Q-switched Nd:YAG laser on dental enamel with photoabsorber

Abstract

Nd:YAG lasers emitting λ = 1064 nm at microsecond and nanosecond pulses are alternatives to prevent dental caries and erosion in clinics. This wavelength allows most of photons to penetrate deep in the hard tissue due to low absorption of hydroxyapatite in the region. It is necessary to use photoabsorbers so most of photons are absorbed in the surface of the tissue preventing dental pulp necrosis. Currently the coal paste is used as a photoabsorber but the irradiated tissue turns darker what implies in the patients low adherence to the treatment due to aesthetic reasons. [1,2]. Confocal Raman spectroscopy is a non-destructive optical method to obtain detailed information about molecular composition of biological structures in depth. The most prominent feature of Confocal Raman spectroscopy is the reliable capability to provide the biomolecular data with no use of ionizing radiation to penetrate in the sample. This work aims to characterize the dental enamel irradiated with Nd:YAG laser with nanoseconds pulses, in order to describe the depth related changes promoted in the enamel, by the heat generated due to laser irradiation. For these measurements, 30 bovine enamel blocks of 8 mm2, were randomized into 3 groups: G1 – enamel untreated; G2 – enamel irradiated with Nd:YAG nanopulsed laser (1064 nm, 4 W; 1,05 J/cm2; 5 ns 20 Hz, Brilliant, Quantel Laser) using a coal paste as photoabsorber; G3 -enamel irradiated with Nd:YAG nanopulsed laser ( same parameters as G2) using squid ink as photoabsorber. The assessments of three different depth regions of the cubic shaped samples were: region A- left corner above of the sample, region B-middle of the sample and Region C- right corner below of the sample. The intensity map of phosphate (950 cm-1) regarding the position, were calculated [3,4] as shown in the Figure 01. The comparative results in the Fig.1 demonstrated that application of coal paste associated with Nd:YAG (G2) can preserve the inorganic content better than the squid ink group (G3). These findings have crucial clinical implications in the laser protocol development and it was possible to correlate the heat penetration depth of the laser irradiation with photoabsorber using the images obtained by the confocal Raman.