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Fundamentos del Rayo Laser en Medicina y Cirugia Dental
Si no puede leer ingles, le enviamos la traduccion al español de este articulo.Cliqueando en dentista@yanez-polo.com, se la hacemos llegar de inmediato.

F U N D A M E N T A L S OF LA S E R S

The word LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. A brief description of each of those five words will begin to explain the unique qualities of a laser instrument, and, in turn, will become the foundation for further elaboration of the uses of lasers in dentistry.

Light is a form of electromagnetic energy that travels in waves, at a constant velocity. The basic unit of this radiant energy is called a photon, or a “particle” of light. A wave of photons can be defined by two basic properties. The first is amplitude, which is defined the total height of the wave oscillation from the top of the peak to the bottom. This is a measurement of the amount of energy in the wave: the larger the amplitude, the greater the amount of energy that can do useful work. A joule is a unit of energy; a useful quantity for dentistry is a milijoule, which is one-one thousandth of a joule. The second property of a wave is wavelength, which is the distance between any two corresponding points on the wave. This is measurement of physical size, which is very important both in respect to how the laser light is delivered to the surgical site and to how it reacts with tissue. Wavelength is measured in meters; and smaller units of this measurement are either microns (10 to the minus 6 meters) or nanometers (10 to the minus 9 meters.) A property of waves that is related to wavelength is frequency, which is the measurement of the number of wave oscillations per second. Frequency is inversely proportional to wavelength: the shorter the wavelength, the higher the frequency and vice versa.

Ordinary light produced by a table lamp, as an example, is usually a warm white glow. The white color seen by the human eye is really a sum of the many colors of the visible spectrum-- red, yellow, green, blue, and violet. The light is usually diffuse, not

focused. Light produced by a laser has opposite properties. Laser light is one specific color; a property called monochromatic, and is very finely focused. The precision of the beam is due to two additional characteristics: collimation and coherency.

Collimation refers to the beam having specific spatial boundaries. These boundaries insure that there is a constant beam size and shape that is emitted from the laser cavity. An X-ray beam has the identical property.

Coherency is a property unique to lasers. The light waves produced by a laser are a specific form of electromagnetic energy. A laser produces light waves that are physically identical. They are all in phase with one another and have identical amplitude, that is, all the peaks and valleys are same size. Thus a laser produces a monochromatic (though sometimes invisible,) collimated and coherent beam of light energy that can do the work of accomplishing the treatment objective. Using a household light fixture as an example, a 100-watt lamp will produce a moderate amount of light for a room area, with very little heat. The light it produces is of multiple colors, amplitudes and wavelengths, and is not coherent or well focused. 2 watts of laser light, which is monochromatic, collimated and coherent, can be used for a precise excision of a fibroma, and providing adequate hemostasis on the surgical site, without disturbing the surrounding tissue.

The term stimulated emission of radiation is based in the quantum theory of physics, first postulated by the Danish physicist Neils Bohr. A quantum, the smallest unit of energy, is released after an atom that had absorbed energy releases it. This is called spontaneous emission (Fig 1).

Albert Einstein used that concept and further theorized that an addition quantum of energy may be absorbed by the already energized atom and that would result in a release of two quanta. This energy is emitted, or radiated, as identical photons, travelling as a coherent wave. These photons are then in turn able to energize more atoms, which further emit additional identical photons, resulting in an amplification of the light energy, thus producing a laser. Fig 1. - Spontaneous Emission Fig. 2 - Stimulated Emission

The light waves produced by the laser are a specific form of electromagnetic energy. The electromagnetic spectrum is the entire collection of wave energy ranging from gamma rays, whose wavelength are about 10 to the minus 12 meters, to radio waves, whose wavelength can be thousands of meters. All available dental laser devices have emission wavelengths of approximately 0.5 microns, or 500 nanometers to 10.6 microns or 10,600 nanometers. That places them in either the visible or the invisible portion non-ionizing portion of the electromagnetic spectrum, (Figs. 3 & 4). It is important to note that the dividing line between the ionizing, cellular DNA mutagenic, portion of the spectrum and the non-ionizing portion is on the junction of ultraviolet and visible violet light.

