Chapter 36: Nonablative Dermal Remodeling

INTRODUCTION

Although promising in their potential, ablative approaches to rejuvenating photodamaged skin, including both CO₂ and Er:YAG laser technology, are sometimes accompanied by untoward side effects and complications. The most common of these is postoperative erythema, experienced by virtually all patients treated with ablative resurfacing. Other potential risks induced by these dermal wounding lasers consist of delayed healing, postoperative pigmentary changes, and scarring, which may be seen not only in patients with lower Fitzpatrick skin types, but also in patients with higher Fitzpatrick skin types. These risks, in addition to a prolonged recovery period after treatment, have prompted the development of nonablative and more recently, fractionated resurfacing technologies.

The clinical improvement noted after ablative laser therapy results from dermal wounding, which stimulates new collagen formation and deposition in a parallel configuration. Techniques that induce a dermal wound without epidermal ablation should, therefore, theoretically produce cosmetic improvement of dermal photodamage and scarring. This idea led to the development of newer rejuvenating laser systems known as nonablative dermal remodeling systems, which can be classified into three main groups: mid-infrared lasers, visible lasers, and intense pulsed light (IPL) sources. These groups operate on the principles of selective photothermolysis, as they target either a discrete chromophore or dermal water. Despite having different targets, these lasers, whether directed at dermal microvasculature, pigment or tissue water, produce similar histologic changes due to thermal injury. These changes in dermal collagen account for the clinical improvement observed after treatment with these modalities. The recent study and development of radiofrequency (RF) devices and fractional laser delivery systems has expanded the approach to using nonablative treatments for dermal remodeling. This chapter will review what is currently known about these treatment modalities.

INFRARED LASERS

The water absorption coefficient is relatively low in the infrared portion of the electromagnetic spectrum (>700 nm), which allows for deeper laser tissue penetration. Mid-infrared lasers typically used for photorejuvenation include the 1320 nm neodymium:yttrium–aluminum–garnet (Nd:YAG) laser, the 1450 nm diode laser, and the 1540 nm ytterbium–erbium:phosphate glass, also known as the erbium:glass (Er:glass) laser. Light produced by all three lasers is absorbed by water, with the 1320 nm wavelength absorbed least. As a result, optical penetration depth by this laser is the greatest of the three devices, with effective heating to the depth of 400 μm compared to a depth of approximately 300 μm achieved by the 1450 nm diode laser.¹ In addition, the 1320 nm wavelength is associated with significant scattering, resulting in deposition of energy outside the laser beam and subsequent effective dermal heating. Although low throughout the mid-infrared spectrum, laser light absorption by epidermal melanin is approximately 1.6 times lower at 1540 nm compared to 1320 nm.² It has, therefore, been suggested that the former wavelength may be safer to use in darkly pigmented individuals.

In one of the first studies evaluating a nonablative approach to dermal remodeling, ...