Mechanism of water augmentation during IR laser ablation of dental enamel

Abstract

Background and Objectives: The mechanism of water augmentation during IR laser ablation of dental hard tissues is controversial and poorly understood. The influence of an optically thick applied water layer on the laser ablation of enamel was investigated at wavelengths in which water is a primary absorber and the magnitude of absorption varies markedly. Study Design/Materials and Methods: Q-switched and free running Er: YSGG (2.79 mm) and Er:YAG (2.94 mm), free running Ho:YAG and 9.6 mm TEA CO 2 laser systems were used to produce linear incisions in dental enamel with and without water. Synchrotron-radiation IR spectromicroscopy with the Advanced Light Source at Lawrence Berkeley National Laboratory was used to determine the chemical changes across the laser ablation profiles with a spatial resolution of 10-mm. Results: The addition of water increased the rate of ablation and produced a more desirable surface morphology during enamel ablation with all the erbium systems. Moreover, ablation was markedly more efficient for Q-switched (0.15 microsecond) versus free-running (150 microsecond) erbium laser pulses with the added water layer. Although the addition of a thick water layer reduced the rate of ablation during CO 2 laser ablation, the addition of the water removed undesirable deposits of non-apatite mineral phases from the crater surface. IR spectromicroscopy indicates that the chemical composition of the crater walls deviates markedly from that of hydroxyapatite after Er:YAG and CO 2 laser irradiation without added water. New mineral phases were resolved that have not been previously observed using conventional IR spectroscopy. There was extensive peripheral damage after irradiation with the Ho:YAG laser with and without added water without effective ablation of enamel. Conclusions: We postulate that condensed mineral phases from the plume are deposited along the crater walls after repetitive laser pulses and such non-apatitic phases interfere with subsequent laser pulses during IR laser irradiation reducing the rate and efficiency of ablation. The ablative recoil associated with the displacement and vaporization of the applied water layer removes such loosely adherent phases maintaining efficient ablation during multiple pulse irradiation.

CO₂ and Er,Cr:YSGG Laser Applications in Debonding Ceramic Materials: An in Vitro Study

“…Many studies also report the appearance of carbonized resin areas in the enamel/dentin and in the ceramic [12,13,14], compatible with the ones that we obtain and named discoloration variable, probably caused by not using irrigation during the irradiation. Mimura et al [15] describes it as MMA resin remaining on the tooth surface after debonding with CO 2.…”

Tensile Bond Strength of Er, Cr: YSGG Laser-irradiated Human Dentin to Composite Inlays with Two Resin Cements

“…After efficient absorption of laser energy, water droplets produce violent microexpansion and simultaneously cut dental hard tissues 21) . In comparison with high-speed bur preparation, cavities prepared with laser are relatively painless and produce less vibration and heat 22) .…”

Clinical Comparison of Bur- and Laser-prepared Minimally Invasive Occlusal Resin Composite Restorations: Two-year Follow-up

“…These lasers emit energy in the wavelength of 2.94 µm and 2.78 µm, respectively, which coincides with the absorption peak of water and is well absorbed by all biological tissues, including enamel and dentin. 5 Once light from the laser is absorbed, it is converted to heat. The overheated water vaporizes and causes microexplosions that carry away surrounding tooth fragments.…”