Comment

Laser Curettage: Where Do We Stand?

Douglas N. Dederich, BSEE, DDS, MSc, PhD, and Gerald I. Drury, MS, DDS

Copyright 2002 Journal of the California Dental Association.

Authors

Douglas N. Dederich, BSEE, DDS, MSc, PhD, is the head of the Department of Periodontics at Louisiana State University School of Dentistry.

Gerald I. Drury, MS, DDS, is a board-certified clinical professor of advanced periodontics at the University of Southern California and practices in Hermosa Beach, Calif. He is editor of the Journal of the Western Society of Periodontology and president of the California Society of Periodontists.

The literature suggests that curettage has no benefit beyond traditional scaling and root planing. However, claims abound as to the benefits of curettage with the laser, including less postoperative pain, less bleeding, and reduction in microbial count. This paper explores whether any of these claims are true and whether laser curettage has any benefit in periodontal treatment.

Gingival curettage has been around a long time. Hirschfeld¹ listed four objectives of subgingival curettage:

* Remove all calculus;

* Remove granulation tissue;

* Cause hemorrhage to reduce edema; and

* Remove epithelial lining of the pocket.

When achieved, these goals appeared to have a predictably beneficial effect on the periodontal condition of most periodontal patients. Ramfjord and colleagues² documented the superior efficacy of this treatment regimen over no treatment at all. However, questions remained as to whether scaling and root planing or curettage, or even perhaps an interaction between the two, was mostly responsible for the observed improvement. Chace³ found that scaling and root planing was indispensable in this process and that it was questionable whether additional curettage was needed. Ainsle and Caffesse⁴ biometrically evaluated the results of scaling and root planing alone as opposed to scaling and root planing followed by gingival curettage. They found no difference in pocket depth reduction, no increase in attachment level, and no decrease in inflammation with the curettage. This, of course, suggested that gingival curettage is not necessary. Echevarra and Cafesse⁵ found that, in suprabony pockets, performing gingival curettage one month after scaling and root planing offered no additional benefit, again suggesting that curettage is not necessary. Lindhe and Nyman⁶ found that "granulation tissue removal in conjunction with flap surgery is not a critical measure for the establishment of conditions which are conducive for proper healing of the periodontal tissues."

Thus far, the only objective of Hirschfelds’ original four that apparently remains supported by the literature is the first: removal of all calculus. In 1989, the Proceedings of the World Workshop in Clinical Periodontics⁷ defined root planing as "a definitive treatment procedure designed to remove cementum or surface dentin that is rough, impregnated with calculus, or contaminated with toxins or microorganisms. ... When done in a thorough fashion, some unavoidable soft tissue removal occurs."

It thus seems that whatever soft tissue removal may be necessary may well occur during scaling and root planing and not require a separate effort through intentional curettage.

So, if additional curettage is not required after scaling and root planing, what is the justification for doing it with the laser? Claims of potential benefit abound. For example, claims of less postoperative pain^8,11 and less bleeding⁸ are common, and also claims of reduction in microbial count.^9-18 Interestingly, however, a distinction has been made between lowering the live bacterial count and removing bacterial accumulations from within the pocket.¹⁹ Could one be more important than the other? If so, how does scaling and root planing compare to laser therapy in achieving it? Does the reduction of the numbers of live subgingival microorganisms result in a clinical improvement? Is this alleged reduction of the numbers of live microorganisms by the laser sufficient rationale to justify its use? Just what are the benefits of intrapocket laser therapy? And, of course, what are the disadvantages? This paper is intended to give answers to these and other related questions.

Pulsed Infrared Energy in Tissue

The interaction of pulsed infrared laser light at 1.064 ìm wavelength is central to the understanding of all that follows. It is also where there is disagreement between some proponents of Nd:YAG (neodymium: yttrium aluminum garnet) laser curettage and those who still find themselves in opposition to this particular wavelength in this application. The critics’ concerns are about the risk of significant collateral damage and lack of demonstration of effectiveness in improving the periodontal condition, notwithstanding the FDA’s acceptance of "equivalency" with standard scaling and root planing. White and colleagues²⁰ have explained their position on this interaction:

"Tissue specificity and absorption of a specific emission wavelength applies only when there are linear optics with low energies such as spectroscopy ...

