Method and Dosimetry for Thermolysis and Removal of Biofilm in the Periodontal Pocket With Near-Infrared Diode Lasers: A Case Report
Written by Eric Bornstein, DMD Thursday, 31 March 2005 19:00
Although a number of laser-based techniques have been proposed for “bacterial decontamination” of the periodontal pocket, relatively few studies in the literature address this topic directly. Given the current understanding of the etiology of periodontal disease, a need exists to explore the inherent thermal properties of inexpensive, near-infrared continuous wave (CW) diode lasers as a possible approach to biofilm elimination within the periodontal pocket. A CW diode laser is comparable in temporal emissions to a light bulb, as the laser begins emitting light when it is turned on and persists at a uniform power until it is turned off. These inexpensive lasers are very different from the free-running pulsed (FRP) lasers that are capable of generating very high “peak powers” in very short time periods (one/one-millionth of a second) that are generally referenced in the periodontal literature.
In the case report in this article, a method of live biofilm targeted thermolysis (LBTT) was performed using a CW 830-nm diode laser. LBTT is a different laser technique and employs a different dosimetry and logic than both laser sulcular debridement with a FRP Nd:YAG laser and bacterial photosensitization with a photosensitizer coupled to a (soft) low-level red laser. The LBTT procedure utilizes methylene blue as a heat sink to achieve thermolysis and coagulation of the biofilm. This is accomplished utilizing the secondary quantum optical and thermal emissions from a carbonized, near-infrared diode laser delivery fiber, otherwise known as a “hot tip.” With this novel approach of exploiting the incandescent hot tip’s radiant energy (ie, its optical and thermal emissions), the physical nature of the targeted biofilm in the periodontal pocket is changed from a mucinous liquid-gel to a semisolid coagulum, which then facilitates its removal from the affected pocket with mechanical periodontal procedures (scaling and root planing).
The term “biofilm” describes a community of bacteria enclosed within their own mucinous, gel-like polymer secretions. In the oral cavity, biofilms are responsible for periodontal and peri-implant disease.1 In periodontal disease, the biofilm complex that is attached to the dental root and pocket epithelium protects pathogenic bacteria from exogenous assault (eg, from antibiotics) and endogenous attack from the host’s inflammatory and immune responses, including complement activation, chemotaxis by phagocytic cells, and degranulation of polymorphonuclear leukocytes.2 The unique protective properties of the periodontal biofilm are due in part to the secluded nature of the ecological niche in which the bacteria and biofilm live (the periodontal pocket), making definitive treatment of periodontal disease difficult. Periodontal treatment usually includes physical, antimicrobial, and chemical approaches to eliminate or reduce the biofilm.1
Two laser therapies that have previously been employed and studied to treat periodontal disease in a nonsurgical manner are laser sulcular debridement with a FRP Nd:YAG laser3-5 and bacterial photosensitization with a (soft) low-level red laser and various photosensitization agents.6-10 LBTT utilizes a CW near-infrared diode laser and has fundamentally different dosimetry parameters and logic than both of the aforementioned laser methods. LBTT is a procedure that specifically targets the live biofilm in the periodontal pocket with a heat sink, leading to thermolysis and the biofilm’s facilitated removal.
Laser Dosimetry Management for the Periodontal Pocket
From a dosimetry perspective, the closest treatment corollary to LBTT with a CW diode laser is the laser sulcular debridement procedure, traditionally accomplished with the free-running pulsed Nd:YAG laser. In 1992, Myers suggested specific dosimetry computations for the periodontal pocket with the Nd:YAG laser, and his work generated a laser dosimetry table based on the probing depth of each pocket.11 This general principle and formula were used to generate data with a FRP Nd:YAG laser that led to the first FDA market approval for “laser sulcular debridement.” The specific language included “The removal of diseased or inflamed soft tissue in the periodontal pocket to improve clinical indices including gingival index, gingival bleeding index, probe depth, attachment level and tooth mobility.”11,12
|Table 1. “Light Dose” Calculations for FRP Nd:YAG.