Thus all dental lasers emit either a visible light wavelength or an invisible infrared light wavelength in the portion of that non-ionizing spectrum called thermal radiation.

Dental lasers are named for the chemical elements, molecules or compounds that comprise the core, or active medium, that is stimulated. This active medium can be a container of gas, a solid crystal rod, or a solid state electronic device. There are two gas active medium lasers used in dentistry today, Argon and Carbon Dioxide. The remainder that are currently available are either solid state semiconductors made with metals such as Gallium, Aluminum and Arsenide, or solid rods of garnet crystal made generally from Yttrium and Aluminum that are doped with the elements of Chromium, Neodymium, Holmium or Erbium.

Laser Delivery Systems, Emission Modes

The coherent, collimated beam of laser light must be able to be delivered to the target tissue in a manner that is both ergonomic and precise. There are two delivery systems used in dental lasers. One is a flexible hollow waveguide or tube that has an interior mirror finish. The laser energy is reflected along this tube and exits through a handpiece at the surgical end with the beam striking the tissue in a non-contact fashion, without directly touching it.

The second delivery system is a glass fiber optic cable. This cable can be even more pliant than the waveguide, has a corresponding decrease in weight and resistance to movement, and is usually smaller in diameter, with sizes ranging from 200 to 600 microns. Although the glass fiber is encased in a resilient sheath, it can be somewhat fragile and cannot be bent into a sharp angle. The fiber fits snugly into a handpiece with either the bare end protruding or in some cases with an attached glass-like tip. This fiber system can be used in either contact or non-contact mode; however, the majority of the time it is used in contact fashion, directly touching the surgical site.

All conventional dental instrumentation, either hand or rotary, must physically touch the tissue being treated, giving the operator instant feedback. As mentioned, dental lasers can be used either in contact or out of contact. Clinically, a laser used in contact can provide easy access to otherwise difficult to reach areas of tissue. The fiber tip can easily be inserted into a periodontal pocket to remove small amounts of granulation tissue, for example. In non-contact, the beam is aimed at the target at some distance away from it. This modality is useful for following various tissue contours, but the loss of tactile sensation demands that the surgeon pays close attention to the tissue interaction with the laser energy. All the invisible dental lasers are equipped with a separate aiming beam, which can either be laser or conventional light. The aiming beam is delivered co-axially along the fiber or waveguide and shows the operator the exact spot where the laser energy will be focused.

In either modality, the beam is focused by lenses within the laser itself. With the hollow waveguide, there will be a precise spot at the focal point where the energy is the greatest, and that spot should be used for incisional and excisional surgery. For the optic fiber, the focal point is at or near the tip of the fiber, which again has the greatest energy. When the handpiece is moved away from the tissue and away from the focal point, the beam is defocused, and becomes more divergent. At a small divergent distance, the beam can cover a wider area, which would be useful in achieving hemostasis. At a greater distance away, the beam will loose its effectiveness because the energy will dissipate.

Lasers with shorter emission wavelengths, such as argon, diode, and Nd:YAG can be easily designed with very small, flexible glass fibers. A laser such as the Er:YAG

presents challenges to the fiber technology because the wavelength is very large and will not fit into the crystalline molecules of the conducting glass very easily. A special and costly fiber design, also incorporating water and air tubes, is necessary for the wavelength to be delivered in contact mode. The largest dental wavelength, Carbon Dioxide, is much too large for glass, and

has to be conducted in a hollow tube, as described above.

The laser device can emit the light energy in one of three basic modes. The first is continuous wave, meaning that the beam is emitted at one power level continuously as long as the device is activated, by pressing on the footswitch. The second is termed gated-pulse mode, meaning that there are periodic alternations of the laser energy being on and off, much like a blinking light. This mode is achieved by the opening and closing of a mechanical shutter in front of the beam path of a continuous wave emission. The duration of on and off times of this type of laser is normally as small as a few milliseconds. The third mode is termed free-running pulsed mode. This mode is unique in that very large peak energies of laser light will be emitted for an extremely short time span, usually in microseconds, followed by a relatively long time in which the laser is off. For example, a free running pulsed laser with a pulse duration of 100 microseconds with pulses delivered at ten per second would mean that the energy at the surgical site is only present for one-one thousandth of a second and absent for the remaining 99.9% of that second. The timing of this emission is computer controlled, not mechanically as in the gated pulse device. The average power that the tissue experiences will therefore be small.

