Update on Hyaluronic Acid Fillers for Facial Rejuvenation

Facial rejuvenation has become increasingly popular, with nonsurgical and noninvasive procedures comprising a large part of aesthetic practice. According to the American Society for Aesthetic Plastic Surgery, Americans spent $12 billion on cosmetic procedures in 2014, with more than 10 million surgical and nonsurgical procedures performed. The top 5 nonsurgical procedures for both men and women combined were botulinum toxin, hyaluronic acid (HA), hair removal, chemical peel, and microdermabrasion.¹

The first dermal filler used was bovine collagen, which was approved by the US Food and Drug Administration (FDA) in 1981. Despite its efficacy in the correction of facial rhytides, bovine collagen required allergy testing prior to use and was discontinued in 2010. Dermal fillers have evolved over the years, and newer products that are superior to earlier fillers with regard to longevity, safety, and tolerability and that do not require allergy testing have become available; however, advances in the use of dermal fillers are not only related to the development of newer products but also to evolving injection techniques. Initially, the aim of treatment with dermal fillers was to correct lines and wrinkles, but an increased understanding of the complex changes that occur with aging have changed our approach to one of volume replacement, with an emphasis on volume restoration in the midface. This approach requires an in-depth understanding of facial anatomy as well as the interactions of the skin, soft tissue, muscle, and bone. Furthermore, placement of filler in specific fat compartments can provide a more natural appearance and an all-around youthful face.² In this article, we discuss HA fillers that have gained FDA approval within the last 5 years (Table).

Overview of HA Fillers

Hyaluronic acid is a naturally occurring linear glycosaminoglycan with a disaccharide unit, which repeats several thousand times.³ Hyaluronic acid is an essential part of the extracellular matrix of many tissues including the dermis and plays an important role in tissue growth, development, and wound healing. Hyaluronic acid is hygroscopic and absorbs water extensively, thus creating volume.⁴ Treatment with HA fillers is popular, as they are biocompatible and have a low potential for allergic reactions. They also are easy to use and reversible.⁴ The first HA filler to gain FDA approval was Restylane (Galderma Laboratories, LP). Currently, several HA fillers are approved in the United States, and each product differs from the others in polymer chain length, degree of HA concentration, particle size, gel consistency, gel hardness, gel viscosity, and degree of water solubility, as well as amount and degree of cross-linking. Cross-linking is essential to avoid enzymatic degradation by endogenous hyaluronidase when injected into the skin and thus to prolong the product’s half-life.⁵ Cross-linkers used to manufacture HA fillers include 1,4-butanediol diglycidyl ether and divinyl sulfone. More concentrated products with a greater degree of cross-linking provide increased longevity, but they are associated with a higher risk for inflammation and nodule formation. The elastic modulus (G′) is a measure of the firmness of dermal fillers, describing their resistance to deformation. Materials with a higher G′ are stiffer and are meant for deeper injections. Hyaluronic acid fillers can be further classified as biphasic or monophasic. Biphasic fillers (eg, Restylane, Perlane [Galderma Laboratories, LP]) contain a range of microsphere sizes, while monophasic fillers (eg, Juvéderm [Allergan, Inc], Belotero Balance [Merz North America, Inc]) contain homogeneous microspheres. Although randomized clinical trials have reported comparable efficacy and durability of biphasic and monophasic fillers when used to treat the nasolabial folds,^6-8 monophasic HA fillers are more cohesive and may not migrate as much following injection.

Restylane Family

Restylane was the first FDA-approved HA filler, gaining its approval in 2003. Restylane is a nonanimal stabilized HA (NASHA) that is produced from the fermentation of equine streptococci. It is cross-linked with 1,4-butanediol diglycidyl ether with a 1% degree of cross-linking. Restylane has an HA concentration of 20 mg/mL. The particle size range of Restylane and Restylane-L is 330 to 430 mm. Restylane (and also Perlane) get passed through sizing screens via sieves and are quantified by their size. The longevity of HA fillers is approximately 6 months; however, various factors affect the product’s longevity, such as the degree of cross-linking, treatment area, and the patient’s metabolism. Restylane-L, which was FDA approved in 2012, is a newer product with 0.3% lidocaine incorporated into the syringe itself. It was the first product from the Restylane range to be approved for lip augmentation. The addition of lidocaine (designated by the L in the product name) does not affect the longevity of a filler.⁹

The newest FDA-approved HA filler was Restylane Silk (approved in 2014), which has been specifically designed for lip augmentation and correction of perioral rhytides. To avoid postprocedural swelling, it generally is recommended that Restylane Silk be injected slowly. If required, a short course of oral prednisone may be administered after the procedure to treat any edema. Restylane Silk is less viscous than Restylane and requires less pressure to inject. Therefore, it is more suited for treatment of fine perioral lines, as it flows more easily. Because it contains 0.3% lidocaine, discomfort usually is minimal, with treatment lasting approximately 30 to 60 minutes. In the author’s experience (G.G.), Restylane Silk provides a softer correction, though one has to be careful to inject slowly to avoid postinjection swelling. Restylane Silk also may be suitable for neck rejuvenation (off label), but several treatment sessions usually are required. Patients should be warned that they are likely to experience ecchymoses. In our experience, the effects of Restylane Silk injections last approximately 6 to 9 months.