(1) light dose = laser energy delivered to treatment site
(2) (average power [watts]) x (duration of treatment [seconds]) = J (total energy/pocket)
(3) J (total energy/pocket) / (pocket depth [mm]) = J/mm (pd)
|Table 2. Clinical Steps in the FDA-Approved LANAP Procedure With a Free-Running Pulsed Nd:YAG Laser.
(1) Chart probing depths.
(2) Laser troughing with short-duration pulse (a step-down approach) in the pocket until epithelial lining debris ceases to accumulate on fiber tip
(3) Scaling and root planing (with piezo-electric scaler and hand instruments)
(4) Second pass with Nd:YAG laser using a longer pulse duration (635 µs).
(5) Gingival tissue compressed to aid in clot formation with splinting of teeth and occlusal trauma relief as indicated
Gregg and McArthy13 took the periodontal pocket laser dosimetry concept further and cited the first case reports of sulcular debridement utilizing a computation for “light dose” to define the “quantity of laser energy delivered to the treatment site” (Table 1). This novel measure (J/mm of probing depth) was stated by Harris11 to be similar to the value of a drug dose (mg/kg body weight), in that the total light dose would define the concentration of laser energy at the treatment site (the periodontal pocket), much as drug dose defines the concentration of a drug in the tissues. Harris concluded that “light dose” is a useful way to allow comparison of different laser systems examined in similar studies.11 Most recently, Harris, et al14 published a retrospective analysis of the recently FDA-approved laser-assisted new attachment procedure (LANAP), where the light dose delivered was 10 to 15 J/mm of probing depth. Yukna, et al15 reported histologic evidence of periodontal ligament reattachment and regeneration in the absence of a long junctional epithelium following the LANAP procedure. The primary goals of LANAP include debridement, removal of pocket epithelium and underlying in-fected tissue within the peri-odontal pocket, and removal of calcified plaque and calculus adherent to the root surface (Table 2).14 Further-more, Harris has estimated (from other studies) that a “toxic dose” of light energy with the pulsed Nd:YAG laser that would potentially damage root surfaces would be in the range of 20 to 60 J/mm of probing depth. Further, he concluded that a different dosimetry needed to be developed that is appropriate for each unique laser modality.11
PULSING ABILITIES OF THE ND: YAG AND CW DIODE LASERS
A FRP Nd:YAG laser is capable of pulse durations in the millionths of a second (10-6 second), which allow for high peak powers (1,000 to 2,000 W/pulse). This allows safe and rapid ablation of sulcular epithelium in a periodontal pocket.14 A clinician using a FRP Nd:YAG laser for sulcular debridement can apply an intense burst of laser energy for a very short time interval to the sulcular epithelium. This will cause quick (10-6 second) and precise ablation of the epithelial tissue, as the ablation front of the laser tissue reaction remains ahead of the thermal front. A CW or gated diode laser placed in the periodontal pocket does not have the high peak power or microsecond pulse capability of the FRP Nd:YAG laser. A CW diode laser has far longer pulse durations (10-3 or thousandths of a second) with far less peak power that will not reach the ablation threshold in soft tissues.16,17 As such, a CW diode laser requires a fundamentally different logic and dosimetric approach for closed (periodontal pocket) procedures. This is due primarily to the fact that the output power of the laser is converted to heat and radiant energy from what is known as the “hot tip.”16,17
Considering the physical pulse limitations of a CW diode laser, the calculations for this device when used in the periodontal pocket should be substantially different from the recently published LANAP approach with a FRP Nd:YAG laser. This important distinction is vital for a clinician to understand. The inherent physical and photobiological differences between the diode laser and the FRP Nd:YAG laser (ie, diode “hot tip” contact vaporization versus Nd:YAG ablation) allow for far smaller margins of error with the diodes due to the substantial heat production at the incandescent tip.17 Following Harris’ suggestion of requiring a quantitative value for a “light dose” for each laser modality,11 a new set of parameters may be defined, with the implementation of different dosimetric values and logic explicitly tailored to the CW diode laser in closed periodontal pocket procedures. These para-meters, referred to as diode laser pocket parameters (DLPP), will exploit the diode laser’s characteristics of an incandescent tip in the periodontal pocket while also producing a measure of safety against burning and injuring adjacent tissues as a result of excessive heat, power, and/or treatment time.