The important principle of any laser emission mode is that the light energy strikes the tissue for a certain length of time, producing a thermal interaction. If the laser is in a pulsed mode, either gated or free-running, the targeted tissue has some time to cool before the next pulse of laser energy is emitted. In continuous wave mode, the operator must cease the laser emission manually so that thermal relaxation of the tissue may occur.

Very thin or fragile soft tissue, for example, should be treated in a pulsed mode, so that the amount and rate of tissue removal will be slower, but the chance of irreversible thermal damage to the target tissue and the adjacent non-target tissue will be minimal. Longer intervals between pulses can also help to avoid the transfer of heat to the surrounding tissue. In addition, a gentle air stream or an air current from the high volume suction, will greatly aid in keeping the area cooler. Conversely, thick dense fibrous tissue requires more energy for removal and continuous wave emission will provide a more rapid yet safe speed of excision. In either case, if there is too much thermal energy is used, healing can be delayed, and increased postoperative discomfort can occur.

Laser Energy and Tissue Temperature

The thermal effect of laser energy on tissue primarily revolves around the water content of tissue and the temperature rise of the tissue. As the following table shows, when the target tissue containing water is elevated to a temperature of 100 degrees C., vaporization of the water within the tissue occurs, a process called ablation. Since soft tissue is composed of a very high percentage of water, excision of soft tissue commences at this temperature. At temperatures below 100 degrees C and above approximately 60 degrees, proteins begin to denature without any vaporization of the underlying tissue. This phenomenon is useful in surgically removing diseased granulomatous tissue, because if the tissue temperature can be controlled, the biologically healthy portion would remain intact. Conversely, if the tissue temperature is raised to about 200 degrees, it is dehydrated and then burned, and carbon is the end product. Carbon, unfortunately, is a high absorber of all wavelengths, so that it can become a heat sink as the lasing continues. The heat conduction will then cause a great deal of collateral thermal trauma to a wide area.

Tissue Temperature (oC) Observed Effect

37-50 Hyperthermia

>60 Coagulation, Protein Denaturation

70-90 Welding

100-150 Vaporization

>200 Carbonization

Laser Effects on Tissue

The light energy from a laser can have four different interactions with the target tissue, and these interactions will depend on the optical properties of that tissue.

The first is reflection, which is simply the beam redirecting itself off of the surface, having no effect on the target tissue. The reflected light could maintain its collimation in a narrow beam, or become more diffuse. As stated previously, the laser beam will generally become more divergent as the distance from the handpiece increases.

However, the beam from some lasers can still have adequate energy at distances over 3 meters. In any event, this reflection can be dangerous because the energy would be directed to an unintentional target, such as the eyes; and this is a major safety concern for laser operation. The safety aspects of laser use will be discussed later.

The second is absorption of the laser energy by the intended target tissue. This effect is the usual desirable effect, and the amount of energy that is absorbed by the tissue

depends on the tissue characteristics, such as pigmentation and water content, and on the laser wavelength and emission mode. Certain wavelengths are preferentially absorbed by certain tissue components and by water, and the detailed discussion will follow in the individual laser wavelengths.

In general, the shorter wavelengths from about 500-1000 nanometers are readily absorbed in pigmented tissue. Argon has a high affinity for melanin and especially hemoglobin in soft tissue. Diode and Nd:YAG have a high affinity for melanin and less interaction with hemoglobin. The longer wavelengths are more interactive with water and hydroxyapatite. Ho:YAG has a good affinity for water; the largest absorption peak for water is just below 3000nm, which is at the Er:YAG wavelength. Erbium is also well absorbed by hydroxyapatite. Carbon Dioxide is well absorbed by both water and has the greatest affinity for tooth structure. The third effect is transmission of the laser energy directly through the tissue, with no effect on the target tissue. This effect is also highly dependent on the wavelength of laser light. Water, for example, is relatively transparent to the Nd:YAG wavelength, whereas tissue fluids readily absorb Carbon Dioxide at the outer surface, so there is very little energy transmitted to adjacent tissues. As another example, the diode and Nd:YAG lasers can be transmitted through the lens, iris, and cornea of the eye and can be absorbed on the retina.

