Medical surgeons in the 1960s began using a new device that complemented and, in some cases, replaced the scalpel. That instrument was a laser, and during the 1980s, a carbon dioxide model was a common component in the operating suite. In 1989, the first laser specifically designed for dental use became available. Today there are dozens of indications for use with various dental laser devices; and the clinical applications continue to increase, making the laser one of dentistry's most exciting advances with unique patient benefits.
A laser produces light that is distinguished from ordinary light by two properties: one, it is a single color, also known as monochromaticism; two, the light waves are all coherent, which means that each wave is identical in size and shape. This monochromatic, coherent wave of light energy emerges from the laser device as a uniquely efficient source of energy.
Lasers are generically named for the material contained within the center of the device, called an optical cavity. The core of the cavity is composed of chemical elements, molecules, or compounds, and is called the active medium, which can be a container of gas, a crystal, or a solid-state semiconductor. One currently available dental laser uses carbon dioxide as a gaseous active medium. The other devices are either solid rods of garnet crystal combined with other elements or solid-state semiconductor wafers made with multiple layers of metals. For simplicity the semiconductor lasers are called diodes, and the crystal lasers are designated with acronyms such as Nd:YAG, Er,Cr:YSGG, or Er:YAG. Of course, individual manufacturers create trademarked model names.
The active medium's stimulation generates a specific wavelength of non-ionizing radiation. A few lasers emit visible light (the caries detecting system, for example); but nearly all the surgical lasers produce invisible infrared beams.
Each wavelength has a somewhat unique effect on dental structures, due to the specific absorption of that laser energy in the tissue. Some lasers are absorbed by blood and tissue pigments, while others are absorbed by water as well as hard tissue, like enamel, dentin, and bone.
More specifically, the wavelengths can be categorized into three groups:
Lasers produce light energy that can be absorbed by a target tissue, and this absorption process produces a thermal reaction in that tissue. Depending on the instrument's parameters and the optical properties of the tissue, the temperature will rise and various effects will occur. In general, most non-sporulating bacteria, including anaerobes, are readily deactivated at temperatures of 50 degrees C and above. The inflammatory soft tissue present in periodontal disease can be removed at 60 degrees C; moreover, hemostasis can also be achieved within the same heat parameters. Soft tissue excisional or incisional surgery is accomplished at 100 degrees C, where vaporization of intra- and extracellular water causes ablation, or removal of biological tissue. Likewise, the aqueous component of tooth structure and bone also boils at this temperature; thus cavity preparation, calculus removal, and osseous contouring can proceed.
There are two basic emission modes for dental lasers: continuous wave and pulsed. Continuous wave means that energy is emitted constantly for as long as the laser is activated. Carbon dioxide and diode lasers operate in this manner. Mechanical and electrical controls can produce a gated or chopped pulsing of the continuous output, helping to minimize the latent heat produced by these types of lasers. Free-running pulse mode is produced by a flashlamp, where true pulses, on the order of a few ten-thousandths of a second, emanate from the instrument. Nd:YAG, Er:YAG, and Er,Cr:YSGG devices operate as free-running pulsed lasers.
Current dental lasers employ various means to deliver the laser energy to the tissue. Nd:YAG and diode lasers use flexible small-diameter glass fibers which are usually used in contact with the tissue. Erbium and carbon dioxide devices use semi-flexible hollow waveguides or rigid sectional articulated arms; a few erbium lasers have larger, more rigid fibers. Some diode and erbium lasers employ additional small quartz or sapphire tips which attach to the operating handpiece, and other systems simply are used out of contact with the tissue.