CREATION OF THE “HOT TIP” WITH CW DIODE LASERS
The physical changes in quantum emissions and photobiology that will instantaneously occur when a diode laser fiber (dispensing greater than 500 mW of energy) comes into contact with tissue and carbonizes the tip of the fiber have been described in detail.17 Upon carbonization of a diode laser fiber tip, an immediate and profound change occurs in the quantum emissions radiating from the fiber in the form of thermally induced incandescence.
The First Law of Thermo-dynamics states that energy is neither created nor destroyed; it simply changes form. The application of this law with the CW diode laser in the periodontal pocket is that the electromagnetic energy of the laser beam is absorbed by the carbonized tip, whereupon it vibrates the molecules in the tip and is converted to heat energy. As the tip instantaneously becomes hotter (above 726ºC), the heat is reconverted into electromagnetic energy in the form of incandescence, and the tip then emits radiant visible and infrared light and is now “red hot.”18,19 This resulting secondary quantum emission causes fundamentally different heat transfer and photobiologic events in the periodontal pocket and tissues than would be seen with the diode laser’s primary infrared photons.17
|Figure 1. Incandescent tip in a pocket.||Figure 2. Incandescent bacterial transfer loop in a Bunsen burner.|
The photobiology of these changes can be partially explained by the Second Law of Thermodynamics, which states that as the primary energy of the laser is converted from one form into another, some of the energy becomes unavailable for further use. This does not mean that some of the laser energy is destroyed, but rather that a portion of the energy in the transfer becomes “waste energy” in a diffuse form (in this example, heat) that cannot be used for the same work as the primary photon energy. It can be said that this “heat” or “waste energy” from the hot tip is of a lower quality than the primary photons from the laser, as the laser’s primary photons are well collimated and focused as they are emitted directly from an uncarbonized fiber.19,21 As the diode hot tip begins to glow with heat (Figure 1), it emits first red and then orange visible light. This can be seen as the tip reaches 900ºC to 1,200ºC.19 Another representation of this energy conversion phenomenon can be observed with a bacterial transfer loop heated to approximately 1,000ºC in a traditional Bunsen burner (Figure 2).
With the hot tip and degraded fiber optics, the forward beam quality and emissions of primary infrared photons from the laser (measured in terms of energy, focusability, and homogeneity) are substantially reduced and cannot continue to deliver high-quality energy efficiently to the deeper tissues.18 These quantum changes ob-served with CW diode lasers are generally not understood or taken into account by clinicians and have been well described by Verdaasdonk and Swol20 and Janda, et al.21 Hence, the dosimetry computations for the closed-pocket FRP Nd:YAG sulcular debridement procedures described by Harris do not adequately reflect the thermal events seen with the diode lasers, as the physics, emissions at the tip, and photobiology are different.11 DLPP will address these differences with changes in output power, total energy, and treatment time to achieve the unique goal of biofilm thermolysis.
