Superpulsed, Dual-Wavelength Diode Laser Technology
Do the shortest pulses at the highest energy density achieve the best results?
Robert D. Levine, DDS | Scott Myers, DMD | Arthur Levy, DDS
Diode laser technology has been available to the dental profession for at least 20 years.1 Manufacturers have produced lasers in wavelengths ranging from 810 nm to 1,064 nm,2 and they make a variety of claims as to why their wavelength is the best. These lasers work in several modes, including continuous wave and a few different gated modes.3 Depending on the model, maximum peak power can range from 2 W to as much as 7 W.
Diode lasers can only cut when their fiber tips are carbonized (ie, activated). Because their particular wavelengths have a very low coefficient of absorption for pigmentation,4 the only way that cutting can be achieved is through the generation of heat at the tip of the fiber. Therefore, when a diode laser is functioning with carbonization, it can be more realistically described as a hot tip cutting instrument as opposed to a true laser.5 Only a laser with photons that are absorbed by a specific chromophore for the wavelength can be considered a true cutting laser.6
Temperature variability is always an issue when utilizing classic diode lasers. A hot tip can produce temperatures ranging from 100°C to 5,000°C. Although varying degrees of collateral thermal damage can occur, these are still very functional tools that are far superior and safer when compared with electrosurgical instrumentation.7
Modes and Power Levels
Lasers can work in a variety of modes. In continuous wave mode, the energy is being released nonstop. Gated modes mechanically or electronically regulate the energy and can be shut off in increments of 0.25 seconds to 0.5 seconds. In free-running pulsed mode, the energy is emitted at extremely high peak powers of 1,000 W or more in microseconds, followed by a tremendous amount of relaxation time before the next pulse to allow for cooling. Lastly, in the superpulsed mode, the energy is applied in milliseconds.8
Superpulsed laser technology has been applied to both diode lasers and 10, 600 nm CO2 lasers. CO2 lasers are noncontact lasers absorbed by water, whereas dual-wavelength diode lasers are contact lasers absorbed by pigmented tissue. However, all diode wavelengths have a minimal capacity to be absorbed by water containing tissue.9 Most CO2 lasers operate at a high peak power with some in the range 120 W of energy density. The pulse duration of time is in milliseconds, and thermal relaxation (ie, pulse spacing) allows for minimal charring and adequate cooling of the tissue before the next pulse. By comparison, diode lasers can have a peak power of up to 20 W. The ability to superpulse is the only similarity between these two laser technologies.10
When the coagulation performance of an 810 nm diode laser is compared with that of a 980 nm diode laser using pure photon energy and a nonactivated tip, it can be seen that the coagulation level is nearly doubled by the use of the 810 nm wavelength.11 However, when the ablation performance of these wavelengths is compared, we find that the ablation level is nearly doubled by using the 980 nm wavelength.12 It should be reiterated that in order to cut tissue efficiently with any diode wavelength, the tip must be activated due to the weak coefficient of absorption of the pigment. The tips provided with these lasers are either preactivated to allow for the consistent cutting of tissue or nonactivated. With respect to coagulation levels, use of an activated tip results in coagulation that is 5 times greater than use of a nonactivated one.13
So, what happens when both wavelengths are combined? According to histologic studies conducted by Ostler and colleagues,11 an ideal balance of coagulation and ablation is achieved. The benefit of a dual-wavelength diode laser (Gemini® 810 + 980 Diode Laser, Ultradent Products, Inc.) comes from the combined use of both wavelengths to provide a greater effect on the tissue while delivering less energy. To prevent collateral damage to the tissues, the goal of laser treatment has always been to do the selected work using as little energy as possible.
As mentioned earlier, the ability to cool the tissue is paramount to the success of this treatment. Cooling can be accomplished through the effects of superpulsing. This technology creates a dynamic wherein the tissue absorbing the laser energy is afforded adequate time to cool before the next onslaught of laser energy is delivered. In this process of pulse spacing, it is preferred to have a longer period of time occur between pulses than the period of time allowed for the duration of the energy pulse itself.14 This timing is critical and the main component that makes superpulsing technology so unique.
For example, if a dual-wavelength laser is emitting energy in the superpulsed mode at 20 W peak power, and for every second of use the laser pulses 50 times, there is a 20-millisecond package of time for each pulse. The duty cycle is defined as the amount of time per cycle that the laser is on and delivering the pulse. Therefore, during this 20-millisecond package, if the laser energy is being delivered for 4 milliseconds followed by a pause of 16 milliseconds, the average power would be 4 W/second and the duty cycle would be 20%.
So, how does all of this affect the determination of which wavelength to use? Because the dual-wavelength laser combines two wavelengths with individual powers of 10 W for a combined peak power of 20 W, when compared with a single-wavelength laser at a peak power of 10 W, the dual-wavelength possesses double the energy density, which allows for a shorter duty cycle and a longer relaxation time for cooling during the 20-millisecond cycles. Because a higher energy density is being applied, cleaner and faster surgical cuts can be accomplished with less potential for charring.
When performing laser treatments, the best results can be achieved with the least risk of unwanted thermal damage by using a very short pulse at the highest possible energy density for the shortest possible time.15 Laser technologies are constantly evolving to improve performance and safety. When used with the proper training, diode lasers are great cutting and coagulation tools, and the dual-wavelength diode technology might offer even greater benefit to practitioners.
About the Authors
Robert D. Levine, DDS
Director of Laser Dentistry
Arizona School of Dentistry & Oral Health
Global Laser Oral Health, LLC
Scott Myers, DMD
Arizona School of Dentistry & Oral Health
Arthur Levy, DDS
Arizona School of Dentistry & Oral Health
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