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LASERS AND LIGHT AMPLIFICATION IN DENTISTRY

Dental lasers were introduced and recognized as a tool for better patient care in the early 1990s. In the ensuing years, clinicians have found that practicing cosmetic dentistry can be more exciting and rewarding by using laser technology for accomplishing general and cosmetic tasks. Clinicians in this specialized area seek to provide the highest caliber of care, while enhancing the esthetics of the smile. When considering a smile's components, cosmetic dentists focus on improvements related to the color, shape, alignment, and function of the teeth as well as the quality of the gingival architecture.

ARGON LASERS

The 488-nm wavelength of the argon laser has been used effectively to polymerize composite resins because it enhances the physical properties of the restorative material compared with conventional visible light curing.²⁴ Argon curing of dentin bonding also has improved adhesion compared with conventional visible light curing. Argon curing of sealants improves the attachment to the enamel surface and reduces microleakage significantly compared with conventional light curing.²⁹ The benefits of this procedure allow for enhanced physical properties, improved adhesion, and reduced microleakage, all accomplished in less curing time with argon lasers in 10-second cycles compared with a conventional curing light administered in 40-second cycles.^5-7 The 488-nm argon laser is an essential tool for a cosmetic or restorative dentist continually working with composite resins (the selection of the composites should be compatible with specific wavelengths). Another breakthrough accomplishment achieved by using the 488-nm blue light argon laser is tooth whitening, which is discussed in more detail subsequently.

The 514.5-nm green light argon is used to perform soft tissue procedures. Gingivoplasty, gingivectomy, crown lengthening, and troughing are among the services that can be carried out beautifully because of the intrinsic characteristic of the laser wavelength as it specifically targets hemoglobin. Coagulation and hemostasis are expected photothermal interactions that can be used to advantage with the 514.5-nm wavelength.

The argon lasers currently available on the market are the HGM dental 200, 300, and 400 series (HGM Medical Laser Systems, Salt Lake City, UT). These models are offered in 488-nm and 514.5-nm wavelengths. The following argon lasers are available only in 488-nm wavelengths for curing and tooth-whitening purposes: AccuCure 3000 (Lasermed, Salt Lake City, UT), Arago (Premier Laser Systems, Irvine, CA), and Cure Star (Lares, Chico, CA).

Nd:YAG LASERS

The Nd:YAG laser (yttrium-aluminum-garnet solid doped with neodymium) generates a wavelength at 1064 nm and is well absorbed by the pigmented tissues, hemoglobin, and hemosiderin, which are found in abundance in the gingival tissues. The pulsed Nd:YAG laser features an optic fiber delivery system which is ideal for soft tissue procedures, including gingivoplasty, soft tissue crown lengthening, gingivectomy, and frenectomy, with no intraoperative or postoperative discomfort; it also offers a clean working site with minimal bleeding. Postoperative sutures or dressings are unnecessary. The need for drug administration and prescriptions is decreased because of the analgesic effect of the Nd:YAG laser^3,27,30; the potential for infection is reduced because of the bactericidal effect of the pulsed Nd:YAG laser.^10,27,34

The pulsed Nd:YAG laser has been used to treat periodontal disease by eliminating the diseased pocket lining, harmful microbes, and enzymes.^3,27 The optic fibers are inserted into the periodontal pocket and transmit the appropriate amount of energy necessary to create the desired thermal effects. Healthy gingiva play an important role in the creation of a beautiful smile. The pulsed Nd:YAG is the most popular dental surgical laser, with a long research history. They are available through the following sources: PerioLase (Millennium Dental Technologies, Inc., Cerritos, CA) and PocketPro (Lares).

CO₂ LASERS

The carbon dioxide (CO₂) laser generates a mid-infrared wavelength at 10,600 nm, which is well absorbed by the water component of soft and hard tissues. The delivery systems use articulated arms or wave-guides, not optical fibers. The primary dental applications for the CO₂ laser are soft tissue procedures, such as gingivectomy, gingivoplasty, frenectomy, and biopsy. The thermal necrosis zone is shallow (usually 100 to 300 µm deep). The laser can vaporize soft tissue precisely and quickly in a noncontact mode and is especially good at cutting dense fibrous tissue or debulking substantial soft tissue masses. The available CO₂ lasers are the LX-20 (continuous-wave output, 20 W) and Nova-Pulse (superpulsing capability) by ESC Medical Systems (Bothell, WA).