ENERGY TRANSFER DIFFERENCES BETWEEN THE FRP ND:YAG AND CW DIODE LASERS
The power density equation for ablation with the FRP Nd:YAG laser in the periodontal pocket measures the potential thermal effect of the laser photons at the irradiation area:
|power density = (W/cm2) =||
laser output power (W)
|beam diameter (cm2)|
However, with the CW diode laser, significant amounts of power that are converted to local radiant heat at the carbonized fiber tip damage the fiber optics and eliminate any defined beam area. This heat (from the tip) is then transferred to the proximal periodontal tissues via contact thermal conduction.17,18,20-22 Thermal conduction is a fundamentally different mechanism and manner of energy transfer to the tissues than is seen with a FRP Nd:YAG laser, which is capable of producing substantial forward power transmission out of the fiber, thereby achieving tissue ablation. Ablation occurs when the Nd:YAG laser deposits high peak power energy into a small tissue volume directly under the delivery tip in a short period of time (millionths of a second). This rapid and contained energy transfer produces the biomechanical work of ablation.22 Most of the laser pulse is transmitted directly into the tissue under the tip, where the laser energy quickly ablates the tissue in a far more energy efficient manner than is seen with contact vaporization (via heat conduction) from a CW diode laser. Furthermore, the high peak power pulses of the FRP laser most likely assist in the ablation and removal of any debris and detritus caught on the Nd:YAG fiber tip, which would otherwise block the forward laser emission and build up unwanted heat in the fiber.22 Conversely, the CW diode is generating large amounts of incandescent radiating heat energy in all directions as the output power of the laser is largely converted to heat. This leads to a marked difference in the laser-tissue interaction (thermal contact vaporization versus ablation) seen with the different lasers.17,22
TREATMENT TIME—VITALLY IMPORTANT WHEN CW DIODE LASERS ARE USED IN THE PERIODONTAL POCKET
|Table 3. Laser Dosimetry Calculations.
The output power of a laser device refers to the number of photons emitted from the laser at a given wavelength and is measured in watts (1 W = 1,000 mW).
The power density of a laser beam measures the potential thermal effect of laser photons at the treatment irradiation site/area of tissue. Power density is a function of output power and beam area and is calculated in (W/cm2). The value is obtained with the following equation:
The total energy delivered into a tissue area by a laser system operating at a particular output power over a certain period of time is measured in joules and is obtained with the following equation:
(2) total energy (J) = laser output power (W) x time (s)
It is essential to know the distribution and allocation of the total energy (J) delivered into a given tissue area in order to correctly measure tissue site dosage for maximal beneficial tissue response. Total energy distribution will be measured as energy density in (J/cm2).
The energy density is a function of power density and time (s), is measured in (J/cm2), and is calculated as follows:
(3) energy density (J/cm2) = power density (W) x time (s)
Usually, (without a hot tip) to calculate the treatment time to deliver a dose of laser energy to a given volume of tissue, a clinician will need to know either the energy density (J/cm2) or total energy (J), as well as the output power (W) and beam area (cm2). Treatment time can then be calculated with the following equation:
However, because of the “hot tip” phenomenon with diode laser fibers in a closed environment (ie, the periodontal pocket), there is no actual value for beam area, and hence, there is no practical power density and/or energy density equation. Therefore, treatment time must rely on equation 4a for “light dose” parameters with the CW diode laser within the periodontal pocket.
When considering the radiant heat from the incandescent tip seen with a CW diode laser, the traditional dosimetry equations and logic for closed-pocket procedures with the FRP Nd:YAG laser must be altered and considered clinically in terms of treatment time. This conversion of clinical thought and practice will prevent unwanted thermal tissue damage. For example (as noted in Table 2), laser troughing (in LANAP) should continue in the periodontal pocket with the FRP Nd:YAG laser independent of time and until epithelial lining debris ceases to accumulate on the fiber tip. This sulcular debridement procedure is accomplished safely at an average output power of 4 W and 150-µs pulse durations. However, with the incandescent tip of a CW diode laser, a clinician could safely use the CW system at a 4-watt output for only 1 to 2 seconds before the proximal periodontal tissues would be irreversibly injured and burned. Hence, this laser troughing logic and dosimetry for the FRP Nd:YAG laser cannot be used with the CW diode laser, as the 4-watt output power will cause a larger amount of energy to be converted to local heat at the fiber tip. The calculations needed for laser dosimetry with the FRP Nd:YAG and CW diode lasers are explained in Table 3.
