Invited Discussion on: Combining Calcium Hydroxylapatite and Hyaluronic Acid Fillers for Aesthetic Indications: Efficacy of an Innovative Hybrid Filler

Abstract

The constant growth of the minimal invasive aesthetic procedures sector during the pandemic, especially within the market of fillers for volume augmentation and skin regeneration has propelled both hyaluronic (HA) acid and calcium hydroxyapatite (CaHA) to the top of the ranking lists of non-surgical procedures with almost a million treatments in the US alone in 2021 [1]. The bad news is that as of today, there is still no onedoes-it-all product that can deliver effective volume augmentation and significant collagen/elastin stimulation at the same time; therefore, we commend the authors of this study [2] for the boldness and creativity of further developing and fostering an idea that was first described by Chang [3] in 2020. As we all know from medical history, the indications for the use of certain products and techniques evolve based on creative ideas, thorough clinical observation and out-ofthe-box-thinking that in many cases changed our aesthetic practices forever, such as the development of an aesthetic indication for botulinum toxin described by Carruthers et al. [4]. With facial ageing being a progressive, 3-dimensional process occurring in multiple layers, that would mean an ideal filler product could be used for many different indications: bone restoration, soft tissue volume restoration, collagen/elastin regeneration, dermal thickening and tightening and so on. As we all recognize that there is today no unique product on the market that in its original formulation can deliver these properties, there is an incessant quest to find combinations of products that achieve a more holistic result within one single procedure. The idea of mixing HA to obtain volume restoration with CaHA to enhance collagen stimulation is for sure very interesting and maybe promising, nevertheless, some limitations of the study must be highlighted. The effectiveness (high efficiency and efficacy) for volume restoration or soft tissue support of any given filler depends on its physical properties (rheology) as much as its capacity to induce neocollagenesis depends on its dilutiondiffusion ratio and the number of particles/area in contact with fibroblasts [5–7]. That means if cohesivity and rheology are changed, the g-lifting capacity of any HA filler may be reduced as much as a change in the diffusion and dilution characteristics of a CaHA filler may alter its capacity to induce collagen and elastin [6, 7]. To illustrate this interdependence we used high-frequency ultrasound (Logic E10, General Electrics, 24 Hz probe) during injection to visualize the lifting capacity (visible product height gain of each bolus) and depth diffusion (vertical product spread) of Belotero Volume (Merz Pharma , Germany) alone (Fig. 1), Radiesse (Merz Pharma , Germany) dilute 1:1 (1.5ml Radiesse ? 1.5 ml lidocaine 2% no epinephrine) alone (Fig. 2) and a premixture of both in a ratio 1:1 as mentioned in the study (Fig. 3). All injections were done using a 25 G cannula (Softfill 50mm) with 0.2 ml boluses/traces in a fresh donor skin sample. & Gabriela Casabona [email protected]