INTRODUCTION
The practice of soft tissue augmentation has a long and imaginative history. Modern soft tissue augmentation dates back to the 1890s when Neuber used autologous fat grafts to restore facial volume loss.1 Since then, numerous implantable substances and devices have been touted to improve soft tissue defects and deficiencies. Paraffin, silicone and bovine collagen are a few of the early, once popular, products that fell out of favor due to adverse events and potential toxicities. Today, a large assortment of injectable fillers is available both in the U.S. and worldwide. Hyaluronic acid derivatives, calcium hydroxylapatite, poly-L-lactic acid, and polymethyl methacrylate are the most commonly used products. The recent introduction of several new products correlates with the exponential growth the dermal filler market has experienced in recent years. More than 1.6 million dermal filler treatments were performed in 2011, making them the second most popular nonsurgical cosmetic procedure performed in the US after neuromodulators.2 For practitioners seeking to optimize outcomes with soft tissue fillers, it is important to first understand the proportions and ratios associated with beauty. The aesthetically ideal face follows the framework of Phi, also known as the Golden Ratio or the Divine Proportion – 1:1.618033988.This ratio is consistently reproduced throughout the universe, nature and art as a natural measure of balance and symmetry. Phi can be defined as the point on a line at which the ratio of the smaller part to the larger is the same as the ratio of the larger part to the whole (Figure 1). Phi is an irrational number intimately connected with the Fibonacci Sequence; a series of numbers in which the next number is found by adding together the two numbers before it (Figure 2). The Fibonacci Sequence is the closest rational approximation to Phi (Figure 3). These basic principles of nature and beauty were first recognized over two thousand years ago and still apply today. The ideal human face can be perfectly divided into thirds horizontally and fifths vertically. Horizontally, the upper third of the face can be visualized between imaginary lines across the frontal hairline and glabella, middle third between the glabella and subnasale, and lower third between the subnasale and menton (Figure 4). Vertically, the face is equally proportioned with imaginary lines running through the lateral pinnae, lateral canthi and medial canthi. These proportions along with specific structures of the face can be individually subdivided, further demonstrating the ubiquity of Phi. Beauty is often associated with youthfulness as a youthful face more frequently approaches the above ratios. The youthful face also represents a point in time when the bone and soft tissues occupy the ideal volume for the overlying skin envelope, leading to smoother skin and smoother transitions of cosmetic units. An aged face, by contrast, moves away from desirable proportions and demonstrates more topographical irregularities and harsher transitions between facial boundaries. Facial aging is a complex and dynamic alteration of balance and proportion characterized by a myriad of features involving the bone, ligaments, fat, and skin that ultimately lead to volume loss and redistribution. The lower face widens as the jowls form and shortens as bone is remodeled in the maxilla and mandible.3-7 The orbital diameter increases and the maxillary height decreases. Several studies have demon- strated how these bony changes manifest visibly on the face.3-7 As bone resorbs, it leads to a smaller platform for the overlying soft tissues and causes a “folding in” of these tissues known as the concertina effect. Elongation of the nasal tip and loss of a definitive jawline reflect the forward movement and resorption of the maxilla and mandible.3-7 In the midface, redistribution, accumulation, and atrophy of fat lead to volume loss.8 Areas such as the forehead and cheeks lose fat while the mouth and jaw accumulate fat. Lipoatrophy of specific deep fat compartments, which support
