Pulsed erbium laser ablation of hard dental tissue: the effects of atomized water spray versus water surface film

Abstract

It has been established that the ability of erbium lasers to ablate hard dental tissue is due primarily to the laserinitiated subsurface expansion ofthe interstitial water trapped within the enamel and that by maintaining a thin film of water on the surface of the tooth, the efficiency of the laser ablation is enhanced. It has recently been suggested that a more aggressive ablative mechanism, designated as a hydrokinetic effect, occurs when atomized water droplets, introduced between the erbium laser and the surface of the tooth, are accelerated in the laser's field and impact the tooth's surface. It is the objective ofthis study to determine ifthe proposed hydrokinetic effect exists and to establish its contribution to the dental hard tissue ablation process. Two commercially available dental laser systems were employed in the hard tissue ablation studies. One system employed a water irrigation system in which the water was applied directly to the tooth, forming a thin film of water on the tooth's surface. The other system employed pressurized air and water to create an atomized mist of water droplets between the laser hand piece and the tooth. The ablative properties of the two lasers were studied upon hard inorganic materials, which were void of any water content, as well as dental enamel, which contained interstitial water within its cystalline structure. In each case the erbium laser beam was moved across the surface of the target material at a constant velocity. When exposing material void of any water content, no ablation of the surfaces was observed with either laser system. In contrast, when the irrigated dental enamel was exposed to the laser radiation, a linear groove was formed in the enamel surface. The volume of ablated dental tissue associated with each irrigation method was measured and plotted as a function of the energy within the laser pulse. Both dental laser systems exhibited similar enamel ablation rates and comparable ablated surface characteristics. The results of the study suggest that, although the manner in which the water irrigation was introduced differed, the mechanism by which the enamel was removed appeared basically the same for both dental laser systems, namely rapid subsurface expansion of the interstitially trapped water. It is the conclusion of this study that if the proposed hydrokinetic effect exists, it is not effective on hard materials, which are void of water, and it does not contribute in any significant degree in the ablation of dental enamel.

The current status of laser applications in dentistry

“…67 Detailed studies of the cutting mechanisms of Er:YAG and Er,Cr:YSGG lasers have revealed that the mechanism by which enamel is removed is basically the same for both laser systems, namely explosive subsurface expansion of interstitially trapped water. 65 The same investigations also failed to show Er,Cr:YSGG laser cutting of a variety of materials which were free of water, which the authors stated was 'contradictory to the existence of the hydrokinetic phenomenon'. 65 An important theoretical extension to the principle of water-based laser ablation of tooth structure is the recently described effect of 'laser abrasion', in which Er:YAG laser energy is used to accelerate the movement of particles of sapphire 30-50 micrometers in diameter in aqueous suspension.…”

“…65 The same investigations also failed to show Er,Cr:YSGG laser cutting of a variety of materials which were free of water, which the authors stated was 'contradictory to the existence of the hydrokinetic phenomenon'. 65 An important theoretical extension to the principle of water-based laser ablation of tooth structure is the recently described effect of 'laser abrasion', in which Er:YAG laser energy is used to accelerate the movement of particles of sapphire 30-50 micrometers in diameter in aqueous suspension. As in air abrasion, the impact of these particles causes brittle splitting, resulting in tooth substance removal.…”

Surgical lasers and hard dental tissue

“…Investigation into this effect has questioned the validity of such claims and in addition, with comparable incident energies, suggested that the ablation rate of the erbium YSGG with enamel is slightly slower than that of erbium YAG. 34 As mentioned above, this might be explained by the absorption dynamics of the YSGG and transfer of conductive heat from …”

“…This laser is similar to the Er:YAG in that it is absorbed by water and both wavelengths ablate through vaporisation of interstitial water, 34 although the absorption coeffi cient is slightly lower (4,000 cm -1 vs 13,000 cm -1 for Er:YAG). When one examines the absorption curve of CHA (enamel), there is a peak, coincident with 2,700 nm, representing absorption by the hydroxyl group (OH -) contained in the mineral molecule ( Fig.…”

Erbium Laser-assisted Closed-flap Crown Lengthening: A Review of the Literature

“…A water coolant and short pulse duration minimizes the heat transfer to the tooth. [15][16][17] By adjusting the power density, the erbium lasers can be used to create similar microexplosions in soft tissue. This causes a "shaving" or "planing" of the soft tissue rather than the deeper absorbed action of dedicated soft-tissue lasers.…”