Lasers utilizing wavelengths of 1,064, 1,320, 1,450, and 1,540 nm were the first nonablative resurfacing modalities. Utilizing technology to cool the surface to protect the epidermis, these lasers effectively heat the dermis selectively, to a limited degree, to stimulate new collagen formation and tightening. The nonablative lasers will be discussed primarily for skin rejuvenation, as other uses, such as for acne scarring and hair removal, are addressed in detail in other chapters. The 1,064-nm wavelength laser reviewed in this section is a long-pulse system, in contrast to the Q-switched units popular for tattoo removal.
The near-infrared lasers induce thermal injury in the dermis, potentially heating and damaging collagen to the point of denaturation. The rate of denaturation is exponentially related to temperature. Because of this relationship, small temperature changes impact denaturation dramatically. The accumulation of denatured material rises exponentially with temperature but proportionally with time, and thus both the amount of energy delivered and exposure duration are important. At critical temperatures, depending on the tissue type, rapid denaturation occurs. In the dermis, the extracellular collagen protein is the dominant material in coagulation (denaturing) because elastin is extremely thermally stable, even at the temperature of boiling water. The melting point for collagen is between 60 and 70 degrees Celsius, and above these temperatures, dermal scars can result. Thus temperature levels within the collagen are critical to causing mild injury, resulting in production of new collagen versus complete denaturation with resultant scarring.