Atomic force microscopy observation of the effect of laser ablation on the nanostructures of the dentin surface.

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.

[Case-control study on risk factors of recurrent aphthous ulcer].

PURPOSE: To evaluate the risk factors for the occurrence of recurrent aphthous ulcer (RAU) in Fuzhou city by case-control study. METHODS: A questionnaire survey of 113 patients with RAU and 102 non-RAU patients in the same hospital was made, including 58 items. Chi-square test and conditional logistic regression were used for monovariate and multivariate analysis respectively with SPSS23.0 software package. RESULTS: One-way Chi-square test showed that immigrants, genetic factors, gastrointestinal disorders, menstrual period, oral health status, anxiety were related factors for patients suffering from RAU. Conditional logistic regression analysis indicated that genetic factors as well as more dental calculus in the oral cavity were RAU risk factors. Tendency Chi-square test revealed that there was a negative correlation between the occurrence of RAU and vegetable intake, and a positive correlation with the amount of dental calculus and soft scale in the oral cavity. CONCLUSIONS: The occurrence of RAU is the result of combination of "multiple factors" in the digestive system, genetic system, immune system and oral microenvironment.