New York City — While comprehensively covering the subject of fillers in the clinical setting at the recent meeting for the American Society for Dermatologic Surgery (ASDS), dermatologist Frederick S. Brandt, M.D., feels compelled to start with hyaluronic acids, saying, "I think that's the biggest revolution in fillers now."
Dr. Brandt, who is clinical professor of dermatology at the University of Miami, Fla., and in private practice there, discussed not only presently available hyaluronic acids, but also those that will become available in the future — describing the different products, their applications and the injection techniques he recommends.
Explaining how this natural and generally non-allergenic substance must be stabilized to achieve a longer half-life in human tissue, he says, "Unless they are cross-linked, hyaluronic acids will remain in the face for only a few hours."He says it is these cross-linking agents — not the hyaluronic acid itself — that cause allergic reactions that are generally so uncommon that allergy testing is considered unnecessary.
The potentially offending agents in the animal-derived form would be the animal proteins for this purpose, while in non-animal derived form, it would be the lab-fermented bacteria with which they are cross-linked.
Animal-derived hyaluronic acids Among hyaluronic acids that are animal-derived — in this case, from rooster combs — are Hylaform (Inamed) as well as its newly approved "more robust" version, Hylaform Plus.
Hylaform and Hylaform Plus can be used to contour the face, cheeks, chin, nasolabial folds, lips or lip lines. However, because of its larger particle size, Dr. Brandt explains, Hylaform Plus tends to last longer and should be used to achieve a fuller result, as with lips and deeper lines.
Non-animal derived hyaluronic acids
The Restylane (Q-Med) family are those products stabilized via bacterial fermentation in a lab. It includes four products, among which only the original Restylane is currently available in the U.S. The others are Restylane Touch, a reformulation of Restylane Fine Lines, which was considered to be overly viscous for the applications for which it was designed; Perlane, which is more viscous than Restylane; and Restylane Sub Q, which is the thickest of the Restylane formulations.
Particle size, concentration Explaining the relationship between particle size and concentration, Dr. Brandt says, "All of these products have the same concentration — 20 mg per mL of hyaluronic acid — but the more robust formulations, like SubQ and Perlane, have larger particle size, while Restylane and Restylane Touch have smaller particle sizes. However, despite having the same concentration, with increased particle size, the number of particles per mL decreases."
Injection techniques Although the size of the needle varies according to the thickness of the product, Dr. Brandt says the material can be injected using either a threading or linear puncture technique. Admitting that he, himself, prefers the retrograde serial threading method, he says, "It's not how you're doing it; it's where you're placing the material." He also cautions against over-correction when using hyaluronic acids.
Similar in viscosity, Hylaform and Restylane are injected through a 30-gauge needle into the mid-dermis, while Hylaform Plus and Perlane are injected slightly deeper into the dermis with a 27-gauge needle. The thinnest of the materials, Restylane Touch can be injected with a 30- or 32-gauge needle. The densest, SubQ, which is generally used for tissue contouring, is injected like fat, below the dermis through a 16- or 18-gauge blunt tip cannula.
These human-derived collagens were created as non-allergenic versions of their bovine counterparts (Zyderm and Zyplast, Inamed). Both contain 35 mg per mL of collagen; and the thicker Cosmoplast is crosslinked with glutaraldehyde, which is synthesized in the lab. Their advantage — no skin test is required.
Injection techniques Both human and bovine forms of collagen are injected through a 30-gauge needle.