated tissue including stem cells).

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Injectable fillers: review of material and properties.

Calcium hydroxylapatite (Radiesse) for treatment of nasolabial folds: long-term safety and efficacy results.

BACKGROUNDThe aging process is a complex interplay of intrinsic and extrinsic factors across multiple layers of the face. Accordingly, combining aesthetic interventions targeting different manifestations of aging often leads to better results than single modalities alone. However, no guidelines for

Consensus Recommendations for Combined Aesthetic Interventions in the Face Using Botulinum Toxin, Fillers, and Energy-Based Devices.

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.

Mussarratt Hussain

Papers

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