Oral Health Group
Feature

Scientific Data Leads to Informed Choices

Scientific Review of Significant Parameters in the Search for Optimal Laser-Tissue Interaction of an Erbium-family Laser System


September 1, 2005
by Guylaine Raymond, DMD

Introduction

With the prevalence and utility of Erbium-family laser systems on the market, inconsistencies in reporting specifications leaves some room for interpretation and very speculative explanations. The primary goal of this discussion is to report scientific-based results on pulsed laser parameters of the most popular erbium-family laser systems so that dentists can make informed choices when purchasing a laser system capable of cutting human hard tissue, soft tissue and bone.

Abstract

Vogen and Venugopalan1 recently published a study that measured and compared parameter values of three individual laser systems in an attempt to establish the theoretical optimum. Among the parameters highly responsible for quality and efficacy of laser-tissue interactions1,2 are pulse energy, pulse repetition rate, average power, pulse width, temporal pulse shape and beam profile at the outcoupling end of the hand piece. Their report examined three erbium-based laser systems3 from three leading manufacturers of these devices: Laser 1 in the study is the erbium, chromium:yttrium, scandium, gallium, garnet laser (Er,Cr: YSGG); laser 2 is an erbium:yttrium, aluminum, garnet laser system (Er:YAG), as is laser 3. Both Er:YAG lasers were from two different manufacturers. After collecting real field data and comparing physical characteristics of pulsed radiation, it became clear to the authors of the study that no erbium-based laser system can be compared to another simply based on front panel parameter settings only.3

RESULTS

Pulse energy and average power

Flash lamps have no consistent emission intensity due to the fluctuation of the Xenon lamp in the laser. Consequently the emitted pulse energy would vary. In addition, pulse repetition rate (PRR) fluctuated about 3% to 5% where adjustable.

The outcoupled average power also differed from values at the control panel:

54.14% less (Laser 3)

18.17% less (Laser 2)

5% to 20% difference rising with increasing pulse energy, overall lower discrepancy (Laser 1)

Losses also depended on the kind of sapphire tip used. (It should be mentioned that Laser 3 in the study had severe mechanical design flaws such that sapphire tip would not attach to the hand piece.)

Pulse width

Heat transfer from the laser delivery system to the target tissue is influenced by pulse duration as well as the pulse shape, width of pulse base, and the rise time of the pulse.

A study published by Stral et al,3 shows that the only laser not causing thermal transfer at higher pulse energies was Laser 1, even when the overall power of the laser was reduced by 20%. The pulse rise time (the time it takes for the pulse to reach peak power) was also 8.5% shorter than Laser 2 and Laser 3, and had the shortest pulses of average 91 s. A faster, more efficient, more intense pulse is ideal for clinical dentistry since a longer, lazier pulse profile results in excessive amounts of laser energy being absorbed by the target tissue, which can have negative effects on the tissue.

Looking at temporal pulse shape [Figure 1], Laser 1 shows a fast rise to maximum, followed by a fast, immediate, exponential drop of the curve.

DISCUSSION

Pulse duration

At constant pulse energy, Laser 1 with a pulse duration of 90 s is expected to have the highest ablation efficiency and the lowest thermal impact on surrounding tissue.

Pulse shape

The faster the pulse rises, the faster the energy is deposited in the irradiated material and the better it stays confined. After reaching its maximum, the pulse should decay very rapidly to avoid further heating of tissue after ablation.

Laser 1 has the steepest leading edge, and after reaching its maximum drops quasi-exponentially.

Based on the pulse shape, Laser 2 is expected to have the lowest ablation efficiency and greatest thermal impact, caused by the large pulse width, the slow rise time and the long decay time.

Laser 3 rates better but because of the long pulse duration, the objective pulse ablation efficiency might not be optimum.

Laser 2 and 3 would tempt users to choose higher pulse energy with damage to residual tissue, and both would be expected to have higher thermal impact at same pulse energy and average power.