DIODE LASERS

Diode lasers are semiconductor lasers used for all soft tissue procedures. The Aurora HL and Aurora SL (Premier Laser Systems) provide 1.5 to 6 W of 800 to 830 nm continuous-wave power for soft tissue surgeries and treating periodontal problems. The Ceralas D15 (Ceramoptec, Longmeadow, MA) is a 980-nm GaAlAs (Gallium-Aluminum-Arsenide) diode for soft tissue, periodontal, and bleach procedures. The Diolase ST 6.0 W (ADT, Corpus Christi, TX) and the LD-15 Soft Tissue (Biolase Technology Inc., San Clemente, CA) also are 800- to 830-nm lasers suitable for all soft tissue and periodontal procedures.

ERBIUM LASERS

The 2940-nm and 2780-nm wavelengths are well absorbed by water and hydroxyapatite. Both wavelengths are used for decontaminating cavity sites throughout preparation and removal of decay. There is no report of pain, vibration, or high-pitched noise experienced during the procedure. This is a true benefit from the patient's perspective. The low power settings featured in erbium laser usage are a boon when used in an etching technique in conjunction with a traditional acid-etch technique, resulting in increased surface bond strength.^13,19 Available erbium lasers are Centauri Er:YAG (Premier Laser Systems), 2940 nm for hard tissue and some soft tissue procedures; DELite (Continuum Biomedical, Dublin, CA), for hard tissue and some soft tissue procedures; and Millennium Hydrokinetic (Biolase Technology, Inc.), 2780 nm Er,Cr:YSGG (Erbium, Chromium, yttrium-scandium-gallium-garnet) laser for hard tissue and some soft tissue procedures.

LASER BLEACHING

The objective of laser bleaching is to achieve the ultimate power bleaching process using the most efficient energy source, while avoiding any adverse effects. Using the 488-nm argon laser as an energy source to excite the hydrogen peroxide molecule offers more advantages than other heating instruments. Argon lasers emit fairly short wavelengths (488 nm) with higher-energy photons; conversely, plasma-arc lamps, halogen lamps, and other heat lamps emit short wavelengths as well as longer invisible infrared thermal wavelengths (750 nm to 1 mm) with lower-energy photons and predictable high thermal character. This high thermal energy can create unfavorable pulpal responses.

The argon laser rapidly excites the already unstable and reactive hydrogen peroxide molecule; the energy then is absorbed into all intramolecular and intermolecular bonds and reaches eigenstate vibrations.⁴ The hydrogen peroxide molecule falls apart into different, extremely reactive ionic fragments that swiftly combine with the chromophilic structure of the organic molecules, altering them and producing simpler chemical chains. The result is a visually whitened tooth surface.

History of Bleaching

The desire to have whiter teeth and the bleaching technique have been documented since the mid-nineteenth century. Methods for bleaching nonvital teeth include combinations of chloride of lime, calcium hydrochloride, and acetic acid; oxalic acid, 25% ether peroxide, hydrogen dioxide and hydrogen peroxide, and pure chlorine have been used as bleaching agents for vital teeth. In the early twentieth century, the use of 35% hydrogen peroxide was recognized as the most effective bleaching agent. In 1950, Pearson administered heat and hydrogen peroxide for nonvital teeth bleaching.³¹ In 1976, Nutting and Poe²⁸ introduced the walking bleach technique, which uses 35% hydrogen peroxide and sodium perborate for nonvital teeth bleaching.

For vital teeth bleaching, in 1918, Abbot used high-intensity light, raising the temperature of the hydrogen peroxide rapidly to accelerate the chemical process of bleaching.³⁵ In the late 1960s, a successful technique for home bleaching was introduced by Klusmier, at which time he discovered that l0% carbamide peroxide loaded in a mouth guard with the intent to improve the gingival condition also resulted in a bleaching effect. By March 1989, Haywood and Heymann²² introduced and published this technique; in the 1990s, this procedure has been used widely by the dental community.

Some patients cannot complete the home bleaching process for various reasons, such as the high time investment required, discomfort or irritation from wearing the trays, or the unpleasant taste and gingival or stomach irritation from the bleaching gel. For such patients, power bleaching or in-office bleaching produces the whitening results quickly, without the long-term commitment of wearing trays; the patient visits the dentist once to have this procedure performed. It has grown more popular since bleaching became a basic dental cosmetic service.

