Biostimulation Posted on 29 Aug 00:00 , 0 comments
Although dental lasers such as the neodymium-doped yttrium-aluminum-garnet (Nd:YAG), carbon dioxide (CO2), and erbium family are considered “hard” or “surgical” lasers, they may be producing a degree of biostimulation in the areas peripheral to the focal spot, where the energy is reduced to stimulatory levels
Various zones of effect surrounding the focal spot when using a surgical laser (CO2, Nd:YAG, erbium, diode). At the focal spot, vaporization occurs. Concentric to that is a zone of coagulation, where the proteins in the tissue have absorbed energy and have coagulated, but have not been vaporized. Concentric to that is the zone of denaturation, where tissue proteins have absorbed a sufficient amount of energy to be heated to the point of denaturation, but have not absorbed enough energy to be coagulated. Concentric to that is the zone of photothermal effect, where the tissue has absorbed enough energy to be heated, but not otherwise affected. Concentric to that is the zone of photostimulation, where some low-level laser activity can be found.
Some of the positive effects observed with the hard lasers may be explained by biostimulation. Pourzarandian et al.reported stimulation of human gingival fibroblasts by low-level Er:YAG irradiation, as well as increased prostaglandin E2 (PGE2) production through induction of cyclooxygenase-2 (COX-2) messenger ribonucleic acid (mRNA) in human gingival fibroblasts. Additionally, Er:YAG lasers may be used at lowest output and scanned at a slight distance (out of focus) to produce biostimulation. The problem with using these hard lasers in this manner is that no microprocessor informs the practitioner how to control the dosage, and the fibers are not adapted for biostimulation.
Biostimulation is not limited to the traditional near-IR wavelength window; such effects are even reported when using defocused CO2 lasers. The CO2 laser has an extremely poor penetration through tissue because it is so well absorbed at the surface, and the biological effects reported on deeper tissues may first appear improbable. However, the coherent light is absorbed in peripheral microvessels, and the clinical effect observed shows that LLLT has primary effects at the target as well as systemic effects through blood and lymph circulation. Thus, with minimal calculation, the owner of a “hard” laser can have a “soft” laser for free. Least complicated is the surgical diode laser, with simpler calculations and wavelengths within the traditional range of biostimulation.