Influence of tissue desiccation on critical temperature for thermal damage during Er:YAG laser skin treatments.

OBJECTIVES

Erbium lasers have become an accepted tool for performing both ablative and non-ablative medical procedures, especially when minimal invasiveness is desired. Hard-tissue desiccation during Er:YAG laser procedures is a well-known phenomenon in dentistry, the effect of which is to a certain degree being addressed by the accompanying cooling water spray. The desiccation of soft tissue has attracted much less attention due to the soft tissue's high-water content, resulting in a smaller effect on the ablation process.

MATERIALS AND METHODS

In this study, the characteristics of skin temperature decay following irradiations with Er:YAG laser pulses were measured using a fast thermal camera.

RESULTS

The measurements revealed a substantial increase in temperature decay times and resulting thermal exposure times following irradiations with Er:YAG pulses with fluences below the laser ablation threshold. Based on an analytical model where the skin surface cooling time is calculated from the estimated thickness of the heated superficial layer of the stratum corneum (SC), the observed phenomena is attributed to the accelerated evaporation of water from the SC's surface. By using an Arrhenius damage integral-based variable heat shock model to describe the dependence of the critical temperature on the duration of thermal exposure, it is shown that contrary to what an inexperienced practitioner might expect, the low-to-medium level fluences may result in a larger thermal damage in comparison to treatments where higher fluences are used. This effect may be alleviated by hydrating the skin before Er:YAG treatments.

CONCLUSION

Our study indicates that tissue desiccation may play a more important role than expected for soft-tissue procedures. It is proposed that its effect may be alleviated by hydrating the skin before Er:YAG treatments.