"The body is relatively opaque to laser light and penetration (transmission) of photons into tissue does not necessitate deep damage, any more than holding your hand in front of a bright light. Clinical laser use is a photothermal event occurring at the surface from the absorbed laser light ...

"Contact delivered pulsed Nd:YAG lasers do not cause the deep thermal penetrations as seen with non-contact continuous wave systems."

One might paraphrase this by saying that pulsing of the energy in current dental Nd:YAG laser systems provides intense enough energies at the fiber tip to negate the normal optical (i.e., transmissive) properties of the tissue and generate heat only at the surface where the tip is touching the tissue. While this wavelength of light penetrates to a significant depth in the tissue when in lower-intensity modes, such as continuous-wave, and carries along with it the risk of collateral damage in those areas, pulsing the energy prevents the penetration. Since the body is "opaque"²⁰ to pulsed energy, there is no need to worry about penetration, bone death, pulpal denaturation, etc. during laser curettage. While this position explains in large part the tendency of much of their work to ignore the effect of transmitted light (not heat, but light), it is nevertheless contradicted by much of the current clinical evidence. Furthermore, this position is scientifically untenable. For while at exceedingly high fluences, dielectric breakdown and nonlinear response (e.g., plasma formation) can occur, this is typically more common with Q-switched lasers than those currently used in dentistry. Next, the analogy of holding one’s hand in front of a bright (albeit low-intensity) polychromatic light to explain monochromatic, high-intensity, pulsed laser exposure is open to criticism to say the least, and certainly does not qualify as a scientifically justified explanation. Research into this phenomenon has suggested otherwise, calling into question the validity of this position.²¹ Furthermore, their characterization of clinical laser use as "a photothermal event occurring at the surface from the absorbed laser light" is only a partial truth. But so often, the partial truth can lead one down errant pathways as easily as an outright mistake. Tissue effect arises from both the deposition of energy to increase thermal vibrations (temperature) but also, at various points, the deposition of the latent heats of phase transformation, which, when satisfied, change phases in the components of the material in an essentially nonthermal fashion, i.e., these phase changes are typically associated with no concomitant increase in temperature in homogeneous materials and will occur over a relatively small temperature range in heterogeneous materials. In addition to this, one must understand that heat is created in two ways with a contact-tip Nd:YAG laser: 1) the tip itself heats up, and 2) transmitted energy is eventually absorbed at depth, after some scattering, and heat is generated at the point of absorption. Initially, 100 percent of the energy flows through a new tip; but, as time passes, the imperfections and nonzero absorption coefficient of the tip as well as cellular debris on the tip continue to absorb heat and increase in temperature. This temperature increase causes further imperfections in the lattice structure of the tip, resulting in even more temperature increase. The increase in absorption by the tip and debris, however, has limits. So, while the amount of energy transmitted through and beyond the tip does, in fact, decrease with exposure time, it levels out at a positive value and never goes to zero.²¹ What does this mean? There is always residual light energy directly transmitting into the tissue. And, of course, the response of the tissue to this is cumulative in nature. With Nd:YAG laser techniques often lasting 60, 120, 180 seconds or longer, the risk of damage is real and should be histologically determined prior to recommending intrapocket Nd:YAG laser therapy. And, of course, none of the above has addressed the lack of clinical evidence of any added benefit to using a laser.