The history of power bleaching goes back to Abbot's use of high-intensity light to raise the temperature of hydrogen peroxide, accelerating the chemical process of bleaching. Since the early 1980s, the heat lamp and heated spatula have been used as a heat source to accelerate the bleaching process of the concentrated hydrogen peroxide; this has been shown effective but also creates irritation to the pulp. The process of controlling the caustic 35% hydrogen peroxide liquid has been challenging.

The latest development of power bleaching has offered easy-to-use bleaching agents, essentially using highly concentrated hydrogen peroxide mixed with thickening agents or additional buffering agents, catalysts, or coloring agents. The energy source can be derived from blue-colored halogen curing lamps, infrared CO₂ lasers, and blue-colored plasma arc lamps as well as the cool blue argon laser and 980-nm GaAlAs lasers.

The goal of power bleaching is to whiten with efficiency, by obtaining controlled temperature elevation of the hydrogen peroxide on the tooth surface or by dumping high-energy photons to pump the hydrogen peroxide molecules up to the high vibrational eigenstate⁴ of the bleaching agents. The latter accelerates the chemical redox (reduction and oxidation processes occur simultaneously) actions of the bleaching process applied to the tooth surface but with no adverse pulpal effects.

Pulpal Responses

The heat element is favorable to accelerate the rate of reaction but unfavorable for maintaining pulpal health. Zach and Cohen³⁵ showed that intrapulpal temperature increases of 10°F, 20°F, and 30°F cause 15%, 60%, and 100% irreversible pulpal damage in monkeys. In another study, Cohen¹² attempted to measure incidental discomfort relative to vital bleaching procedures and to identify pulpal changes that would explain the sensitivity and pain phenomenon. He theorized that the heat builds up intrapulpal pressure, leading to the sensation of pain.

The in vitro study of Zwahten et al³⁷ proved that teeth treated with bleaching agents showed increased absorbance and less rising pulpal temperatures during laser or visible light curing exposure than teeth not treated with bleaching agents. In this study, 377-, 488-, 1064- and 2100-nm wavelengths were used, and various bleaching agents, such as Opalescence X (Ultradent Products, South Jordan, UT), Shofu Hi-Lite (Shofu Dental Corp., Menio Park, CA), and Quasar Brite (Interdent, Los Angeles, CA), were implemented. Combined use of the 488- nm wavelength with Shofu Hi-Lite elicited a raised minimum surface and pulp chamber temperature. The blue 488-nm wavelength coupled with a matching blue bleaching agent produced the minimally raised surface and pulp chamber temperature, establishing the ideal effect in patient pulpal comfort. Conversely, coupling the 488-nm blue light with a red bleaching material elicited a considerable increase in surface and pulpal temperature. The bleaching agent that absorbs the most energy should come in the complementary color to the wavelength used. Determining the most favorable protocol for power bleaching regarding exact energy settings, activation time span, exact concentration of the components, and color of the bleaching agents requires further research. Shin and White³² presented a study of tooth surface and pulpal temperature changes caused by visible light cure units, which concluded that high-intensity curing lights achieve surface temperatures that are greater than low-intensity curing lights in much less time. This higher surface temperature may achieve similar or superior bleaching in less time.

There is no apparent safety concern for pulpal temperature effects from the tested high-intensity curing light when exposure time is limited to 10 seconds or less per tooth. The present protocol works when high-intensity curing lights (plasma-arc lamp) are kept to 10-second exposure times to control the pulpal temperature. The ability of hydrogen peroxide to penetrate through enamel and dentin,^{9 21,25} as a result of the relatively low molecular weight of the peroxide molecule (30 g/mol),¹ may be accountable for the transient pulpal sensitivity occasionally experienced by some bleaching patients.

