Depth of Penetration
Lasers’ and light-sources’ penetration through the skin is limited by many factors: energy density, skin type, scattering, pulse diameter et al, while radio-frequency devices depend greatly on the tissue hydration and impedance.
For JVR, the depth of penetration is directly related to pneumatic pressure generating delivery of liquid into the tissue. Published evidence shows penetration of the injected fluid down to 5 mm of depth and distributing it across the different skin layers.10,35 However, the latest generation of this technology allows even deeper penetration -- through the superficial skin, subcutaneous fat layer and fascia -- as being demonstrated by ultrasound (US) (Figure 3).
In comparison to JVR, ablative lasers and sublative radio frequency (RF) (Table 2) usually do not penetrate the deeper dermis. Non-ablative RFs can heat up skin and subcutaneous layers but their impact is limited.25 High-intensity focused ultrasound (HIFU) penetrates below the skin but its action is destructive, causing scarring rather than regeneration.27 Furthermore, once RF and HIFU are in proximity of the bony surfaces, the pain can be intolerable and limits the treatment efficacy.
Assessment of Thickening Effect
Several recent studies have shown that skin thicknesses, as well as the dermal density is important indicators of the regeneration process associated with the energy-based aesthetic technologies.
Histology Assessment
Quantitative assessment of skin thickening after JVR has been measured by histology, showing focal thickening of collagen fibers, increase in the number of dermal fibroblasts and focal upturn of elastin fibers.21
The ability to remodel skin and increase dermal thickness was proven for the following modalities - Er:YAG laser,13 pulsed dye laser,14 1320 nm Nd:YAG laser,37 intense pulse light (IPL),36 fractional RF needles,52 poly-L-lactic acid filler,30 and calcium hydroxyapatite. 32 Abdominal skin therapy with 1064 nm Nd:YAG laser demonstrated thickening and reorganization of collagen fibers within the laser-exposed lower reticulum and fibro-septal system.41 Use of 1440 nm Nd:YAG laser for the neck contouring resulted in average 31% increase in skin thickness 3 months after a single session. Histopathology examination following several TriPollar RF treatments in periorbital and perioral areas revealed 49% increase in dermal thickening. The increase appears to be due to focal thickening of collagen fibers.21,38 As for HIFU, histometric analysis of the skin samples two months after the treatment showed 23%-thickness increase of the dermis. 27 Dermal fillers, such as poly-L-lactic acid, HA, and calcium hydroxyapatite can increase collagen production.30-32 In these publications, the comparison was done between treated and untreated skin from non-specified sites. In our series, the skin from the same area was compared before and after treatment and results revealed positive effect on the dermal thickness.
Histological findings after multiple JVR treatments with hyaluronic acid showed an increased amount of collagen and increased dermal thickness.9 At four months after the treatment, regeneration of dermal structures, “notable augmentation of collagen type III and increased fibroblasts migration” were shown (Figure 4). Overall, there was a 175% increase of the dermis thickness in comparison to baseline.9 Clinically the authors reported a full Fitzpatrick–Goldman Wrinkle class reduction in face and neck and palpably thicker and visually more homogeneous skin in the chest and dorsal hands.
Ultrasound Assessment
The importance of ultrasound for dermal assessment is steadily increasing and gains recognition. Unlike histology, the measurements are made on live skin that was not undergone any modification or processing. Therefore, the findings represent
