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Dentin hypersensitivity is an oral health concern affecting a large percentage of the world's adult population. Occlusion of the exposed dentinal tubules is among the treatment options available, and silver diammine fluoride (SDF) is an occluding agent used for interrupting or dampening the stimulus of the dental pulp nerves that produce pain. In addition to dentin permeability testing, the evaluation of desensitizing agents occluding dentinal tubules strongly relies on microscopic techniques, such as scanning electron microscopy (SEM). Limitations of SEM are that it provides only surface images that lack detailed information on the depth of penetration and amount of material present within the treated specimen, and it is prone to sample preparation artifacts. Here, we present high-resolution X-ray computed tomography (nano-CT) as a potential method for investigating dentin specimens with occluded tubules. We studied human dentin treated with SDF as an exemplary dentinal occlusion treatment option. We evaluated the silver deposits formed on the dentin surface region near the dentinal tubules and in the tubular regions using cross-section SEM, Energy Dispersive X-ray (EDX) analysis, and nano-CT. The resulting images obtained by SEM and nano-CT had comparable resolutions, and both techniques produced images of the tubules' occlusion. Nano-CT provided three-dimensional images adequate to quantitate tubule size and orientation in space. Moreover, it enabled clear visualization of dentinal tubules in any virtual plane and estimation of the amount and depth of occluding material. Thus, nano-CT has the potential to be a valuable technique for evaluating the occluding effects of virtually any material applied to dentinal tubules, supporting deciding between the best occluding treatment options. [ABSTRACT FROM AUTHOR]

• XCT and 3D-image analysis of glass sphere compacts during sintering. • Coarseness C is used to parameterise local relative density distributions. • Decrease in C between initial and final sintering stages. • Intermediate stage with highest C and bimodal distribution of closed and interconnected pores. • Spatial heterogeneity of local particle/pore arrangements is biased by substrate effects. Using high-resolution X-ray computed tomography and 3D image analysis, the global relative density was determined and fluctuations in relative density were localized and quantified in a series of sintered glass bodies made of 80 μm glass spheres over the entire sintering process. A representative volume element (RVE) in the sintered body was divided into cubic volumes of 500, 250 and 125 µm edge length by an automatic segmentation routine. It was found that the expected decrease in coarseness C from the initial to the final sintering stage is interrupted by an intermediate stage with highest C and a characteristic bimodal density distribution. The bimodality of the intermediate stage is due to spatially separated denser arrangements within the RVE with closed pores and less dense arrangements with a network of interconnected or open pores. The spatial heterogeneity is biased in the z-direction due to friction caused by adhesion with the substrate. [ABSTRACT FROM AUTHOR]

• The microstructure characterization of a glass-sintered compact is presented based on local density fluctuation. • Local density fluctuation is assessed based on 3D data as a function of observation region. • The degree of heterogeneity of the microstructure is calculated by the coarseness parameter. • Local density fluctuation is represented by a normal probability distribution function. • The coarseness parameter is dependent on the observation region. The relative density of a sintered glass-powder compact varies at the local level due to its heterogeneous nature, which makes its characterization essential. In this work, high-resolution X-ray computed tomography (XCT) was used to quantitatively characterize the local relative density fluctuation of a sintered glass compact in its initial stage. The degree of heterogeneity of the microstructure was calculated taking into account the coarseness parameter. With a basis of 23,500 particles scanned in the representative volume element (RVE), the local environment was subdivided into three different groups of particles, represented by a cubic cell with a volume equivalent to that of approximately 600, 80 and 10 spherical particles with a diameter of 80 μm. Independent of the particle group analysed, we found that the maximum of the local relative density distributions, which could be described by a normal distribution function, always occurs around the relative density of the RVE. However, the fluctuation of the data showed a considerable change regarding the width, which increases as the volume of the analysed group of particles decreases, suggesting that particle packing is more heterogeneous on a small scale. In particular, we observed that the heterogeneity of the microstructure for the RVE under consideration becomes pronounced for groups of approximately 10 to 80 particles. Image, graphical abstract [ABSTRACT FROM AUTHOR]