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Wavelength Laser YAG

Neodymium:YAG, Argon, and Holmium:YAG Lasers

Neodymium:YAG Laser

The Nd:YAG laser operates at a wavelength of 1064 nm and is fibre-optically delivered in a high-intensity free-running pulsed waveform which delivers the laser energy in extremely short bursts, allowing the tissue to relax thermally for a long period of time. This can be more comfortable to the patient. It is used most often in contact with the tissue. As with the diodes, the Nd:YAG fibre is usually used bare-ended, in contact with the tissue, but needs to be cleaved and cleaned, otherwise the laser light will rapidly lose its effectiveness. When used in a non-contact, defocused mode, this wavelength can penetrate several millimetres into soft tissue, which can be used advantageously for delivering the laser energy to the inner surface of, for example, an ulcerated lesion. Transmission of this laser wavelength, like diode, can be beneficial in having a bactericidal effect in accessory and lateral root canals.

The Nd:YAG wavelength is readily absorbed by pigmented tissues (melanin, haemoglobin), with some absorbance by water, which can be used to perform a number of soft-tissue applications, including the following1:

In addition, Nd:YAG laser energy is slightly absorbed by dental hard tissue, but there is little interaction with sound tooth structure, allowing tissue surgery adjacent to the tooth to be safe and precise. The Nd:YAG laser can be used to remove incipient enamel caries2, although not as efficiently as can the Er:YAG, or erbium, Er,Cr:YSGG, lasers.

The Nd:YAG laser also offers good haemostasis during soft-tissue procedures, which facilitates a clear operating field. The free-running pulse mode also allows the clinician to treat very thin tissue with a reduction in heat build-up in the surrounding area. In addition, the Nd:YAG laser offers a flexible fiber delivery system, avoiding the need for cumbersome articulated arm delivery systems.

The Nd:YAG laser has a number of disadvantages, however. It has the greatest depth of penetration of all the available dental surgical laser systems, which means that tissues under the surface are exposed to laser energy. This is cause for concern because of the risk of unwanted collateral damage, especially in the underlying bone or the dental pulp, as well as the associated postoperative morbidity.

In addition, the diminished localization of the energy on the tissue's surface makes vaporization of soft tissue with an Nd:YAG laser slower than with the better-absorbed laser wavelengths, such as those produced by the CO2 laser. Tissue vaporization can require a lag time until the activation point occurs (that is, the point at which the tissue begins to vaporize). To enhance the surface absorption of the energy (and shorten this lag time), some have recommended the topical application of photoabsorbing black dyes to the tissue.3

Direct exposure of the pulp by Nd:YAG laser light can occur when this wavelength of energy is directed at either the crown or the root of the tooth. Pulpal damage (such as denaturation and disruption of the vascular and neuronal tissue) from this laser can occur due to absorption of this energy by haemoglobin, and is associated with a decrease in pulpal function (i.e. sensitivity). 4, 5

Although decreasing sensitivity may be popular from the patient's perspective, it is important to realize that we do not know if this laser-induced pulpal damage will result in the need for endodontic therapy. One would expect that a compromised vasculature would decrease pulpal life expectancy. Therefore, the laser beam must not be directed straight at the tooth to avoid pulpal damage. Finally, wound healing in soft tissue can be delayed for a few days or more when the Nd:YAG laser is used.6

Argon Laser

The argon laser is fibre-optically delivered in continuous and gated pulsed waveforms, with two emission wavelengths (488nm and 514nm) both of which are visible to the human eye.

The 488nm (blue colour) emission is the wavelength needed to activate camphoroquinone, the most commonly used photo-initiator that causes polymerization of the resin in composite materials.7-13 The argon laser used in non-contact mode for this purpose results in a much shorter curing time compared to conventional dental lights, with the advantage of having more complete cure of the material. In addition to this, the argon laser is used to accelerate power bleaching by being absorbed by dyes within the blenching gel and causing a slight heating effect of gel which promotes the breakdown of more reactive oxygenating perhydroxyl free radicals.14 We should be aware that, when used for resin curing, argon lasers do not necessarily produce a resin with physical properties superior to those of resins cured with traditional halogen curing lights.15, 16 In addition, some resins contain multiple initiators that activate at different wavelengths. This suggests that the relatively narrow spectrum of a laser might not be the best approach to activate the initiators.17

The 514nm (blue green) wavelength has its peak absorption in red pigment. Therefore, tissue containing haemoglobin and melanin will readily interact with this laser. It is a very useful surgical laser with excellent haemostatic capabilities.18 Used in contact with the tissue, treatment of acute inflammatory periodontal disease and highly vascularized lesions, such as a haemangioma, would be ideally suited to the argon laser.19

Argon laser has a number of soft-tissue applications20, including the following:

Holmium:YAG

The Ho:YAG laser operates at a wavelength of 2120 nm, and is fibre-optically delivered in a pulsed waveform. The Ho:YAG laser has as its primary action absorption into water. Blanched tissues and cartilaginous or fibrotic sites respond readily.Ho:YAG laser has a number of soft-tissue applications20, including the following:

The advantages of the Ho:YAG laser center on its surface effect on tissue. The Ho:YAG laser is less penetrating than the Nd:YAG laser and, therefore, is faster than the Nd:YAG at cutting soft tissue.21

Although the Ho:YAG laser is bactericidal,22 it should not be used to decontaminate implants because it damages the implant surface.23

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