Polymethylmethacrylate (PMMA) is a synthetic, biocompatible substance that has been used in medical industry for much of the last century. In dermal fillers, PMMA takes the form of a“microsphere” or microbead, which remains beneath the skin indefinitely to provide continued support. PMMA fillers will also contain collagen, a naturally occurring substance in the skin that provides structure and firmness. FDA approved PMMA fillers include Bellafill.
Among its different therapeutic functions, the use of polymethyl methacrylate (PMMA) for more than two decade has stood out in the replacement of the volumes lost with the aging process and filling in wrinkles and creases. It is considered a permanent biomaterial despite its reliability is widely discussed by health professionals. PMMA injection to the midface may be associated with chronic inflammation, fibrotic nodules, yellowing of the skin, and eyelid malposition. Intralesional corticosteroid injections yielded minimal or no improvement; surgical debulking achieved favorable results.
Complications of PMMA fillers may be seen early after injection or late. Delayed reactions, such as granulomas, have been observed with the use of PMMA, and are probably related to poor quality of the raw material used to manufacture the products, predisposition of each individual, collagenases, error in the implant procedure, such as variations in the size of the needle, inappropriate volume, irregular distribution and variation in the depth of the implant.
Several factors affect the type and intensity of the inflammatory reaction of the body tissues to the PMMA implantation for the purpose of aesthetic filling; Among these, the particle size distribution of the polymer microspheres is one of the most, which should be between 36-43 µm, since this seems to be the ideal size for large dermal injections, preventing phagocytosis and allowing the delivery and stabilization of this material. This size distribution is accepted and considered by reports in the medical literature, which shows that microspheres with a diameter smaller than 20 µm trigger an inflammatory granulomatous response and are proven to be phagocytosed, and microspheres larger than 50 µm would not be implanted effectively. Linked to the size of the injected microspheres, another factor that affects the stability of the implanted PMMA, and therefore, trigger the inflammatory reaction, is the amount of collagen deposition around the polymer microspheres; spheres with a diameter of 100 µm trigger the production of only 56% of fibrous connective tissue around it, while spheres with an average diameter of 40 µm promote growth of about 80% of collagen fibers. The higher the stability of the polymer, the lower the probability of dispersal and consequent exaggerated inflammatory response.
To conclude, particle size distribution is the key factor for plastic surgeons or patients seeking for removing wrinkles. The narrower of the particle size distribution, the better of the PMMA fillers.
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