Free-electron laser and heat-conducting templates: a study of reducing cutaneous lateral thermal damage

Evaluation of irradiation effects of near-infrared free-electron-laser of silver alloy for dental application

In the application of lasers in dentistry, there is a delicate balance between the benefits gained from laser treatment and the heat-related damage arising from laser irradiation. Hence, it is necessary to understand the different processes associated with the irradiation of lasers on dental materials. To obtain insight for the development of a safe and general-purpose laser for dentistry, the present study examines the physical effects associated with the irradiation of a near-infrared free-electron laser (FEL) on the surface of a commonly used silver dental alloy. The irradiation experiments using a 2900-nm FEL confirmed the formation of a pit in the dental alloy. The pit was formed with one macro-pulse of FEL irradiation, therefore, suggesting the possibility of efficient material processing with an FEL. Additionally, there was only a slight increase in the silver alloy temperature (less than 0.9 °C) despite the long duration of FEL irradiation, thus inferring that fixed prostheses in the oral cavity can be processed by FEL without thermal damage to the surrounding tissue. These results indicate that dental hard tissues and dental materials in the oral cavity can be safely and efficiently processed by the irradiation of a laser, which has the high repetition rate of a femtosecond laser pulse with a wavelength around 2900 nm.

Controlling thermal damage of incisions using diamond, copper, and sapphire heat-conducting templates with and without cooling

INTRODUCTION

We investigated the reduction of thermal damage to the surrounding tissue when laser incisions were made with and without using thermal conducting templates at room temperature and cooled to 5 degrees C.

STUDY DESIGN/MATERIALS AND METHODS

We used the Vanderbilt free-electron laser (FEL) at 5.4, 6.1, 6.45, and 7.7 microns. We also used a conventional continuous wave (CW) carbon dioxide laser at 10.6 microns. Incisions were made on 5x10 mm pieces of human breast skin (in vitro) and analyzed with histology. Computer morphometrics were used to measure the amount of thermal damage.

RESULTS

All templates produced a statistically significant reduction in the thermal damage. Additionally, we showed that cooling the templates made a statistically significant greater reduction in the thermal damage. The cooled diamond template reduced the thermal damage from the FEL to 28% of the damage observed without a template. The same cooled template reduced the thermal damage from the CO(2) laser to 56% of the damage observed without a template. Lesser reductions were observed with the copper template and even less with the sapphire template. The sapphire template reduced the thermal damage to 39 and 67% of the damage observed without a template for the FEL and the CO(2) laser, respectively.

CONCLUSION

These results indicate that unwanted lateral thermal damage from laser incisions can be reduced with cooled thermally conductive templates with the best results obtained with the diamond template, which is also the best thermal conductor.

Wound healing of 6.45-microm free electron laser skin incisions with heat-conducting templates

We have previously shown a reduction in lateral thermal damage with acute studies of skin incisions made in vitro using heat-conducting templates. Here we examined the wound-healing response to laser incisions with heat-conducting templates and explored the use of an optically transparent template with the free electron laser (FEL) at 6.45 microm. First we evaluated the effects of a sapphire heat-conducting template on the lateral thermal damage of FEL incisions using in vitro human skin samples. Next we compared wound tensile strength and histological scoring of the healing of incisions created on the dorsal pelts of live rats with the FEL utilizing metal and sapphire heat-conducting templates and scalpel incisions. The animals were euthanized and the wounds were analyzed at postoperative days 7, 14, and 21. The depth and lateral thermal damage of FEL incisions on in vitro human skin were significantly reduced with the sapphire heat-conducting template. Nonstatistically significant differences in wound tensile strengths and histological scoring of wound healing were noted at days 7 and 14. By day 21, all of the incisions appeared similar. When the data from days 7 and 14 were combined, statistically significant differences were found for each of the templates (except the histological evaluation with the aluminum template) and the scalpel compared with laser incisions made without using a template. The use of metal or sapphire heat-conducting templates reduced the wound-healing delay of laser incisions seen at postoperative days 7 and 14.

Reduction in lateral thermal damage using heat-conducting templates: a comparison of continuous wave and pulsed CO2 lasers

BACKGROUND AND OBJECTIVES

The advantages of the continuous wave (c.w.) CO(2) laser are offset by the delay in laser wound healing secondary to thermal damage. We have developed novel heat-conducting templates to reduce laser thermal damage. Because shortened pulse durations also decrease thermal damage, we tested the effectiveness of heat-conducting templates with a c.w. CO(2) clinical laser and a short-pulsed CO(2) laser to determine the best method and mechanism to minimize thermal damage.

STUDY DESIGN/MATERIALS AND METHODS

Comparison of 0.2-second shuttered c.w. and 5-microsecond pulsed CO(2) lasers were made by doing incisions on 150 tissue samples from reduction mammoplasties and abdominoplasties. Copper, aluminum, glass, and Plexiglass heat-conducting templates were tested against no template (air) with both lasers. Histological samples were evaluated using computerized morphometrics analysis.

RESULTS

Statistically significant reductions in lateral thermal damage were seen with the copper (50%) and aluminum (39%) templates used with the c.w. CO(2) laser. Only the copper template (39%) significantly reduced thermal damage when used with the pulsed CO(2) laser. Less thermal damage was seen using the pulsed CO(2) laser compared to the c.w. CO(2) laser with each template.

CONCLUSIONS

Heat-conducting templates significantly reduced the amount of lateral thermal damage when used with the c.w. CO(2) laser (copper and aluminum) and short-pulsed CO(2) laser (copper). The c.w. CO(2) laser with the copper template compared favorably to the short-pulsed CO(2) laser without a template. Therefore, both heat conductive templates and short-pulse structure provide successful methods for reducing lateral thermal damage, and a combination of the two appears to provide optimal results.