Dental restorations should match the color of the surrounding enamel. Carefully selecting the appropriate shade for the filling material is a challenge for dentists. Moreover, tooth color can change over time due to habits such as smoking or drinking coffee. In the last few years, single-shade dental composites have come to the market. They rely on a chameleon effect to provide acceptable to good color matching regardless of the tooth color. The chameleon effect refers to a dental filling’s ability to guide light in such a way that its color blends in with that of the tooth. Structural color is a contributing factor to the chameleon effect and an active area of research where structures at the submicron scale play a critical role. We investigated the size, shape, and three-dimensional spatial arrangement of filler particles in single-shade dental resin composites. Cylindrical samples of dental composites were prepared and imaged with the transmission X-ray microscope at the ANATOMIX beamline, Synchrotron SOLEIL, France. The centers of the filler particles were determined from the tomography data. Combined with shape information from scanning electron microscopy, a Monte Carlo approach was used to model the transmittance for light at wavelengths from the visible to the ultraviolet. The results were compared to optical transmission measurements. The combination of nanotomography and simulation can thus help to understand the influence of the size and distribution of filler particles on the chameleon effect.
Cementum deposits on mammalian teeth contain layered microstructures associated with the chronological age of an animal and other details of their life history. Hard X-ray tomography data captured this record contained within the cementum deposits from whole teeth without sectioning. We investigated three teeth of African bovids, namely gemsbok (Oryx gazella), eland (Taurotragus oryx), and African or Cape buffalo (Syncerus caffer) using the laboratorybased system nanotom m for measuring each complete tooth to identify relevant regions, which were scanned at the ANATOMIX beamline of Synchrotron SOLEIL, France. Using microtomography in archaeological materials such as teeth, eliminates the need for tooth sectioning, making it a desirable alternative for archaeologists and museum curators. Synchrotron measurements enabled the application of pixel sizes as low as 0.65µm, which generated around 40 TB of data. The three adult bovids investigated here, have a known day of death and season of death, and come from regions with distinct seasonal patterns in temperature and/or rainfall. They also have an estimated age at death based on occlusal wear. The known information serves as a control to determine the applicability of microtomography on whole teeth of large bovids. Preliminary results show that microtomography can successfully replace the need of sectioning in cementum dental analysis. Our future goal is to develop a protocol to standardize procedures of tooth cementum analysis in bovids using microtomography.
Comparable to annual rings present in a tree trunk, human tooth cementum contains yearly deposited incremental layers often termed incremental lines, which are generally visualized from tooth slides with optical microscopy in two dimensions. These micrometer-thin incremental lines are used to decode age-at-death and stress periods over the lifetime of an individuum. One can also visualize these layers without physical slicing by means of hard X rays because of density modulations. Within this project, two optically almost transparent tooth slides were used to record optical data in two dimensions with submicron pixel sizes. These data were registered with projections of available synchrotron radiation-based tomography data of the slides. Such data were also acquired for an entire tooth to determine thickness variations in each layer, the intra-layer thickness, and variations between the layers, the inter-layer thickness, automatically.
Nanotechnology-based dental composites, see Tokuyama Dental's OMNICHROMA, can address the issue of color mismatch between tooth and filling. Similar to a chameleon, the filling can match the color of the surrounding enamel. We thoroughly investigated the nanostructure of the composite and the related optical properties using electron microscopy, synchrotron radiation-based nanotomography, small-angle X-ray scattering and optical transmission measurements. The spherical silica-zirconia fillers show a size of 260 nm and form micrometer-sized spherical domains of close-packed nanospheres. The aim of the study is to quantify the chameleon effect and discuss possible paths towards biomimetic anisotropic dental composites with improved color matching.
Hard X-ray micro computed tomography can be used for three-dimensional histological phenotyping of zebrafish embryos down to 1 µm or below without the need for staining or physical slicing. Current advances in ze- brafish embryo imaging, however, mostly rely on synchrotron radiation sources or highly advanced laboratory sources, which despite their evident strengths with regard to their beam properties and the implementation of phase contrast imaging techniques, lack accessibility. Therefore, we evaluated the performance of a conventional SkyScan 1275 laboratory µCT scanner in absorption contrast mode for the visualization of anatomical features in ethanol- and paraffin-embedded zebrafish embryos. We compare our results to readily available synchrotron data where 35 anatomical structures were identified. Despite having a more than ten times larger voxel length, approximately two thirds of the features could also be determined with laboratory microtomography. This could allow to monitor morphological changes during development or disease progression on large sample numbers, enabling the performance of preclinical studies in a local laboratory.
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