CONCLUSION

Laser 1 has the best relative results3 in terms of pulse width and pulse shape for efficient hard tissue ablation, although the trailing edge of the pulse contains the highest energy. The main advantage of short pulse duration and short rise time is a high pulse peak power and well confined energy distribution in tissue.1

REFERENCES

1. Vogel A., Venugopalan V. Mechanisms of Pulsed Laser Ablation of Biological Tissues. Chem Rev 2003; 103:577-644.

2. Meister J, Apel C, Franzen R, Gutknecht N. Influence of the Spatial Beam Profile on Hard Tissue Ablation, Part I: Multimode Emitting ER:YAG Lasers. Lasers Med Sci. 2003; 18:112-118.

3. Stral M, blacker B, Bcker A, Beer F, Moritz A, Wintner E. Comparison of the Emission Characteristics of Three Erbium Laser Systems – A Physical Case Report, J Oral Laser Appl 2004; 4: 263-270.

Dr. Guylaine Raymond maintains a private practice in Gatineau, Qubec, Canada. She has been practicing laser dentistry since 2002, and uses both the Er,Cr:YSGG laser wavelength, as well as the diode laser wavelength each day.

NORTH AMERICAN SURVEY OF LASER DENTISTS REVEALS SURPRISING TRENDS

A recent survey on laser dentistry by one of North America’s most widely read trade publications indicates that both practitioners and patients are satisfied with laser technology. Also, patients are enthusiastic about laser treatment because many procedures do not require anesthesia. Dentists are also pleased about its ever-growing number of applications.

Redefining the dental experience

As dentists, all of us have a sincere desire to make patients happy by improving their “in-chair” experience. Patients often feel anxious when visiting the dentist. Dentists universally report that they would be happier if their procedures could significantly improve their patients’ experience.

Laser dentistry has fundamentally transformed the dental experience for myself and my patients. Like many others, I am convinced this transformation has dramatically enhanced patient comfort and dentist satisfaction. The key to this has been the improvement of laser technology, a technology that has delivered on its promise. My procedures now require less anesthesia with minimal to no discomfort in most cases, less invasive and more comfortable than traditional methods. I use lasers each day and perform a wider range of procedures than ever before. My patients like the way I have transformed their dental experience. I feel more appreciated and satisfied, I’m finding new enjoyment in my work, and have been able to diversify my practice.

More procedures than ever

With so many FDA-approved indications for use from Er,Cr:YSGG laser and continuing exploration of new applications such as crowns and veneer prep, treatment of failing implants, placement of implants, sinus augmentation, and so on, laser dentistry with the Er,Cr:YSGG laser offers the widest range of applications across all disciplines. This versatility is reflected in the survey: 90 percent of those surveyed perform up to 10 laser procedures per day, while another eight percent perform 11 to 20 per day.

Increased productivity

The dentists surveyed also stated that a laser system allowed them to address the clinical needs of patients and perform a greater number of clinical and cosmetic procedures, as well as branch into new treatments and procedures not previously offered in day-to-day practice. This resulted in an increase in income and productivity.


Technology like never before

While lasers have been used in dentistry for more than 20 years, until recently no single laser has been cleared for and can be used on all oral tissues. This all changed with the introduction of the YSGG laser. No other instrument in dentistry has the versatility and clinical utility of this device.

With a specific wavelength of 2,780 nanometers and a patented technology as hydrophotonic which uses water molecules energized by laser energy, it is an excellent tool for cutting enamel, dentin, bone and soft tissue.

This was evident in the March 2005 laser survey, which reported that laser use for hard/soft tissues was 95 percent for caries removal/tooth preparation 88 percent for excisional/ incisional surgery, followed by 87 percent for cosmetic gingival contouring and 74 percent osseous crown lengthening.

More laser dentists than ever

Laser dentistry has dramatically improved the cutting efficiency of hard tissue, and the percentage of dentists who use it to perform caries removal/tooth preparation has risen to 95 percent, compared to 54 percent in 2003. The ADA recently reported that at least 82 percent of patients think it “somewhat important, important, or very important” for a dental office to have a laser.

Both groups are enthusiastic about the enormous benefits of laser dentistry, including its dramatic reduction in the need for injected anesthesia (SHULKIN, 1991) and its increasing number of applications. Lasers are no longer considered a niche tool for only the most cutting-edge dentists. This has been illustrated by growing patient demand and the fact that 95 percent of laser users are GPs.

Why use a laser? Eighty-eight percent of respondents said they acquired a laser to take advantage of its clinical benefits.