title: The life cycles and biological end pathways of dermal fillers.
abstract: BACKGROUND
  There is an increased demand for soft tissue augmentation procedures. A wide range of products can provide correction through different mechanisms and it is important for clinicians to understand the biological pathways of each material. This study presents a systematic review of the pathways of commonly used fillers, with consideration of the complications associated with each.
  
  
  METHODS
  The PubMed (National Library of Medicine) database was searched for MeSH headings for different types of fillers, including trade names, between January 1, 2000, and January 1, 2013. Article titles were screened, and only studies designed to determine the mechanism of action and histopathology of complications were included.
  
  
  RESULTS
  When restricted to studies on biological mechanisms, 109 manuscripts were identified and the mechanisms of action of short-term and long-term degradable as well as permanent fillers were reviewed. Hyaluronic acid fillers, which are the most commonly used, form a fibrous capsule and induce limited de novo collagen. Poly-l-lactic acid and calcium hydroxylapatite are semipermanent fillers that provide long-term restoration of tissue volume by stimulating fibroblasts to lay down a matrix of collagen and elastic fibers. Polymethyl methacrylate is the only FDA-approved permanent implant that is held in place by encapsulation, providing a scaffold upon which the dermis can recover to its original thickness.
  
  
  CONCLUSIONS
  Soft tissue augmentation products are variable, and no single product can be considered the most effective or ideal. An understanding of biological mechanisms may help guide physicians choose the best suited product among the various options available while minimizing the occurrence of complications.
authors.affiliation: Department of Dermatology, Wake Forest School of Medicine, Winston-Salem, North Carolina, USA.
authors.forename: Christine S
authors.initials: CS
authors.lastname: Ahn
authors.forename: Babar K
authors.initials: BK
authors.lastname: Rao
mesh_terms: D001672:Biocompatible Materials / Q000009:adverse effects / Q000494:pharmacology*; D003357:Cosmetic Techniques; D017886:Durapatite / Q000009:adverse effects / Q000494:pharmacology; D005145:Face; D006801:Humans; D006820:Hyaluronic Acid / Q000009:adverse effects / Q000494:pharmacology; D007279:Injections, Subcutaneous; D019344:Lactic Acid / Q000009:adverse effects / Q000494:pharmacology; D011091:Polyesters; D011108:Polymers / Q000009:adverse effects / Q000494:pharmacology; D019904:Polymethyl Methacrylate / Q000009:adverse effects / Q000494:pharmacology; D015595:Skin Aging / Q000187:drug effects*
chemical_list: D001672:Biocompatible Materials; D011091:Polyesters; D011108:Polymers; D019344:Lactic Acid; C033616:poly(lactide); D006820:Hyaluronic Acid; D019904:Polymethyl Methacrylate; D017886:Durapatite
keywords: calcium hydroxylapatite; cosmetic procedure; hyaluronic acid; injectables; poly-l-lactic acid; polymethylacrylate