Clinical Effects

Perhaps the one thing that all would agree upon is that patients like the idea of laser therapy, even if no clinical advantage to its use can be demonstrated.²² White and colleagues²³ compared scalpel surgery to Nd:YAG laser surgery on patients with probing depths greater than 3 mm, slight inflammation, intact crestal lamina dura, and no radiographic evidence of bone defects. In other words, patients who most probably had early periodontitis. No detailed description was given of the actual surgeries performed, except that they were performed by dentists who were trained in the use of the Nd:YAG laser. Their conclusions were that the Nd:YAG laser produced an equivalent result to scalpel surgery, and that it was less painful and produced less bleeding. In a related study, the histological difference between noncontact and contact Nd:YAG tissue effect was demonstrated²⁴ and corroborates the study demonstrating decreasing transmission in the contact application.²¹ Epstein described the Nd:YAG laser curettage technique as follows:

* Use a 320 m m fiber, 1.5-2.0 W, 15-20 pps;

* Insert to pocket depth and irradiate, keeping fiber parallel to root;

* Move fiber horizontally and vertically for 90 seconds or more;

* Stop when there is fresh blood;

* Local anesthesia is usually not needed.

Cobb and colleagues²⁵ in 1992 noted root damage in all specimens where the Nd:YAG laser was used. In addition, they found residual plaque and calculus remaining in all groups and decreased numbers of live bacteria. This further emphasizes the distinction between killing bacteria and removing the plaque and underscores the question of what relative effect each of these potentially independent variables may have on the final attachment measurements. However, this study was criticized because the fiber was oriented in a perpendicular fashion to the root surface. The critics’ hypothesis was that this perpendicular orientation biased the results to show more damage than in the more clinically relevant parallel orientation. Here, it was presumed that the energy would only strike the root surface at a shallow angle, reducing the risk of root damage. Another study by the same group two years later was performed with the fiber in a parallel orientation to the root surface. Similar results were obtained.²⁶ Root surface damage and decreased fibroblast attachment to the laser-treated surface was found. Furthermore, root planing after laser treatment rendered the root biocompatible again. This suggests that the nonbiocompatible laser-induced damage is shallow and can be removed with root planing.

Gold and Vilardi²⁷ attempted to look at the histology immediately after Nd:YAG laser curettage. While in their legends and text they describe sharp margins with intact nuclei and conclude that the Nd:YAG contact-tip laser can remove sulcular epithelium without collateral damage, their histology shows a remarkable degree of cellular disruption, in one figure extending throughout most of the height and thickness of the tissue. This cellular teardrop-shaped disruption is conceivably the result of deeply scattered and absorbed Nd:YAG laser light. If it were solely from surface heat, one would expect a more radial nature to the distribution of the disruption. Gold and Vilardi²⁷ also noted little evidence of necrosis in the specimens. However, the specimens were taken immediately after laser exposure, and no time for delayed cellular death was allowed. This violated Stanley’s principle of investigating tissue response to irritation. In it, Stanley suggests that multiple teeth be looked at during several postoperative intervals to accurately determine the tissue response.²⁸

In 1995, Henry and colleagues¹³ reported that the argon laser was able to selectively kill bacteria, with pigmented species being more sensitive. Finkbeiner²⁹ performed "selective pocket thermolysis" with an argon laser along with root planing and showed decreases in pocket depth. However, there was no comparison of root planing to root planing and laser. The contribution of the laser to the final result, again, was in question. Wilder-Smith and colleagues³⁰ looked at the effect of the Nd:YAG laser on root surfaces. They found that the Nd:YAG laser could remove the smear layer in certain instances, but that the effect was inconsistent. This corroborates the inconsistency of results with this wavelength in dentin previously documented by Dederich and colleagues.³¹ However, they also found that the intrapulpal temperature increased from 9 to 22 degrees Celsius, and the surface temperature increased from 18 to 36 degrees Celsius. This suggests the existence of a significant thermal threat to the dental pulp posed by the Nd:YAG laser. Radvar and colleagues¹⁴ also investigated the Nd:YAG laser in periodontal pocket therapy, comparing laser alone with scaling and root planing alone. They found that only the root planing group showed a significant reduction in probing depth or bleeding on probing. Both groups showed a reduction in colony-forming unit counts, but only the root planing group sustained the reduction until the sixth week. They concluded that the Nd:YAG laser did not improve the periodontal outcome. Ben Hatit and colleagues¹⁵ looked at the effect of a pulsed Nd:YAG laser on subgingival bacterial flora and the cementum, and compared it to scaling and root planing alone. They found that all laser groups showed reduced live bacterial counts, but that the laser caused root surface damage.

