BACKGROUND

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Public perception. In addition to the speculation in professional circles about the contribution of lasers to dentistry, dentists must respond to patient’s inquiries and perceptions about laser technology and its usefulness. A recent survey conducted by the American Dental Association indicates that 31 percent of adults consider it very important for a dental practice to have a laser, 30 percent consider it important and 21 percent consider it somewhat important.¹ Although this survey does not discriminate between laser types and applications, it does highlight the marketability of lasers in dentistry. For some dentists, such public perception, and the perceived marketability that such a tool could lend one’s practice, could create pressure to rush toward implementing laser technology.

Although nearly two-thirds of consumers surveyed¹ would like to see lasers available for use in their dentists’ offices, only about 3.5 percent of dentists surveyed by the ADA in 2000 used lasers in their practices.² This relatively small percentage may be due, in part, to the ability to achieve equivalent clinical results with less expensive traditional methods.

Philosophy of care. In dentistry, decisions about incorporating new technologies depend, in part, on one’s philosophy of care. One philosophy may hold that new technology should be incorporated on the basis of whether it can improve the likelihood of obtaining a predetermined and desirable clinical outcome. This philosophy is in contrast to first choosing a technology that is new to the marketplace, and then looking for a clinical use for it. The first approach suggests a philosophy based primarily on the needs of the patient; the second mind-set places priority on acquiring new technology. We believe that improving patient care should take priority over keeping up with the latest technology when decisions are being made about equipping one’s office.

In addition, dentists should feel free to abandon a tool or technology if a new one comes along that can better serve patients’ needs, but practical matters such as cost and the user’s learning curve can limit this freedom. Thus, after considering the time and money that must be invested to make a technology work in the practice, dentists should rely on the best available scientific evidence when making a decision to purchase and incorporate new technologies. Before making a commitment, they should consider what the reliable scientific literature indicates about the technology’s safety, efficacy and effectiveness.

Dentists should consider a number of factors when deciding whether to incorporate laser systems into their practices.

In particular, dentists should consider a number of factors when deciding whether to incorporate laser systems into their practices. First, they should realize that several types of lasers exist, with certain lasers approved for certain uses in dentistry and some lasers specific to soft- or hard-tissue applications. In addition, laser systems add significant cost to the delivery of care, requiring a sizeable investment in capital and the need to learn how to use the equipment. Dentists and patients also should realize that laser-induced tissue trauma to the surgical site can add several more days to the healing process, and can cause dramatically abnormal appearances for up to 10 to 14 days after surgery.^3–6

This article is an effort to communicate to the profession the uses for lasers in dentistry that enjoy the best scientific support, and to clarify where the weaknesses lie for other promoted uses. It is not intended to be a comprehensive literature review; rather, it is meant to arm the practitioner with good science that he or she can use when deciding whether to invest in lasers.

	GOVERNMENT REGULATION VERSUS SCIENTIFIC STANDARDS

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The number of regulatory agencies in our country and their influence on our lives are tremendous, which can cause some confusion regarding the meaning of some of their proclamations. For example, many lasers now sold in the United States have a 510(k) clearance for marketing through the U.S. Food and Drug Administration, or FDA, but how many dentists understand what this clearance signifies?

FDA clearance. This clearance enables companies to expedite the process of entry to the marketplace for products the FDA considers similar to devices already on the market. Often, this 510(k) clearance is misconstrued as FDA approval, which requires multiple-site testing to demonstrate safety and efficacy. To obtain 510(k) clearance, manufacturers must demonstrate only results equivalent to those of an existing, approved technology.⁷ From the scientific perspective, however, such an abbreviated process has significant limitations.

State dental boards. Other examples of regulatory influence on the practice of dentistry come from state dental boards. Although their decisions regarding which technological applications are allowed certainly affect practicing dentists, such regulatory activity does not preclude our professional duty to continue to scientifically scrutinize all new treatment modalities. In other words, decisions made by regulatory bodies in regard to the use of new technologies do not represent the final word on the subject. Not all therapies allowed by state dental boards truly represent the standard of care. The decision regarding whether a treatment modality represents the standard of care is left to good science and the profession itself. We hope and expect that board decisions will reflect the best of science and our collective professional judgment.

