Er:YAG Laser Modification of Root Canal Dentine: Influence of Pulse Duration, Repetitive Irradiation and Water Spray

Abstract

The aim of this study was to determine the effects of varying parameters of Er:YAG laser irradiation with and without water spray cooling on root canal dentine in vitro. After horizontally removing tooth crowns from extracted human teeth, roots were axially sectioned into thin slices, exposing the root canal surface. An Er:YAG laser delivered 10-30 J/cm(2) into a 0.4-mm diameter laser spot on the root canal surface. Single pulses of different lengths (80-280 micro s) were applied with and without water spray cooling/irrigation, and sequences of three pulses at a repetition rate of 30 Hz were applied at selected pulse parameters. The irradiated samples were investigated using both confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). At most irradiation conditions, the root canal dentine surface was ablated. Three-dimensional images from CLSM revealed that the cavity walls were not smooth. Depths of the cavities revealed significant differences between the cavities. No debris was observed at the surface of cavities at any irradiation condition. Strong melting and recrystallisation, or unusually flat surfaces with open dentinal tubules were obtained with sequences of three pulses without water cooling. CLSM is an effective tool for investigation of laser effects on root canal dentine. By varying the irradiation conditions, the Er:YAG laser can induce different modifications of root canal surface, which may be very interesting for root canal preparation.

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.…”

“…The reason for the different results could be caused by the thermal effect arising from 10 consecutive laser pulse irradiations without water spray cooling. Ebihara et al 20) reported that an Er: YAG laser with 80-μs pulse duration featured a deeper ablation effect than 180 and 280 μs at 20 J/cm 2 . The main purpose of their study 20) was to determine the surface and subsurface modifications of root canal dentin after Er: YAG laser irradiation under variable conditions.…”

“…Ebihara et al 20) reported that an Er: YAG laser with 80-μs pulse duration featured a deeper ablation effect than 180 and 280 μs at 20 J/cm 2 . The main purpose of their study 20) was to determine the surface and subsurface modifications of root canal dentin after Er: YAG laser irradiation under variable conditions. In their study 20) , energy densities in the range of 12-37 J/cm 2 were employed, which were lower than that recommended for efficient 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 .…”

“…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 . This was much lower than the fluence usually employed for cavity preparations with Er: YAG laser in the dental clinic.…”