The fourth effect is a scattering of the laser light, weakening the intended energy and possibly producing no useful biological effect. Scattering of the laser beam could cause heat transfer to the tissue adjacent to the surgical site, and unwanted damage could occur. However a beam deflected in different directions would be useful in facilitating the curing of composite resin.

The primary and beneficial effect of laser energy, therefore, is absorption of the laser light by the intended biological tissue. Dental laser surgery optimizes these photobiological effects. Incisions and excisions with accompanying precision and hemostasis are one of the many advantages of the laser device. There are photochemical effects that the laser can stimulate chemical reactions, such as the curing of composite resin, and break chemical bonds, such as the destruction of tumor cells using photosensitized drugs exposed to laser light. Certain biological pigments, when absorbing laser light can fluoresce, which can be used for caries detection within teeth. A laser can be used in a non-surgical mode for biostimulation of more rapid wound healing, pain relief, increased collagen growth and a general anti-inflammatory effect. The pulse of laser energy on hard dentinal tissues can produce a shock wave, which could then explode or pulverize the tissue, creating an abraded crater. This is an example of the photoacoustic effect of laser light. The principle effect of laser energy, as discussed above, is a photothermal one; that is the conversion of light energy into heat.

To summarize the tissue interaction effect of a particular machine, several factors must be considered. Each available laser has common internal parts but different delivery systems and emission modes. The laser wavelength will affect certain components of the target tissue; the water content, the color of the tissue, and the chemical composition are all inter-related. The diameter of the laser beam, whether delivered in contact or non-contact with the tissue, will create a certain energy density. The smaller the beam, the greater the energy density. For example a beam diameter of 200 microns compared with a beam diameter of 300 microns will have over twice as much energy density. The result of using the smaller fiber will be greatly increased thermal transfer from the laser to the tissue and a corresponding increase in absorption of heat in that smaller area. The amount of time that the beam is allowed to strike the target tissue will effect the rate of tissue temperature rise. That time can be regulated by the repetition rate of the pulsed laser emission mode as well. As mentioned earlier, the amount of cooling of the tissue by the use of a water or air spray will also affect the rate of vaporization.

Laser Safety

All laser devices have complete instructions on the safe use of the machine. There are certain fundamentals that all laser practitioners should know; however, the primary responsibility for the safe and effective operation of the laser is assigned to the laser safety officer. That person provides all the necessary information, inspects and maintains the laser and its accessories, and insures that all procedures for safety are carried out.

Appropriate protective eyewear for the patient and the entire surgical team must be worn when the laser is operating so that any reflected energy does no damage. The surgical environment has a warning sign and limited access. High volume suction must be used to evacuate the plume formed by tissue ablation. The laser itself must be in good working order so that the manufactured safeguards prevent accidental laser exposure.

Laser Regulatory Agencies

In various countries, there are a variety of regulatory agencies that control both the laser operator and the laser manufacturer, and these standards are strictly enforced.

In the United States, the American National Standards Institute provides guidance for the safe use of laser systems by specifically defining control measures for lasers. The Occupational Safety and Health Administration is primarily concerned with a safe workplace environment, and there are numerous requirements for laser protocol. The Center for Devices and Radiological Health (CDRH) is a bureau within the Food and Drug Administration (FDA) whose purpose is to standardize the manufacture of laser products and to enforce compliance with the Medical Devices Legislation. All laser manufacturers must obtain permission from the CDRH to make and distribute each device for a specific purpose; this is called marketing clearance, and means that the FDA is satisfied that the laser is both safe and effective to operate for that purpose. The owner’s manual then will instruct the operator on how to use the device for the particular indication for use that has been scrutinized by the CDRH. At the time of publication, in the United States, certain Argon, diode, Nd:YAG, Ho:YAG, Er,Cr:YSGG, Er:YAG, and Carbon Dioxide lasers have been granted marketing clearance by the FDA for intraoral soft tissue surgery. In addition, certain Argon lasers have clearance for curing of composite materials and tooth whitening, certain diode and Nd:YAG lasers for sulcular debridement (soft tissue curettage), certain Nd:YAG lasers for apthous ulcer treatment, certain Er,Cr:YSGG and Er:YAG lasers for caries removal, cavity preparation, and enamel roughening, and certain Carbon Dioxide lasers for tooth whitening. Clearance for other applications and other lasers may be pending.

