Selectivity, efficiency, and surface characteristics of hard dental tissues ablated with ArF pulsed excimer lasers

Abstract

Lasers are finding expanding applications in the field of dentistry. Cutting in soft tissue, hard dental material ablation, caries removal, and root canal therapy are only a few examples of dental laser uses. In this article, the application of short pulse ArF excimer laser to ablation of dentin and enamel is investigated. In particular, the effect of laser pulse repetition rates (PRR) and fluence levels on the efficiency of the ablation process and on the average thermal response of ablated surfaces is investigated. Ablation of dentin was found to be considerably more efficient than the ablation of enamel and depends exponentially on the laser fluence. Both dentin and enamel surfaces showed an increase in surface temperature with repetition rate. At lower PRR, however, temperature increases are very small. Surface temperature was also found to increase with laser fluence, although this increase is very small at laser PRR of 5 Hz or less. Tissue ablation rates were found to be comparable to or better than other nanosecond lasers, and left smooth surfaces, free of thermal damage. Microscopic examination of the ablated surface shows no crack formation, charring, discoloration, or any other thermal damage. The ablated surfaces appear to be very smooth, highly polished, and glossy looking as if they were subjected to thermal melting. This observation is indeed confirmed under scanning electron microscopy (SEM), where evidence of localized melting of the tissue is observed. Furthermore, a close SEM examination of the dentin surface reveals a selectively ablated intertubular dentin, while the remaining pillar-like dentin tubules are sealed off with fused peritubular dentin. At all fluence levels and PRR, the first three to four pulses impinging on an untreated enamel surface produced unusually large plumes of debris which were different in size, texture, and fluorescence emission characteristics from the ablation products of subsequent pulses. It is believed that these different ablation characteristics are a consequence of the pulsed ArF laser's ability to selectively remove residual matter from the more resistant enamel surface.

Scanning electron microscopy of otic capsule and calvarial bone ablated by a holmium-YAG laser

“…Indeed. in earlier studies on the effects of excimer lasers on dentine we observed selective surface ablation of intertubular dentine, peritubular dentine or simply uniform 'coating of the crater bottom by a melted layer of hydroxyapatite' (34,35).…”

<title>Effects of XeCl excimer lasers and fluoride application on artificial caries-like lesions</title>

“…(10,12,13) documenting reduced roughness possibly associated with thermal effects at higher irradiation frequencies.…”

“…Several authors have investigated use of excimer lasers for ablation of enamel (10)(11)(12)(13)(14) . However, little is known about the susceptibility to caries of enamel after exposure to excimer laser irradiation.…”

Kagome fiber based ultrafast laser microsurgery probe delivering micro-Joule pulse energies

“…To apply this model to our objective's transmission measurements, we can approximate the 2-lens objective to a single representative, stationary ZnS crystal and set z to zero in Eq. (8). We can then represent the normalized transmission in terms of input peak power (P in ).…”

“…These ablation characteristics allow for extremely precise tissue removal with minimal damage to the surrounding tissue. Substantial research efforts over the last two decades have explored tissue ablation in the corneal stroma [3][4][5], cortical parenchyma [6], and epidermis [7], and harder tissue like nail [8] and dentin [9][10][11]. These studies led to the first clinical use of ultrafast lasers in laser assisted in situ keratomileusis (LASIK) for flap creation [3] and more recently for cataract surgery [12].…”