The standards of good science, in contrast to the specific and unique needs and responsibilities of the FDA, make a distinction that the FDA’s 510(k) clearance process does not. Good science distinguishes between stand-alone comparisons and comparisons that use adjunctive therapies. For example, if one claimed that a laser could plane roots as well as could curettes, the study design would compare use of the laser alone versus the curette alone for root planing. In this case, the laser would have to produce an "equivalent" result for this use of the technology to be scientifically justified (assuming safety concerns have been addressed).

By contrast, if a laser is recommended for an adjunctive procedure, such as subgingival curettage after scaling and root planing, the standard that must be met is one of "superiority." This means that after scaling and root planing, the laser must demonstrate added benefit over scaling and root planing alone. This standard also applies to other adjunctive therapies, such as local drug delivery or administration of subantimicrobial-dose doxycycline when used in conjunction with scaling and root planing.

	SAFETY, EFFICACY AND EFFECTIVENESS

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Safety. When evaluating any product such as lasers for use in patient treatment, one must be sure that it succeeds in three arenas: safety, efficacy and effectiveness. Safety requires that collateral damage be assessed histologically at several time points and be verified as being within acceptable limits.^8,9 This assessment involves looking at the final healed result in terms of the preoperative state, and weighs any permanent, unwanted damage along with the clinical benefit. The risk-benefit ratio must be small, with a significant potential benefit to the patient.

The wavelength of the light is the primary determinant of the degree to which the light is absorbed in the target material.

Efficacy. Efficacy is the degree to which the therapy provides a beneficial result for the patient under the controlled conditions seen in a clinical trial. Ethically, laser treatment must show efficacy and an acceptable risk-benefit ratio for it to be put forward for public use.

Effectiveness. Effectiveness is the degree to which the therapy provides clinical success in an uncontrolled, real-world environment, and represents the final verdict. It is not uncommon for products to pass the efficacy test and then fail in the subsequent test of effectiveness in the field. One should keep in mind that both efficacy and effectiveness are required for the greatest confidence to be warranted.

From an ethical standpoint, it is important to use the best available evidence when making clinical decisions. Sometimes the best evidence comes from meta-analyses or from the results of well-conducted clinical trials. Sometimes, however, no direct evidence is available to use. In such cases, inferences sometimes can be made on the basis of other credible data and biological principles. This is part of good clinical judgment and constitutes a significant aspect of what we do as clinicians.

The important principle here, however, is that we must do all we can to obtain the best and most credible information available. We also must be willing to modify our practices to conform to this new information as it becomes available. We recommend caution in cases in which direct evidence of safety, efficacy and effectiveness is not available.

	LASER-INDUCED INTERACTION BETWEEN LIGHT AND TISSUE

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Lasers produce light energy within a narrow frequency range. For most practical purposes, the light produced by lasers can be considered to be monochromatic. Typically, lasers are named according to the active element within them that goes through the stimulated quantum transitions, which create the light. The wavelength (or, inversely, the frequency) of the light that a laser produces is characteristic of the particular active element. For example, all neodymium:yttrium-aluminum-garnet, or Nd:YAG, lasers of similar design produce light with a wavelength of 1.064 micrometers. All carbon dioxide, or CO₂, lasers of similar design produce light with a wavelength of 10.6 µm. Design modifications can shift, within limits, the wavelength used by a laser tool.

Laser energy penetration. The wavelength of the light is the primary determinant of the degree to which the light is absorbed in the target material (in our case, oral tissue).¹⁰ Depending on the tissue, some lasers penetrate deeper than others. By contrast, other laser wavelengths are limited to a shallow penetration and have a surface effect on tissue. The deeper the laser energy penetrates, the more it is scattered and distributed throughout the tissue. The degree to which this occurs also is affected by the power of the laser and exposure duration, but wavelength is the primary factor.

The depth of penetration that is characteristic of a wavelength is a critical feature that can influence its utility for any particular application. For example, the CO₂ laser penetrates only about 0.03 to 0.1 millimeters into tissue. This provides just enough depth to seal blood vessels, lymph vessels and nerve endings measuring up to 0.5 mm in diameter. The clinical result of this penetration is good hemostasis and minimal postoperative morbidity. By comparison, the Nd:YAG laser penetrates 2 to 5 mm into tissue. While this deeper exposure may be desirable for hemostasis in more vascular tissue such as the liver or kidney, it has caused concern about the risk of collateral damage in oral sites where bone and other hard tissue are within the range of energy.