The dental practitioner may use the laser for techniques other than the cleared indications for use, since the FDA does not regulate dental practice. Hospitals and institutions have their own credentialing programs for the use of lasers in their facilities, and a published curriculum guideline has established standards of dental laser education. The scope of practice as defined by the Dental Practice Act, the training, and clinical experience of the dental laser operator are the primary factors that should determine how the device is used.

Laser wavelengths used for dentistry

The following are brief descriptions of the available laser devices that have dental applications. The laser will be named according to its active medium, wavelength, delivery system, emission mode(s), tissue absorption, and clinical applications. Argon is laser with an active medium is Argon gas that is fiberoptically delivered in continuous wave and gated pulsed modes. This laser has two emission wavelengths, and both are visible to the human eye: 488nm, which is blue in color and 514 nm, which is blue green. The 488nm emission is exactly the wavelength needed to activate camphoroquinone, the most commonly used photoinitiator that causes polymerization of the resin in composite restorative materials. Using the argon light out of contact for this purpose results in a much shorter curing time compared to conventional dental lights, with the advantage of having an excessive amount of photons to ensure proper cure of the material. There are some studies that demonstrate some increase in the strength of the laser-cured resin when compared to resin that was cured with visible light. The Argon laser can also be used with other dental materials, such as light activated impression paste and light activated bleaching gels.

The 514nm wavelength has its peak absorption in red pigment. Thus, tissues containing hemoglobin, hemosidrin and melanin will readily interact with this laser; in fact, it is a very useful surgical laser with excellent hemostatic capabilities. Used in contact with the tissue, treatment of acute inflammatory periodontal disease and highly vascularized lesions, such as a hemangioma, would be ideally suited to the Argon laser.

Both wavelengths are not well absorbed in dental hard tissues and are very poorly absorbed in water. The poor absorption into enamel and dentin is advantageous when using this laser for cutting and sculpting gingival tissues, since there will be no interaction and thus no damage to the tooth surface during those procedures. Both wavelengths can also be used as an aid in caries detection. When the Argon laser light illuminates the tooth, the diseased, carious area appears a dark orange-red color, and is easily discernable from the surrounding healthy structures.

Diode has a solid active medium; in fact, it is a solid state semiconductor laser that uses some combination of Aluminum, Galium and Arsenide to change electrical energy into light energy. The available wavelengths for dental use range from about 800nm to 980 nm, placing them at the beginning of the near infrared invisible non-ionizing spectrum. Each machine delivers laser energy fiberoptically in continuous wave and gated pulsed modes, used ordinarily in contact with the tissue. The optic fiber needs to be cleaved and prepared before initial use and sometimes during the procedure to ensure the efficient operation of the laser. There are glass-like tips available that can be placed on the end of the fiber for certain applications. The wavelength range puts this laser into the invisible non-ionizing infrared radiation portion of the Electromagnetic Spectrum. All of the diode wavelengths are, like Argon, high absorbed by pigmented tissue, although hemostasis is not quite as rapid as with the Argon laser. These lasers are relatively poorly absorbed by tooth structure so that soft tissue surgery can be safely performed in close proximity to enamel dentin and cementum. The diode is an excellent soft tissue surgical laser, and indicated for cutting and coagulating gingiva and mucosa and for soft tissue curettage, or sulcular debridement. Care must be taken when using the continuous emission mode because of the rapid thermal increase in the target tissue. The chief advantage of the diode lasers is one of a smaller size instrument. The units are very portable and compact, easily moved with minimum setup time, and are the lowest price lasers currently available.