Bowles and Thompson⁸ have shown that some pulpal enzymes are sensitive to the combination of hydrogen peroxide and heat. Calculations made from their data, however, show that the quantity of hydrogen peroxide that produced inhibition was relatively large (in the range of 50 mg), whereas the present study reveals that only microgram quantities of hydrogen peroxide diffuse into the pulp. The quantitative difference explains why there is limited pulpal damage in clinical situations.⁹ More than 8 decades of conventional in-office vital teeth bleaching using a more concentrated (35%) hydrogen peroxide solution with heat or light has not resulted in pulpal necrosis except when the tooth was overheated or traumatized.^20,21

Bleaching Mechanism

All dental bleaching agents — the carbamide peroxide in concentrations of 10%, 15%, 16%, 20%, and 22% used in tray bleaching techniques or 35% to 50% hydrogen peroxide-based power bleaching agents — ionize and decompose to initiate the redox chemical reaction bleaching process. Do all bleaching agents decompose the same way? Do all bleaching processes have the same end constituents? The answers to both of these questions is probably no, and complex exploration is required when seeking answers to the mystery of ionization of hydrogen peroxide (HOOH).

The entire chemical bleaching process could produce different ions and proceed in different ways as follows:

1.    The ionization of HOOH produces the hydroxyl ions (OH^-) because of breakage of the weakest bond between the two oxygen atoms in the hydrogen peroxide molecule (see Eq. 3).¹⁴

2.    The ionization of HOOH produces the perhydroxyl ions (HOO^-), considered to be a stronger free radical,¹⁷ and hydrogen ion (H⁺) (see Eq. 4).

3.    The ionization of HOOH produces water (H₂O) molecules and oxygen ions (O^-2), a weaker free radical (see Eq. 5).

4.    The ionization of HOOH produces water and oxygen molecules in the presence of salivary peroxidase enzymes (see Eq. 2).¹¹

Free radical ions are unstable and immediately seek an available target with which to react. The larger, long-chained, darker colored molecule reacts easily with the free radicals, altering the optical structure of the molecule and creating a different optical structure. The stain on the tooth surface becomes invisible, or the larger, darker colored molecule becomes virtually dissociated into a smaller, shorter chained, and lighter colored molecule.

Equations

Equation of carbamide peroxide (urea peroxide) decomposing to hydrogen peroxide and urea:

CO(NH₂)₂·H₂O₂ -> H₂O₂ + CO(NH₂)₂           (Eq. 1)

Equation of hydrogen peroxide dissociated into water and oxygen molecules:

2H₂O₂ -> H₂O + O₂                   (Eq. 2) 

Equation of hydrogen peroxide decomposed to hydroxide ions:

HOOH -> HO• + •OH                   (Eq. 3)

Equation of hydrogen peroxide decomposed to perhydroxide ions and hydrogen ions:

HOOH -> HOO^- + H⁺                 (Eq. 4)

Equation of hydrogen peroxide decomposing to water molecule and oxygen ions:

HOOH -> HOH + O^-2                  (Eq. 5)

Rate of Reaction

The expeditious rate of reaction in laser bleaching makes one major beneficial difference when compared with other methods of bleaching. Because bleaching has a short history of research and study, a calculated, hard definition of how the chemical rate of reaction operates is in its infancy. Enough research has been concluded to assure clinicians that laser bleaching using the argon laser as an energy source with the highly concentrated HOOH is the most efficient method in the tooth-whitening process. These two components — the ideal energy source and high concentration of the bleaching gel — meet all the criteria required for achieving the ultimate rate of reaction. The bleaching process is a chemical reaction composed of different factors that determine the rate of the chemical reaction. The increase of the temperature, concentration of the reactants, and intensity of the light in a photochemical reaction are all proportional to the rate of the chemical reaction of the tooth whitening.^2,33

The pH value plays an important role in the rate of reaction in the bleaching process as well. Ionization of buffered hydrogen peroxide in the pH range of 9.5 to 10.8 produces more perhydroxyl HO^-2 free radicals. The result is a 50% greater bleaching effect in the same time allotment as other pH levels.^18,36 The average pH value found in various strengths of hydrogen peroxide is approximately 4. The acidity allows the hydrogen peroxide to have a longer shelf life; however, to achieve efficiency standards, it should be buffered to a much higher pH value with the salt of an alkaline base before being used as an agent for tooth whitening. A thickening agent is added for ease of control and handling.

Carbamide Peroxide Versus Hydrogen Peroxide as a Bleaching Agent

Carbamide peroxide is synonymous with urea peroxide, hydrogen peroxide carbamide, and perhydrol urea. Typically, these products contain carbopol (Carbopol 940, BF Goodrich Co., Charlotte, NC) or carboxypolymethylene polymer as thickening agents to improve the texture for ease of handling and better tissue adhesion in addition to their use as bleaching agents in tray bleaching methods. Carbamide peroxide is unstable and immediately dissociates into its constituent parts on contact with tissue, saliva, or moisture.