With the direct energy conversion (to heat) of excess power from the CW diode laser, more heat from the fiber tip would be transferred through conduction to the proximal periodontal tissues. From Table 3, it can be seen that by changing the approach to closed (periodontal pocket) debridement with CW diode lasers, specifically adapting to a concern for treatment time (equation 4a, Table 3), a new “light dose” logic can be created with dosimetry parameters that apply to the pocket based on time. Furthermore, because of the intense heat of the incandescent tip, additional clinical modifications to ensure safety and minimal tissue damage will include lowering the total energy delivered into a closed pocket. These specific alterations are necessary because (as previously described) the CW diode laser does not have a “beam area” for the incandescent hot tip. Without a defined beam area, there can be no practical power density or energy density equation to determine a valid light dose, which is defined as the primary laser photons delivered to the treatment site directly under an undamaged fiber tip.
Altering the value of total energy in order to use the CW diode laser safely in the periodontal pocket is accomplished by decreasing the laser output power (equation 2, Table 3) to about one third of that published for the FRP Nd:YAG laser when used for sulcular debridement procedures such as LANAP.14 These alterations will satisfy the requirement of Harris for developing a new quantitative dosimetry that is appropriate to each laser modality11 and can be termed diode laser periodontal parameters. This can be easily visualized by converting the traditional total energy equation in Table 3:
EQUATION RESTRUCTURE FOR DLPP
(1) total energy (J) = laser output power (W) x time (s)
|(1a) treatment time (s) =||
total energy (J)
|laser output power (W)|
Utilizing this equation (1a), a clinician can change both laser output power and/or treatment time to ensure maximum safety and success with a CW diode laser used in a closed periodontal pocket. Hence, it is seen with DLPP that the output power that is safe and efficacious for closed intrasulcular procedures with the FRP Nd:YAG laser (average 4 W) would be approximately 3 times greater than should be safely used with the CW diode laser (1 to 1.2 W). In addition, since an intrasulcular procedure with the FRP Nd:YAG laser is performed independent of time (ie, until epithelial lining debris ceases to accumulate on the fiber tip), it has been determined (through clinical trial and error) that CW diode procedures in the closed environment of the pocket should be completed in approximately 20 to 25 seconds with rapid tip movement to prevent unwanted thermal damage to proximal periodontal tissues.
PEAK POWER—THE PARAMETER GOVERNING CONTACT VAPORIZATION VERSUS ABLATION
|Table 4. FRP Nd:YAG Peak Power Calculation for a Typical LANAP Procedure.
Average output power (W) / rep rate (Hz) / pulse duration (µs) = peak power/pulse (W)
Laser parameters: 150-µs pulse duration, at 25 Hz, and 3.9 W average power (3.9 W) / (25 Hz) / 150 µs (.000150) = peak power/pulse (1,040 W/pulse)
Described as a function of energy per pulse:energy per pulse = 1,040 W/pulse x 150 µs (.000150) = .156 J/pulse or 156 mJ/pulse
Described as a function of energy per second:energy per second = .156 J/pulse x 25 pulses/s = 3.9 J/s delivered to the pocket
Therefore, to obtain total energy delivered to pocket:3.9 J/s x 30 seconds treatment time = 117 J delivered to pocket in 30 seconds.
Finally, to obtain energy delivered in an 8-mm pocket (J/mm/pd):117 J delivered to pocket / 8-mm pocket = 14.6 J/mm/pd for 30 seconds treatment time.
|Table 5. CW Diode Power Calculation for Comparison to FRP Nd:YAG.
Laser parameters: CW output for 30 seconds at 3.9 W average power
To express as total energy delivered to pocket:
3.9 W x 30 seconds = 117 J (identical total energy as the FRP Nd:YAG)
Described as a function of energy per second:
117 J / 30 seconds = 3.9 J/s (identical energy/second as the FRP Nd:YAG)
3.9 W CW is also the peak power value for the diode laser where (in Table 4) 1,040 W/pulse is the peak power per pulse—or the power available for the work of ablation for the FRP Nd:YAG laser at a pulse duration of 150 µs (.000150 sec)
Therefore the CW diode laser has the following:
3.9 W / 1 second = 3.9 W constant peak power or power available for the work of ablation in a one-second delivery to the pocket