Nd:YAG has a solid active medium, a crystal of Yttrium Aluminum Garnet doped with Neodymium, and is fiberoptically delivered in a free running pulsed mode, used most often in contact with the tissue. It was the first laser designed exclusively for dentistry, and it is the laser with the largest market share. Additionally, it has extensive published scientific research for dental applications. The emission wavelength is 1064nm, in the near infrared invisible non-ionizing spectrum. It is highly absorbed by pigmented

tissue and is about ten thousand times more absorbed by water than an Argon laser. Utilizing the high peak powers of a free running pulse emission with relatively long tissue cooling time, common clinical applications are for cutting and coagulating of dental soft tissues with good hemostatic ability. The free running pulse mode also allows the clinician to treat very thin or fragile tissue with a reduction in heat buildup in the surrounding area. 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. There are numerous published clinical case studies showing effective periodontal disease control using this laser for sulcular debridement. There is also a useful clinical application in vaporizing pigmented surface carious lesions without removing the healthy surrounding enamel.

The fiber is usually used bare-ended, in contact with the tissue. During use, the fiber end needs to be cleaved and cleaned, otherwise the laser light will rapidly loose its effectiveness. When used in a non-contact, defocused mode, this wavelength can penetrate several millimeters into soft tissue, which can be used advantageously for delivering the laser energy to the inner surface of, for example, an ulcerated lesion.

Ho:YAG has a solid active medium, a crystal of Yttrium Aluminum Garnet doped with Holmium, and is fiberoptically delivered in contact with the tissue in free running pulsed mode. The wavelength produced by this laser is 2100nm, also in the near infrared invisible non-ionizing radiation spectrum. Its absorption by water is 100 times greater than Nd:YAG, and it has many soft tissue surgical uses. Since soft tissue contains a large amount of water, this laser can rapidly remove that tissue, and the optic fiber affords good access, precision and tactile feedback. Since this laser light has good absorption by water and is produced in a pulsed mode, the tissue ablation at the surgical site can proceed at an efficient rate and collateral thermal damage can be avoided. The pulse rate, or the amount of pulses of laser energy per second, is rather low compared to a Nd:YAG laser, and the resulting incisions can be somewhat jagged-edged. Clinically, this may only manifest itself on tissue that is more fibrous, but the healing result would still be very acceptable. The optical fiber, which is similar to the diode and Nd:YAG lasers, needs to be cleaned and cleaved periodically during surgery. A Holmium laser has little affinity for pigmented tissue; moreover, its hemostatic ability is decreased, again because of its lower absorbency into hemoglobin and other similar pigments. The laser’s absorbency by tooth structure is very low, which allows tissue surgery in close proximity to enamel, dentin or cementum to proceed safely. The Holmium laser is frequently used for arthroscopic surgery on the temporomandibular joint.

Erbium, Chromium:YSGG (2790nm) has an active medium of a solid crystal of Yttrium Scandium Gallium Garnet that is doped with both Erbium and Chromium. Erbium:YAG (2940nm) has an active medium of a solid crystal of Yttrium Aluminum Garnet that is doped with Erbium. Both of these wavelengths are near the boundary of the near and mid infrared, invisible, and non-ionizing portion of the spectrum. These two lasers will be discussed together because of their similar properties.

The world market offers Er:YAG machines that have the laser energy delivered in a hollow waveguide, through an articulated arm, or in a fiberoptic bundle. The Er,Cr:YSGG instrument delivers its energy fiberoptically. Both wavelengths are emitted in the free running pulsed mode. The technical challenge in building an optic fiber system stems from the fact that the wavelength’s size cannot easily be transmitted along the glass molecules, so the fiberoptic bundle is very costly, and can be fragile.

The fibers air-cooled and are a larger diameter than the other lasers mentioned, making this delivery system somewhat less flexible than the optic fibers of the Argon, diode, or Nd: and Ho:YAG machines. At the end of the fiber, a handpiece and a small diameter glass tip concentrate the laser energy down to a convenient surgical size, approximately 0.5 microns.