By this time, it seemed clear that removal of debris from the root surface was paramount, regardless of the absence or presence of any added benefit from the laser. So, a natural question to ask was whether the laser removes debris from the root or the pocket. The consensus developed from studying the literature by the American Academy of Periodontology, and quoted from the 1996 position paper,³² was that "there is little evidence that lasers ... have any value in removal of accretions from the root surfaces, nor for any other form of root debridement in vivo."

"The application of Nd:YAG laser to root surfaces results in alterations in root surface protein mineral ratio, affects the ability of fibroblasts to attach in vitro, and alters the nature of the smear layer following conventional scaling and root planing. It is as yet unclear if these surface alterations are beneficial or detrimental.

"The ability of a laser to remove the pocket soft tissue lining or to remove bacterial accumulations are as yet unknown.

"Furthermore, there are no research data that support the use of lasers for subgingival curettage."

Moritz and colleagues¹⁶ looked at the effect of a diode laser (805 nm) in 50 patients and found that it facilitated live bacterial reduction, especially Actinobacillus actinomycetemcomitans In 1997, Cobb³³ cautioned against the use of lasers within the pocket:

"Despite the suggestions that lasers are a desirable alternative to traditional periodontal root instrumentation and the recent FDA [clearance] of the Nd:YAG laser for such an application, numerous peer-reviewed articles concerning in vitro and in vivo results strongly suggest caution with respect to clinical application.

"There appears to be a high potential for laser-induced irreparable physical damage to the root surface"

Moritz and colleagues¹⁷ again looked at the effect of the diode laser, comparing scaling and root planing alone to scaling and root planing followed by laser irradiation. He noted a decreased live bacterial count in those pockets treated with the laser compared to root planing alone. However, no improvement was mentioned in pocket depths or attachment gain.

A consensus report³⁴ was published in 1998 that looked at surgical and nonsurgical pocket therapy. With regard to whether the soft tissue lesion should be surgically removed, the consensus was that "there is no support for the deliberate excision of the soft tissue lesion during periodontal flap surgery, with or without osseous recontouring, in order to reduce or eliminate the periodontal pocket."

Spencer and colleagues³⁵ looked at the effect of CO₂ and Nd:YAG laser exposure with and without surface water cooling on oral soft tissue to the underlying bone. They found the Nd:YAG laser caused far greater increases in temperature (8.0 to 11.1 degrees Celsius) than the CO₂ laser (1.4 to 2.1 degrees Celsius). They concluded: "At energy densities equal or above those reported here, the increase in temperature at the bone surface as a result of periodontal soft tissue surgery with the Nd:YAG laser could be damaging, especially if the exposure is prolonged."

Liu and colleagues³⁶ compared laser to scaling and root planing both alone and in combination with regard to IL1-b response. The degree to which this cytokine is present in the gingival crevicular fluid is closely associated with periodontal destruction. It was found that:

* The laser was less effective than scaling and root planing in reducing IL1-b;

* Inclusion of scaling and root planing had a superior IL1-b response compared to other therapies without it; and

* No additional benefit was found when the laser was used secondary to scaling and root planing.

In another study, histological evidence of severe pulpal damage was presented by Tokita and colleagues.³⁷ They held the Nd:YAG fiber tip stationary against the crown of the tooth and irradiated for 60 seconds at 2.0 W, 20 pps, and 150s pulse width. The histology presented demonstrated holes burned through the pulp and contradicts White and colleagues²⁰ in dramatic fashion in that it depicts the path of direct light penetration and not thermal conduction from the external surface of the tooth. Further dramatic and convincing evidence of the threat of penetrating pulsed Nd:YAG light was presented by Sunakawa and colleagues³⁸ when they used a scanning technique instead of holding the tip stationary. They found massive pulpal damage concomitant with decreased neuronal function (i.e., lack of sensitivity). They also noted that this pulpal damage occurred without any histological change in the dentin, meaning that the damage occurred without the clinician being able to see any change in the dentin. In conclusion, they stated that "clinicians should not use this kind of laser carelessly to desensitize hypersensitive dentin."

