Ultrastructural Analysis of Irradiated Dentin with Preventive Purpose

OBJECTIVE: This study investigated the surface micromorphology of healthy dentine before and after Er,Cr:YSGG laser application when irradiated with preventive purposes, using atomic force microscopy (AFM). METHODS: Five discs of bovine dentin were irradiated using an Er,Cr:YSGG laser (λ=2.78µm), using a 750µm diameter sapphire tip, at energy density of 2.8J/cm² (12.5 mJ/pulse) and repetition rate of 20Hz. Before and after irradiation, surface topography was analyzed by AFM using a Si probe in tapping mode with a scan size of 80x80µm² in fixed resolution of 512x512 points at 1Hz. Quantitative and qualitative information concerning the power spectral density (PSD), roughness (Ra) and cross-section analysis were obtained from areas of the center and periphery of laser pulses and the non-irradiated regions of the same specimen. RESULTS: The dentinal roughness parameter (Ra) of center and periphery of laser pulses and of the non-irradiated regions was, respectively, 83.48(±6.34)nm, 45.8(±13.47)nm and 35.18(±2.9)nm. The central region of laser pulses presented nodules between 30-45nm height and 0.8-2.2µm width, the peripheral region presented nodules of 10-30nm height and 0.8-2.2µm width, and the non-irradiated region presented no nodules. The PSD analysis of dentin demonstrated a contribution in the wavelengths between 0.8-2.2µm of 2 times (p<0.05) compared to non-irradiated region and of 1.6 times (p<0.05) compared to pulse periphery region. The central region of laser pulses presented higher ablation of intertubular region, about 340-760nm height, while peripheral and non-irradiated regions presented no difference in height of inter-peritubular dentin. CONCLUSION: Even when used at sub-ablative parameter, Er,Cr:YSGG laser is able to promote a significant increase of dentin roughness, mainly at the pulse center, which is due to the ablation of intertubular region. Besides that, AFM technique is able to provide qualitative and quantitative information of the extension of the structural changes caused by laser irradiation on dentin. Supported by CAPES.