Confocal Raman spectroscopy characterization of Nd:YAG laser irradiation on dental enamel for erosion prevention

Abstract

Confocal Raman spectroscopy is a non-destructive and non-invasive method used to obtain spectral features of biological structure and depth images without coming into contact with the sample. Biochemical content obtained by Raman microscopy is related to the characteristics of the tissues, allowing experimental use without any side effects to the sample. Complex biomolecular features can be resolved through confocal Raman imaging analysis with subcellular spatial resolution by using a single excitation wavelength laser to identify a large range of biomolecules. This work aims to characterize dental enamel irradiated by Nd:YAG laser and correlate the modified tissue in depth due to the heat propagation caused by laser absorption. For this, 30 blocks of bovine enamel were randomized into 3 groups: G1- enamel untreated; G2- enamel irradiated with Nd:YAG laser (1064 nm; 120s pulsewidth, 10Hz; 84,9 mJ/cm2; Lares Research) using a squid Ink as photoabsorber; G3- enamel irradiated with Nd:YAG laser (1064 nm; 5 ns; 20 Hz; 1,05 J/cm2 Brilliant, Quantel Laser) using a coal paste as photoabsorber. The phosphate intensity band was used as a spectral indicator of the groups characteristics. The Raman spectra of the Nd:YAG irradiated samples detected a phosphate intensity reduction in the G3 group after laser irradiation. There were distinct differences in the chemical activity after the laser irradiation and these findings, associated with the previous studies of our group, were related to the stability of the apatite, accompanied with the increased susceptibility to demineralization. The carbonate free apatite has been characterized as less likely to be affected by acid challenge. Based on our initial results, the thickness of the treated area is a critical variable in determining the resistance of erosion, especially for the type of photoabsorber associated with Nd:YAG. Our findings demonstrate the coal paste as a more resistant material to enamel erosion prevention. Therefore, fiber-optic confocal Raman imaging have shown potential to be an established spectroscopic choice for carie real-time monitoring.