The usual tray bleaching method uses 10% to 15% strength carbamide peroxide decomposing to 3% to 5% hydrogen peroxide and 7% to 10% urea (see Eq. 1) once the solution comes into contact with moisture. Hydrogen peroxide is the active ingredient contained within the bleaching agent. It then continues decomposing into smaller constituent molecules or atoms. Urea continues to decompose into CO₂ and ammonia. Ammonia is a strong base, which then offers an elevated pH environment, one that is more favorable for bleaching and simultaneously controls the acidity associated with plaque retention.²¹ In the presence of salivary peroxidase enzymes, the hydrogen peroxide decomposes to the safer constituents of water and oxygen molecules as part of an inherent self-defense mechanism (see Eq. 2). Because of its unstable nature, hydrogen peroxide decomposes instantly to produce various free radical ions (see Eqs. 3-5). These ions react with the long-chained, dark-colored chromophile molecules, breaking into smaller, lighter colored structures. It also could be the phenomenon of altering the optical structure of the chromophile molecule, rendering the stain invisible.

The in-office power bleaching method most often uses 35% hydrogen peroxide, although some methods use 50% hydrogen peroxide, a strength 7 to 16 times higher than that used in at-home bleaching techniques. Some clinicians use 35% hydrogen peroxide solution without adding any salt of an alkaline base or buffering agent; instead, solution-saturated cotton or gauze is placed on the teeth. The isolation approach for this method of treatment includes a rubber dam that has been tightly ligated to the teeth with floss and, underneath the dam, a layer of protective material, such as Oraseal (Ultradent Products), applied to the gingival tissue. This bleaching method requires a close examination of the isolation technique to ensure that the caustic solution cannot leak through the rubber dam.

Other hydrogen peroxide agents used in the power bleaching method can be incorporated with silica powder to create a paste form for easy handling. This paste could eliminate the need for a rubber dam, requiring only the isolation and protection of the gingival tissue with paint or liquid dam or composite as a gingival barrier, and a weak base, such as sodium hydroxide, as a buffering agent to raise the pH value for more efficient bleaching. Various proprietary powders, sodium perborate (waterless hydrogen peroxide), or dyes could be formulated into the clinician's preferred bleaching agents. Experienced clinicians can determine the appropriate bleaching agent depending on their own working style and knowledge. Beginners should follow the protocol the manufacturer has recommended for their particular equipment.

Choosing a Laser for Bleaching

Three dental laser wavelengths have been cleared by the Food and Drug Administration (FDA) for tooth whitening: argon, CO₂, and the most recent 980- nm GaAlAs diode. In February 1996, Ion Laser Technology (ILT, Salt Lake City, UT) gained FDA clearance for ILT argon (approximately 480 nm) and ILT Genesis 2000 CO₂ laser (10,600 nm) with a patented bleaching gel and chemicals for laser tooth whitening. The laser method originally was patented by Yarborough, a dentist and inventor widely credited with introducing some of the presently used tooth-whitening methods to the dental community. Yarborough founded Brite Smile (Birmingham, AL) to commercialize laser tooth whitening; Brite Smile was then acquired by ILT. In 1998, ILT changed the process of laser manufacturing, and the company underwent reorganization. The Brite Smile Co (Walnut Creek, CA) changed its protocol in 1999 and currently uses the plasma- arc lamp as an energy source for teeth whitening in their Brite Smile Centers.

Yarborough's treatment concept for laser bleaching involves the mixture of 50% hydrogen peroxide in a sodium perborate, proprietary powder base. Argon laser energy is used first to remove deep-colored stains, followed by a CO₂ laser, which emits the mid-infrared thermal energy that is absorbed rapidly by water and the moist bleaching paste. The bleaching paste is applied several times; the teeth are then cleaned, followed by a final coating of fluoride gel. The CO₂ laser then is activated to promote the remineralization of the tooth surface. Caution should be exercised when using the CO₂ laser because the characteristic of this wavelength is thermal and well absorbed into water and hydroxyapatite, which are the primary components of enamel.

