INTRODUCTION
As the years go by, the outer shell of the human body
changes its appearance. These skin alterations are often
narrowly focused on facial wrinkles, one of the most
visible signs of the aging process. Therefore, the majority of
approaches intending to reverse skin-aging signs are focused
on the treatment of wrinkles.1 However, it recently became evident,
that simply treating wrinkles is insufficient to restore a
youthful facial appearance. Moreover, the loss of facial volume
beneath the skin is considered to be the major contributor to
the appearance of advanced age.2,3
In a youthful face, deep and superficial fat is balanced, creating
a round and even distribution of facial fullness.4-6 However,
as skin ages abrupt contour changes occur including sagging,
prominent nasolabial folds, hollow cheeks or deep circles under
the eyes.4,7 For many years, these skin aging signs were believed
to be caused by gravity,8,9 but recent research elucidated that
subcutaneous adipose fat of the face is partitioned into multiple,
discrete compartments, or fat pads, rather than being one confluent
mass.6 With aging, atrophy of adipose tissues of the face, due
to a progressive breakdown of subcutaneous cell components
occurs, resulting in inferior volume shift inside each compartment
as well as migration of some compartments independently
of each other, appearing then as separate entities.4,10 The reorganization
of the fat pads with aging, together with craniofacial
remodeling consequently led to predictable facial volume loss
resulting in dramatic changes to the overall contour of the face.
Various surgical options to treat facial volume loss are available
including cheek implants or face-lift in combination with volume
redistribution.11 Although effective, surgery always implies
the inherent risk of anesthesia and requires substantial time for
recovery. Additional procedures, in which volume is augmented
is the use of autologous fat. However, this technique requires
a previous invasive procedure (eg, liposuction) to harvest subcutaneous
adipocytes, which adds to the risks of this type of
treatment.12,13 Due to recent advances in aesthetic dermatology,
volume restoration can also be accomplished with minimal risk
by using injectable dermal fillers.
The purpose of this article is to review the injectable dermal fillers
for volume augmentation and restoration approved by the
US Food and Drug Administration (FDA), namely poly-L-lactic
acid (PLLA), calcium hydroxylapatite (CaHA), and low-molecular-
weight (LMW) 20mg/ml hyaluronic acid (HA).
Injectable Volume Fillers
The first dermal injections for tissue augmentation were described
in the late 19th century, when Franz Neuber used
autologous fat as filler material to correct depressed facial defects.
Shortly thereafter, in 1899, the physician Robert Gersuny
introduced paraffin for tissue augmentation, which eventually
became a very common filler material for several years, until
the high incidence of severe side effect became evident.14
Towards the end of the last century numerous injectable dermal
fillers were developed, such as collagen and hyaluronic
acid.15 Although the introduction of these dermal fillers was a
turning point for the treatment of facial wrinkles, the realization
that using injectable filler implants in the deep dermal and