These two wavelengths have the highest absorption in water of any dental wavelength and also have a very high affinity for hydroxyapatite, although Erbium is approximately 20% higher than Erbium, Chromium in that regard. The laser energy couples into the hydroxy radical in the apatite crystal, and the water that is bound to the crystalline structures of the tooth will readily and easily absorb the laser light. The vaporization of the water within the mineral substrate causes a massive volume expansion, and this expansion causes the surrounding material to literally explode away. The free running pulse mode provides the peak power to facilitate the explosive expansion, and laboratory studies indicate that the pulpal temperature of the treated tooth may actually decrease by as much as 5 degrees C. during laser treatment.

These lasers are ideal for caries removal and tooth preparation when used with a water spray. Additionally, the sound tooth structure can be better preserved when the carious material is being ablated; the increased water content dental caries allows the laser to preferentially interact with that diseased tissue. The healthy enamel surface can be modified for increased adhesion of restorative material by exposing it to the laser energy. The current indication for use of these lasers dictates that they not be used for removal of amalgam, or other metal. However, the non-interaction with precious metal and fused porcelain allows the practitioner to remove caries surrounding these restorations without any damage. Both lasers can readily ablate soft tissue because of its high water content. In this modality, the water spray normally used in hard tissue interactions is turned off, and lower energy settings are used. The hemostatic ability is limited however, because only the water on the surface of the blood in the surgical site will be vaporized. There is no deep penetration to provide heat for rapid vessel shrinkage.

The advantage to these lasers for restorative dentistry is that a carious lesion in close proximity to the gingiva can be treated, and the soft tissue recontoured with the same instrumentation. Furthermore, tissue retraction for uncovering implants is very safe with these wavelengths, since there is minimal heat transferred during the procedure.

The Carbon Dioxide laser is a gas active medium laser that must be delivered through a hollow tube-like waveguide in either continuous or gated pulsed mode. The wavelength of 10600nm or 10.6 microns places it at the end of the mid infrared invisible non-ionizing portion of the spectrum. It is very well absorbed by water, second only to the Erbium series of lasers. It is a very rapid soft tissue remover; and has a very shallow depth of penetration in to tissue, which is important when treating mucosal lesions, for example. In addition, it is especially useful in cutting dense fibrous tissue. Moreover, it has the highest absorption in hydroxyapatite of any dental laser, about one thousand times greater than the Erbium series of lasers. Since this wavelength was one of the earliest used in general medical surgery, there are numerous published papers verifying its efficacy.

The Carbon Dioxide laser cannot be delivered in an optic fiber. Instead a hollow waveguide with a handpiece is used. The laser energy is conducted through the waveguide and is focused onto the surgical site in a non-contact fashion. The loss of tactile sensation is a disadvantage for the surgeon, but the tissue ablation can be very precise with careful technique. Large lesions can be easily treated using a simple back and forth motion; the procedure proceeds quickly since there is no need to touch the tissue. The current delivery system technology somewhat limits its hard tissue applications, but ongoing research shows very favorable results for surface modification and strengthening of tooth enamel for increased caries resistance. Summary The scientific basis and tissue effects of dental lasers have been discussed. It is most important for the dental practitioner to become very familiar with those principles and then choose the proper laser(s) for the intended clinical application. Although there is some overlap of the type of tissue interaction, each wavelength has specific qualities that will accomplish a specific treatment objective.