Moritz and colleagues¹⁸ found that the pulsed Nd:YAG laser could selectively kill some bacteria after transmitting through dentin, again contradicting the opacity theory of White and colleagues.²⁰ Chen and colleagues³⁹ looked at the effects of pulsed Nd:YAG laser energy on human fibroblasts in vitro. They found that the fibroblasts demonstrated cytomorphologic changes to cell death, the amount of which was proportional to the power settings. They warn of potential damage and suggest minimizing the exposures if this laser is to be used in periodontal soft tissue. Kreisler and colleagues⁴⁰ looked at the effect of the Ga-As laser (810 nm) on human gingival fibroblasts in vitro and concluded: "This laser may cause collateral damage when used for periodontal pocket decontamination. Further research is needed to determine clinically acceptable exposure regimens."

Discussion

Perhaps the most striking feature of the body of literature examining laser curettage is that no evidence exists that documents any improvement in attachment or pocket depths over scaling and root planing alone. This, in reality, should not be surprising since the purported objective of the laser in the first place is to remove the sulcular soft tissue lining, and that has been shown by the periodontal literature to be unnecessary. While there is evidence documenting the bactericidal nature of intrasulcular use of pulsed Nd:YAG laser energy, improvements in periodontal health have not been shown, and may indeed be wishful thinking. There is a preponderance of evidence documenting root damage, pulpal damage, and other forms of collateral damage from pulsed Nd:YAG laser use on the periodontal tissues. This alone should be reason enough to avoid using this laser until there is better information defining the energy thresholds that will avoid clinically significant and irreversible collateral damage to the pulp and periodontium. However, being able to demonstrate acceptable damage control is not sufficient for laser curettage to be justified. Safety must coincide with convincing evidence of benefit to the patient. Unfortunately, even after more than 20 years of promotion of the intrasulcular use of the pulsed Nd:YAG laser,⁴¹ neither is in evidence. Based on the literature presented here, it appears that to use the pulsed Nd:YAG laser for curettage is to introduce risk to the patient with no demonstrable benefit; and this suggests that it is time for the scientific discussion of Nd:YAG laser curettage to expand to include ethical considerations.

Ethical and Legal Considerations

Hippocrates said, "I will follow that method of treatment which, according to my ability and judgment, I consider for the benefit of my patients, and abstain from whatever is deleterious and mischievous."⁴²

Dentists have an ethical obligation to uphold the Hippocratic oath and not create false hopes for their patients. Also, court rulings have required that patients be told about all the risks of therapy and alternatives. This would mean that if the laser is used for curettage or sulcular debridement, the patient needs to be aware that there might be damage to the root, bone, soft tissue, and pulp with no demonstrative clinical benefit. It is also unethical to claim the laser will disinfect tissue or prevent bacterial infection when the FDA clearly stated that these claims and claims of Nd:YAG laser for excisional new attachment procedure were not permitted.⁴³

In promoting "laser assisted periodontal therapy," one should use randomized blinded controlled longitudinal clinical trials, or longitudinal studies or case-controlled studies⁴⁴ and not uncontrolled case reports and hearsay evidence. Until the appropriate evidence-based studies are published and there remains a possibility of damage to the patient, dentists and dental auxiliaries should be discouraged from using the Nd: YAG or comparable laser in the region of the sulcus or periodontal pocket because it may be difficult to defend such damage in a court of law.⁴⁵

Conclusion

Laser curettage following scaling and root planing, like traditional curettage, adds no benefit or improvement. The reported decrease in sensitivity that contributes so much to its popularity may well be due to pulpal damage. Damage to the root and periradicular tissues by the laser is a common result of laser curettage. In view of the documented risk of collateral damage and lack of added value, there is no reason to use the pulsed Nd:YAG laser for intrasuclular pocket therapy.

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To request a printed copy of this article, please contact/Douglas N. Dederich BSEE, DDS, MSc, PhD, Department of Periodontics, LSU School of Dentistry, 1100 Florida Ave., Box 138, New Orleans, LA 70119-2799.