Continuous and pulsed waveform. Wavelength works in concert with a feature called "waveform" to influence the actual tissue effect. Laser energy can be delivered in two waveforms, continuous and pulsed, which can result in different tissue effects. Continuous-wave lasers can deliver large amounts of energy to the tissue in a steady, uninterrupted stream, usually at low-to-moderate intensities. Methods of interrupting, or gating, this continuous-wave beam also exist. This usually is done to deliver short, precisely timed, low-to-moderate–intensity exposures, either singly or in a train of exposures, with a cooling-off period in between. Pulsed lasers typically deliver smaller amounts of energy to the tissue in interrupted bursts, often at much higher intensities than those with continuous or gated lasers.

The optical properties of the tissue come into play only with laser wavelengths that have low absorption (or, conversely, high penetration) in tissue. Transmission and scattering of energy to deeper areas can take place only before absorption occurs. Thus, they seldom occur with lasers whose energies are highly (or quickly) absorbed on the surface.

Once the light from dental lasers is absorbed, it is converted to heat. The thermal effects of this heat depend, in large part, on tissue composition (that is, the amount of water and organic and inorganic components in the tissue) and the length of time the beam is focused on the target tissue. The duration of exposure results in temperature increases that may cause the tissue to change in structure and composition. These changes may range from denaturation to vaporization and carbonization, and even melting followed by recrystallization in the case of hard tissue.

In addition to the heat generated by a laser beam, dentists should be aware that heat can be generated from the laser unit itself. For example, contact-tip pulsed Nd:YAG lasers deliver heat to the tissue from two sources: surface heat from the hot fiber tip and internal heat from the absorption that occurs after penetration and scattering of the light energy that passes beyond the fiber tip. Dentists must take both sources into account when assessing the thermal risk to the patient.

	WAVELENGTHS USED IN DENTISTRY

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Several laser wavelengths are used in dentistry (Table^11–31). In this section, we briefly discuss these wavelengths and the uses that are backed by good science.

CO₂ lasers can be used for a number of soft-tissue applications,³² including the following:

– soft-tissue incision and ablation;

– gingival troughing;

– esthetic contouring of gingiva;

– treatment of oral ulcers;

– frenectomy and gingivectomy;

– de-epithelialization of gingival tissue during periodontal regenerative procedures.

The CO₂ laser offers a number of advantages for such applications. It provides excellent hemostasis, offering the dentist a clear operating field and allowing for instant visual feedback. In addition, the CO₂ laser removes tissue efficiently and quickly and causes negligible concern about subsurface tissue damage, as the effect is on the surface only.³³ Postoperative pain usually is minimal to none.³⁴

As with any piece of equipment, the CO₂ laser also has some disadvantages. For example, wound healing can be delayed for a few days.³³ In addition, there is a lack of tactile feedback, because only the laser light (not a fiber tip) impinges on the tissue. However, feedback to the clinician is visual and typically excellent, because of the dry field of operation.

Dentists should be aware that CO₂-treated tissue will have a black/brown appearance, which is caused by a carbon residue that will easily rinse off within the first few days after the procedure. The exposed area can go through color changes for 10 to 14 days, eventually resulting in natural and healthy-looking gums.

Nd:YAG. The Nd:YAG laser operates at a wavelength of 1.064 µm in a high-intensity pulsed waveform.

Like the CO₂ laser, the Nd:YAG laser can be used to perform a number of soft-tissue applications, including the following³²:

– gingival troughing;

– esthetic contouring of gingiva;

– treatment of oral ulcers;

– frenectomy and gingivectomy.

In addition, the Nd:YAG laser can be used to remove incipient enamel caries,³⁵ although not as efficiently as can the erbium:YAG, or Er:YAG, or erbium, chromium:yttrium-selenium-gallium-garnet, or Er,Cr:YSGG, lasers.