There is a need for research efforts in laser bleaching (defined by the author as a dentist-controlled, in-office procedure using a high concentration of hydrogen peroxide and an added energy source to accelerate the process of tooth whitening). The preferred energy source is argon laser energy. The visible blue light emits a high-energy photon that efficiently excites the hydrogen peroxide molecules to an eigenstate molecular vibration without any thermal effect. The thermal effect from the CO₂ is favorable for its rate of reaction, but the potentially adverse pulpal responses are a valid concern. The author does not have sufficient experience with the new 980-nm GaAlAs laser to comment on its efficacy in this procedure.

Should clinicians consider the plasma-arc lamp as an energy source for tooth whitening? To date, the research has focused on its application as a curing source for photoinitiating a camphoroquinone-tertiary amine-type composite system. Similar to the argon laser, the plasma-arc lamp can provide the high (>1000 mW/cm²) to medium (>500 mW/cm²) intensity of light needed to reduce curing time and ensure the full polymerization of the composite to gain its proper physical properties.¹⁵ Millar and Louca²⁶ noted that the Apollo plasma- arc lamp emits a high intensity (>1000 mW/cm²) for 3-second curing cycles; for bleaching cycles, at 820 mW/cm². Simultaneously the radiometer reading for infrared light shows the 3-second curing cycle to be approximately 50 mW/cm2, and the bleaching cycle is 21 mW/cm²—similar to and slightly higher than the halogen curing lamp. Measurement of the temperature rise at the fiberoptic tip on the 3-second curing cycle is approximately 20°C; one bleaching cycle is approximately 12°C, which is higher than the controlled halogen lamp at 6°C.²⁶ Duret¹⁶ emphasized that using the halogen lamps for 30 to 60 seconds potentially can raise the pulpal temperature from 4°C to 14°C, and when using the Apollo plasma-arc lamp for a 4-second bleaching cycle, the pulpal temperature can increase 2.2°C.^16,23 Before using plasma-arc lamps as an energy source for teeth whitening, clinicians must know the proper protocol and be aware of the existence of the infrared and thermal energy.

Safety Issues in Laser Bleaching

There are no compromises when it comes to safety; responsible clinicians must recognize the operational parameters of the energy source selected. The argon curing laser falls in the class III laser classification; this requires special training for operating the equipment and use of special eye protection with orange-colored lenses. The eyes are sensitive photoreceptors—everyone in the operatory area must wear these glasses. The intensity of the light used for bleaching must be blocked out with glasses with the proper optical density for specific wavelengths.

One must handle the caustic hydrogen peroxide with extreme caution. The patient should be acquainted fully with the procedure and well protected with a good isolation technique. There are different techniques for isolating the bleaching site, such as the well-ligated traditional rubber dam, painting a gingival barrier, or merely working with lip and cheek retractors. Whatever method the clinician feels the most confident with (this includes familiarity with each step of the procedure) is acceptable.

A first-aid kit should contain antioxidants such as vitamin E in liquid or capsule form and aloe vera gel. Even with all isolation techniques in place, a single spilled droplet of hydrogen peroxide or bleaching compound, within seconds, blanches and burns gingival tissue. The patient may express discomfort with body language because the isolation techniques in place may make verbal communication impossible. The clinician should remain calm and apply the vitamin E oil quickly; the symptoms subside within 1 minute.

The clinician must follow the protocol regarding the length of exposure time for the selected energy source, which depends on the intensity of the light (mW/cm²) and the particular wavelength. The shorter the wavelength, the higher the energy of the photon. Conversely, longer wavelengths carry lower energy with more of the thermal effect of the photon. The general rule for avoiding unfavorable pulpal responses is 30 seconds per tooth using the argon laser and 10 seconds per tooth for the plasma-arc lamp because its thermal energy is at a higher energy output. Usually, there is a recommended time period for chemical oxidation followed by the light oxidation (5 minutes for argon laser and 10 minutes for plasma-arc lamp). Some bleaching compounds (Power gel [Welch Allyn Dental Products, Skaneateles Falls, NY], Apollo Secret gel [DMD, Westlake, CA], and Hi-Lite [Shofu, Menio Park, CA]) give color indication when the redox process has been completed. Toxicologic considerations, such as cytotoxicity or acute systemic toxicity, are much less of a problem with in-office power bleaching than with the at-home tray bleaching because there is no chance for the patient to consume any bleaching gel or have long-term contact or exposure. Health care providers always want to keep the patient's well-being foremost before initiating any procedure. See the accompanying box for the author's protocol for laser bleaching.

	General Protocol for Laser Bleaching
	Clinical Cases and Summary