<title>Threshold and efficiency analysis in Er:YAG laser ablation of hard dental tissue</title>

Abstract

Influence of pulselength on mid-infrared laser ablation of hard dental tissue was studied experimentally by applying free-generated Er:YAG laser pulses with pulselengths from 50 ts to 1 ms and different energies to dentin slices in vitro with no spray cooling. The results show that for pulselengths between 50 and 300 ps, dentin ablation turns up abruptly at a well defined fluence value ofapproximately 4 J/cm2, which is independent of the pulselength. Similarly, volumes of the resulting craters as a function of laser fluence at these pulselengths follow nearly the same curve, which corresponds well to a model of laser beam screening by the ejected debris. However, with 1 ms long laser pulses, the ablation turns up at laser fluences above 4 J/cm2 only gradually, reaching differential ablation efficiency similar as in previous cases at fluence values several times higher than the ablation threshold value. An estimate of this "second threshold" fluence and the pulselengths at which it should in general be observed are derived from a simple model of heat diffusion and ablation front dynamics.

Effect of Pulse Duration of Er: YAG Laser on Dentin Ablation

“…To date, few researchers have examined the effects arising from varied pulse durations of Er: YAG laser [20][21][22][23] . With varied laser pulse durations and energy fluences of Er: YAG laser, Majaron et al 21) quantitatively examined their effects on depth and diameter and calculated the crater volumes thereof.…”

“…With varied laser pulse durations and energy fluences of Er: YAG laser, Majaron et al 21) quantitatively examined their effects on depth and diameter and calculated the crater volumes thereof. The authors chiefly focused on energy density and did not discuss pulse duration in detail.…”

“…This was much lower than the fluence usually employed for cavity preparations with Er: YAG laser in the dental clinic. Similarly, Majaron et al 21) examined the influence of energy density with several pulse durations on the efficiency of dentin ablation. Different effects for different pulse durations were observed at different energy fluences.…”

“…Different effects for different pulse durations were observed at different energy fluences. It is also noteworthy that although the investigation 21) was carried out using a wide range of energy fluences, precise evaluation with an appropriate energy fluence for dentin ablation was not performed. Indeed, the present study was the first attempt that investigated the effect of pulse duration in detail with a suitable energy fluence for dentin ablation.…”

“…The pulse duration of most Er: YAG lasers on the market is fixed from 150 to 250 μsec, and the majority of published experiments have been performed with fixed pulse durations in that range [13][14][15][16][17]19) . Few researchers have examined the influence of varied pulse durations on dentin ablation with Er: YAG laser 20,21) . Ebihara et al 20) evaluated the depth of irradiated cavities of root canal dentin and reported that shorter pulse durations featured a deeper ablation effect at about 20 J/cm 2 .…”