The Nd:YAG laser also offers good hemostasis during soft-tissue procedures, which facilitates a clear operating field. 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.³⁶

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, and is associated with a decrease in pulpal function (that is, sensitivity).^37,38 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. Finally, wound healing in soft tissue can be delayed for a few days or more when the Nd:YAG laser is used.³

Er:YAG. The Er:YAG laser operates at a wavelength of 2.94 µm and in a pulsed waveform. The FDA has cleared it for use on cementum and bone, and it has a variety of hard-tissue applications, including the following:

– caries removal¹¹;

– cavity preparation in both enamel and dentin¹²;

– preparation of root canals.^13,14

The Er:YAG laser has a number of advantages. It produces clean, sharp margins in enamel and dentin. In addition, pulpal safety is not a significant concern,³⁹ because the depth of energy penetration is negligible.^40,41 One study⁴² suggested that pulps may respond even better to preparations done with the Er:YAG laser than those done with the bur. When the Er:YAG laser is used for caries removal, the patient usually does not require local anesthesia.⁴³ The laser is antimicrobial when used within root canals⁴⁴ and on root surfaces,⁴⁵ and it removes endotoxins from root surfaces.⁴⁶ Finally, vibration from the Er:YAG laser is less severe than that from the conventional high-speed drill, and it is less likely to provoke discomfort or pain.⁴⁷ The laser has shown potential for removing calculus during root débridement, and compares favorably with traditional root planing.^48,49

Argon lasers do not necessarily produce a resin with physical properties superior to those of resins cured with traditional halogen curing lights.

On the downside, the Er:YAG laser does not selectively remove calculus on root surfaces; it removes calculus, cementum and dentin together.⁵⁰

Er,Cr:YSGG. The Er,Cr:YSGG operates at a wavelength of 2.78 µm, with an extinction length in water of 1.0 µm (a measure that translates into a depth of 90 percent absorption). The waveform for the Er,Cr:YSGG laser is pulsed.

The Er,Cr:YSGG laser has several hard-tissue applications:

– enamel etching^15–17;

– caries removal^18,19;

– cavity preparation^18–20;

– in vitro bone cutting with no burning, melting or alteration of the calcium:phosphorus ratio^21,22;

– root canal preparation.²³

The Er,Cr:YSGG laser has a number of advantages. Multiple uses for the Er,Cr:YSGG laser make the economics of providing laser therapy more feasible. The laser produces a rough surface in enamel and dentin without significant cracking. In dentin, no smear layer remains, which suggests good results with bonding.¹⁶ The Er,Cr:YSGG laser is safe for the pulp.^51,52 When using the Er,Cr:YSGG laser, the dentist often does not need to administer local anesthetic for caries removal and cavity preparation.

The disadvantages of the Er,Cr:YSGG laser involve the etching results. With this laser, enamel etching produces bonds with a wide range of strengths, which can be unreliable.⁵³ To minimize leakage in resins, clinicians may need to acid-etch enamel after preparing cavities with the Er,Cr:YSGG laser.¹⁵

Other points of interest regarding the Er,Cr:YSGG laser include the fact that melting enamel with this laser increases resistance to acid demineralization.⁵⁴ In addition, dentists should realize that changing the characteristics of the air/water spray influences the tissue effect and ablation rate.⁵⁵

Argon. The argon laser operates at a wavelength of 457 to 502 nanometers, using a pulsed or continuous waveform.

The argon laser can be used for a variety of applications, including resin curing^24–30 and tooth bleaching.³¹ In addition, this laser has a number of soft-tissue applications, including gingival troughing, esthetic contouring of gingiva, treatment of oral ulcers, frenectomy and gingivectomy.⁵⁶ The primary advantage of the argon laser is that the laser operates at a wavelength that is absorbed by hemoglobin, which provides excellent hemostasis.⁵⁷

Dentists 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.^58,59 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.⁶⁰

Holmium:yttrium-aluminum-garnet, or Ho:YAG. The Ho:YAG laser operates at a wavelength of 2.1 µm, and uses a pulsed waveform.

This laser is used for soft-tissue incision and ablation procedures, including the following:

– gingival troughing;

– esthetic contouring of gingiva;

– treatment of oral ulcers;

– frenectomy and gingivectomy.

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.⁶¹

Although the Ho:YAG laser is bactericidal,⁶² it should not be used to decontaminate implants because it damages the implant surface.⁶³

Gallium-arsenide (or diode). The diode laser operates at a wavelength of 904 nm, and uses a pulsed or continuous waveform.

The diode laser has proven to be successful with soft-tissue incision and ablation. This laser can be used for the following:

– gingival troughing;

– esthetic contouring of gingiva;

– treatment of oral ulcers;

– frenectomy and gingivectomy.

