The Ablation Threshold of Er:YAG and Er:YSGG Laser Radiation in Dental Enamel

Abstract

The scientific investigation of fundamental problems plays a decisive role in understanding the mode of action and the consequences of the use of lasers on biological material. One of these fundamental aspects is the investigation of the ablation threshold of various laser wavelengths in dental enamel. Knowledge of the relationships and influencing factors in the laser ablation of hard tooth tissue constitutes the basis for use in patients and the introduction of new indications. The present paper examines the ablation threshold of an Er:YAG laser (lambda=2.94 micro m) and an Er:YSGG laser (lambda=2.79 micro m) in human dental enamel. To this end, 130 enamel samples were taken from wisdom teeth and treated with increasing energy densities of 2-40 J/cm(2). The sample material was mounted and irradiated on an automated linear micropositioner. Treatment was performed with a pulse duration of tau(P(FWHM)) approximately 150 micro s and a pulse repetition rate of 5 Hz for both wavelengths. The repetition rate of the laser and the feed rate of the micropositioner resulted in overlapping of the single pulses. The surface changes were assessed by means of reflected light and scanning electron microscopy. On the basis of the results, it was possible to identify an energy density range as the ablation threshold for both the Er:YAG and the Er:YSGG laser. With the Er:YAG laser, the transition was found in an energy density range of 9-11 J/cm(2). The range for the Er:YSGG laser was slightly higher at 10-14 J/cm(2).

Impact of Er:YAG laser pulse duration on ultra-structure of dentin collagen fibrils

“…The Er:YAG laser has a wavelength (2.94 μm) which is absorbed by water (3.0 μm) and OH groups of hydroxyapatite (2.8 μm) [8,9], producing heating and water evaporation, which reach a high steam pressure resulting in successive micro-explosions and ejection of organic and inorganic particles [10].…”

The role of mesoscopic modelling in understanding the response of dental enamel to mid-infrared radiation

“…This is because the CO 2 laser causes all water pores at a given distance from the surface of the tooth to reach the temperature necessary to induce ablation simultaneously, irrespective of their size, whereas this is not so for the Er:YAG laser. The ablation threshold of enamel by free-running Er:YAG laser (with its characteristic macropulse composed of short micropulses of duration 0.5-5 µs) has indeed been shown to vary greatly between 2.5 and 20 J cm −2 (Apel et al 2002a). Unfortunately, equivalent experiments for the CO 2 laser have not been reported.…”

Surgical lasers and hard dental tissue

“…36 Apel et al further confi rmed this slight difference in their investigation into the ablation threshold of enamel with these lasers, fi nding values of 9-11 J cm -2 for Er:YAG and 10-14 J cm -2 for Er,Cr:YSGG. 37 Nonetheless, both laser wavelengths allow cavity preparation within acceptable clinical parameters. 38 Early erbium lasers had rudimentary handpieces which were comparatively heavy.…”