Abstract
OBJECTIVES: An atomic force microscope (AFM) was used to analyze the changes in organic matter in human dentin and the effects of laser irradiation with different energy densities on the surface micro-nanostructures of human dentin. METHODS: Extracted human third molars were used in this study. Human dentin were scanned with an Er, Cr:YSGG laser (6.18, 8.04, 9.89, 11.1 J·cm(-2)). The 12 samples were randomly allocated. AFM phase imaging technology and energy-dispersive spectroscopy (EDS) were applied to detect the proportional changes in the organic components on the dentine surface before and after Er,Cr:YSGG laser irradiation. AFM was capable of observing the morphological changes of the dentine surface and hydroxyapatite crystals before and after Er, Cr:YSGG laser irradiation. RESULTS: After laser irradiation, the proportion of collagen with low contrast in the phase images remarkably reduced. Accordingly, the proportion of the inorganic phase significantly increased. EDS results showed that dentine was composed of Ca, P, O, and C and some trace elements of Na, Mg and Cl. After Er, Cr:YSGG laser irradiation, the C, O, and Na contents and C/Ca ratio declined significantly (P<0.05), whereas the Ca and P contents and the Ca/P ratio obviously increased (P<0.05). CONCLUSIONS: Irradiating human dentine with an Er, Cr:YSGG laser at varying energy densities from 6.18 to 11.1 J·cm(-2) did not significantly influence the inorganic phase structure of the surface dentine layer. However, thermal ablation occurred in the organic component.