We should point out that the diode laser does not affect the inflammatory function of monocytes or endothelial cells, or the adhesion of endothelial cells.⁶⁴ In addition, it can kill some microbes in the presence of a photosensitizer,⁶⁵ as well as some fungi in the presence of some dye photosensitizers.⁶⁶ Finally, within certain low-energy ranges, the diode laser can stimulate the proliferation of fibroblasts.⁶⁷

Laser curettage appears to be neither scientifically nor ethically justified.

	LASER CURETTAGE

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Laser curettage, or laser sulcular débridement, deserves separate mention. Both the Nd:YAG and gallium-arsenide (or diode) lasers are promoted for curettage. A critical review of the best available evidence, however, strongly indicates that there is no added benefit to the patient when this procedure is performed after traditional mechanical scaling and root planing.⁶⁸ Furthermore, the American Academy of Periodontology recently issued a statement that curettage adds no benefit as an adjunctive procedure, regardless of how it is performed (that is, mechanically, chemically or with laser energy), and that the profession as a whole considers curettage to have no clinical value.⁶⁹

Proponents of laser curettage point to the ability of these lasers to kill microorganisms. Although the data indicate that this effect is possible albeit inconsistent, it has not been correlated with an improvement in periodontal attachment level.⁶⁸ The gold standard for the effectiveness of a periodontal therapy such as root planing is its effect on the attachment level. Other adjunctive therapies, such as local drug delivery or subantimicrobial-dose doxycycline, have been shown to improve the attachment level. Curettage, with or without a laser, has not.

With no demonstrable benefit and with a significant risk of collateral damage to the periodontium, laser curettage appears to be neither scientifically nor ethically justified.

	LASER BLEACHING

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In October 1998, the ADA Council on Scientific Affairs reviewed laser-assisted bleaching ⁷⁰ The council concluded that because of concerns regarding pulpal safety and a lack of controlled clinical studies, the CO₂ laser could not be recommended for tooth-whitening applications. The council indicated, however, that the argon laser might be an acceptable replacement for the conventional curing light if the manufacturer’s suggested procedures are followed carefully. According to an ADA survey,² about 3.3 percent of dentists who have lasers use them for activating bleaching solutions for tooth-whitening procedures. Today, almost five years after this survey was conducted, there appears to be no new data to warrant any change from this position.

	LASER CARIES DETECTION

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Laser fluorescence appears to compare favorably with standard methods of caries detection in occlusal fissures.^71–74 However, some have voiced concern that while laser fluorescence has demonstrated good sensitivity and excellent reproducibility, it is not able to quantify the extent of decay.⁷² Laser fluorescence also has performed well in the detection of residual caries.⁷⁵ While safety is not a concern with this low-power laser application, more data are required to aid in the clinical interpretation of the results and to develop a clinically useful sense of the limits of this technology.

	DISCUSSION

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With the exception of laser fluorescence for caries detection, little evidence exists to support the notion that lasers currently produce superior results to those for procedures that have been cleared by the FDA. Some features of laser use, however, are attractive with regard to patient appeal. For example, postoperative healing after soft-tissue surgery with the CO₂ laser typically involves much less morbidity than that after traditional scalpel surgery. It is interesting that some early evidence suggests that Er:YAG laser energy can produce superior attachment levels after root débridement compared with mechanical root planing.⁴⁸ Such novel techniques, while requiring further development and testing, hold exciting potential.

What is perhaps the most important recent development in laser dentistry is the advent of the Er,Cr:YSGG laser, which is used with a water spray. This laser is capable of multiple applications because its interaction with tissue is strongly influenced by variations in the air-to-water ratio of the spray. It can be used on soft tissue, enamel, dentin and bone, and its shallow interaction minimizes the risk of collateral damage. Also, the ability to be used for multiple applications improves the economic feasibility of this laser. Another significant benefit of this laser is that it does not necessitate the use of local anesthestic in many operative procedures.

However, traditional methods of performing the same procedures still are more economical on a per-patient basis. Recent innovations to improve patient appeal and the multiple-use capability while achieving equivalent results make a strong argument in favor of the Er,Cr:YSGG laser.

	CONCLUSION

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The development of novel techniques to produce results that are superior to those of traditional methods, or to produce results not possible at all by current methods, would improve the case for use of lasers in dentistry. However, until the laser is shown scientifically to bring about results that are superior to those achieved with conventional means for a significant number of applications, dentists who choose not to use lasers should not consider themselves to be lesser practitioners for doing so.