References Meserendio, Leo J, and Pick, Robert M. Lasers in Dentistry Chicago: Quintessence, 1995 Manni, JG, Dental Applications of Advanced Lasers. Burlington MA: JGM Associates, 1996. The Institute for Advanced Dental Technologies, Laser Dentistry, a Clinical Training Seminar. Southfield, MI, 1999. Atkins, PW, Physical Chemistry, ed.3. New York: WH Freeman, 1986. Catone GA, Alling, CC, Laser Applications in Oral and Maxillofacial Surgery. Philadelphia: WB Saunders, 1997. The Photonics Dictionary 43rd edition. Pittsfield, MA: Laurin Publishing, 1997. Mercer, C. Lasers in Dentistry: A review. Part 1. Dental Update, Vol.23(2), 1996. Coluzzi, DJ, et al, The Coming of Age of Lasers in Dentistry. Dentistry Today, October, 1998. Wigdor, HA, et al, Lasers in Dentistry. Lasers in Surgery and Medicine, Vol.16(2), 1995. Sliney, DH, Trokel, SL, Medical Lasers and Their Safe Use. New York: Springer-Verlag, 1993. American National Standards Institute, American National Standard for Safe Use of Lasers in Health Care Facilities. Orlando, FL: The Laser Institute of America, 1996. White, JM, et al, Curriculum Guidelines and Standards for Dental Laser Education, San Francisco, 1998. Kelsey III WP, et al, Application of the Argon Laser to Dentistry. Lasers in Surgery and Medicine, Vol. 11(6), 1991. Powell, GL, et al, Evaluation of Argon Laser and Conventional Light-Cured Composites. Journal of Clinical Laser Medicine and Surgery, Vol.13(5) 1995. Kutsch, VK Dental Caries Illumination with the Argon Laser. Journal of Clinical Laser Medicine and Surgery, Vol. 11(6), 1993. Finkbeiner, RL. The Results of 1328 Periodontal Pockets treated with the Argon Laser. Journal of Clinical Laser Medicine and Surgery Vol. 13(4), 1995. Moritz, A. et al, Bacterial Reduction in Periodontal Pockets Through Irradiation with A Diode Laser. Journal of Clinical Laser Medicine and Surgery, Vol.15(1) 1997. Myers, TD, et al, Conservative Soft Tissue Management with the Low-Powered Pulsed Nd:YAG Dental Laser. Practical Periodontics and Aesthetic Dentistry, Vol.4(6), 1992 White, JM, et al, Use of the Pulsed Nd:YAG Laser for intraoral Soft Tissue Surgery. Lasers in Surgery and Medicine, Vol. 11(5) 1991. White, JM, et al, Photothermal Laser Effects on Intraoral Soft Tissue in vitro. Journal of Restorative Dentistry, Vol. 70, 1992. Barr, RE, et al, Laser Sulcular Debridement: The Newest Weapon in Fighting Periodontitis. Dentistry Today, September 1998. Gutierrez, T, and Raffetto, N, Managing Soft Tissue Using a Laser: A 5-Year Retrospective. Dentistry Today, September 1999. Kautzky, M. et al, Soft-Tissue Effects of the Holmium:YAG Laser. Lasers in Surgery And Medicine Vol.20(3), 1997. Hendler, BH, et al, Holmium:YAG laser arthoscopy of the Temporomandibular Joint. Journal of Oral and Maxillofacial Surgery, Vol. 50 (9) 1992. Eversole, LR and Rizoiu, IM, Prelimiary Investigations on the Utility of an Erbium, Chromium YSGG Laser. Journal of the California Dental Association, Vol23 (12), 1995. Hossain, M, et al Effects of Er, Cr, YSGG Laser Irradiation in Human Enamel and Dentin. Journal of Clinical Laser Medicine and Surgery, Vol.17(4) 1999. Aoki, A. et al. A Comparison of Conventional Handpiece versus Erbium:YAG laser For Caries in vitro. Journal of Restorative Dentistry Vol.77(6) 1998. Dostalova, T, et al, Noncontact Er:YAG Laser Ablation: Clinical Evaluation. Journal of Clinical Laser Medicine and Surgery Vol. 16(5) 1998. Rechmann, P, et al, Er;YAG Lasers in Dentistry: an Overview. SPIE—The International Society for Optical Engineering Vol.3248, 1998. Pick, RM and Pecaro, BC, Use of the CO2 Laser in Soft Tissue Dental Surgery. Lasers in Surgery and Medicine, Vol. 7(2) 1987. Featherstone, JDB, et al, Effect of Pulse Duration and Repetition rate on CO2 Laser Inhibition of Caries Progression. SPIE—The International Society for Optical Engineering Vol. 2672, 1996. Biography

Donald J. Coluzzi is in general practice in Redwood City, CA. He is a 1970 graduate of the University of Southern California School of Dentistry and a Fellow of the American College of Dentists. He is on the Faculty of the University of California at San Francisco School of Dentistry, and is Past President of the Academy of Laser Dentistry.

 
 


         

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