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Choosing the right Hyaluronic Acid Filler
Researchers comparing the intradermal durability of three hyaluronic acid filler types—biphasic, monophasic mono-densified, and monophasic poly-densified—report that at six months post intradermal injection, biphasic and monophasic mono-densified fillers were more durable than the monophasic poly-densified filler.
Adilson da Costa, M.D., MS.c., Ph.D., lead author of the study published in the Aesthetic Surgery Journal, says this research offers physicians a comprehensive review of the differences among biphasic, monophasic mono-densified and monophasic poly-densified fillers, as well as insight into the manufacturing process of these three categories of HA fillers, which directly impacts the durability of the fillers in the skin.
Biphasic fillers have cross-linked particles of HA dispersed in a non-cross-linked HA vehicle; therefore, the HA is heterogeneous.
Monophasic fillers consist of a homogeneous mixture of high and low-molecular-weight HA, making their application easier.
Monophasic fillers may be further categorized as mono-densified, in which cross-linking occurs after homogeneous mixing, or poly-densified when cross-linking occurs separately before the mixture is produced.
Armed with the knowledge of which biphasic HA fillers have the best durability, physicians can better differentiate the best HA filler for their patients based on several factors, including cost-benefit aspects.
“Indeed, this is the first histological study to evaluate the durability in humans of one representative HA filler from each category for six months,” Dr. da Costa says.
Dr. Costa and colleagues studied 25 volunteers, who received injections of three different fillers in the dermis of the right lumbar region. One of the volunteers dropped out for personal reasons.
Researchers injected equal amounts of the fillers into three different sites—in the same column—yielding nine points of application in each patient. They biopsied each line on days 2, 92 and 184. The skin samples were analyzed histologically, and the presence or absence of these fillers was verified by a dermatopathologist.
During a period of 182 days post injections, the researchers found that the amount of biphasic decreased by 12.5%; the monophasic mono-densified decreased by 25% and the monophasic poly-densified filler decreased by 62.5%.
The reduction in the biphasic product’s histologic presence was not statistically significant over six months, when researchers compared days 92 versus 2, 182 versus 92, and 182 versus 2.
“Interestingly, the histological presence of the biphasic and monophasic mono-densified fillers was statistically similar throughout the trial.” “Furthermore, the amount of monophasic poly-densified filler was equal to that of the monophasic monodensified filler at three months after injection, but the amount of monophasic monodensified filler remaining after six months exceeded that of the monophasic poly-densified filler.”
In summary, the durability of the dermal biphasic HA-based filler was similar to that of the monophasic mono-densified filler – both of which were superior to the monophasic poly-densified filler.
The three filler types are classified as cross-linked fillers, meaning they have intermolecular bonds—mainly, divinyl sulfone, 1,4-butanediol di-glycidyl ether (BDDE), or p-phenylene bisethyl carbodiimide—which make stability and durability higher when injected into the dermis, he says.
“Physicians consider cross-linked HA fillers as ‘heavier’ injectables, and they are the most common fillers used worldwide.”