Application of synchrotron-radiation-based computer microtomography (SRμCT) to selected biominerals: embryonic snails, statoliths of medusae, and human teeth

Synchrotron X-ray Studies of the Structural and Functional Hierarchies in Mineralised Human Dental Enamel: A State-of-the-Art Review

Hard dental tissues possess a complex hierarchical structure that is particularly evident in enamel, the most mineralised substance in the human body. Its complex and interlinked organisation at the Ångstrom (crystal lattice), nano-, micro-, and macro-scales is the result of evolutionary optimisation for mechanical and functional performance: hardness and stiffness, fracture toughness, thermal, and chemical resistance. Understanding the physical-chemical-structural relationships at each scale requires the application of appropriately sensitive and resolving probes. Synchrotron X-ray techniques offer the possibility to progress significantly beyond the capabilities of conventional laboratory instruments, i.e., X-ray diffractometers, and electron and atomic force microscopes. The last few decades have witnessed the accumulation of results obtained from X-ray scattering (diffraction), spectroscopy (including polarisation analysis), and imaging (including ptychography and tomography). The current article presents a multi-disciplinary review of nearly 40 years of discoveries and advancements, primarily pertaining to the study of enamel and its demineralisation (caries), but also linked to the investigations of other mineralised tissues such as dentine, bone, etc. The modelling approaches informed by these observations are also overviewed. The strategic aim of the present review was to identify and evaluate prospective avenues for analysing dental tissues and developing treatments and prophylaxis for improved dental health.

Mineral in skeletal elements of the terrestrial crustacean Porcellio scaber: SRμCT of function related distribution and changes during the moult cycle

Terrestrial isopods moult first the posterior and then the anterior half of the body, allowing for storage and recycling of CaCO₃. We used synchrotron-radiation microtomography to estimate mineral content within skeletal segments in sequential moulting stages of Porcellio scaber. The results suggest that all examined cuticular segments contribute to storage and recycling, however, to varying extents. The mineral within the hepatopancreas after moult suggests an uptake of mineral from the ingested exuviae. The total maximum loss of mineral was 46% for the anterior and 43% for the posterior cuticle. The time course of resorption of mineral and mineralisation of the new cuticle suggests storage and recycling of mineral in the posterior and anterior cuticle. The mineral in the anterior pereiopods decreases by 25% only. P. scaber has long legs and can run fast; therefore, a less mineralised and thus lightweight cuticle in pereiopods likely serves to lower energy consumption during escape behaviour. Differential demineralisation occurs in the head cuticle, in which the cornea of the complex eyes remains completely mineralised. The partes incisivae of the mandibles are mineralised before the old cuticle is demineralised and shed. Probably, this enables the animal to ingest the old exuviae after each half moult.

Non-destructive evaluation of teeth restored with different composite resins using synchrotron based micro-imaging

BACKGROUND

Application of high resolution synchrotron micro-imaging in microdefects studies of restored dental samples.

OBJECTIVE

The purpose of this study was to identify and compare the defects in restorations done by two different resin systems on teeth samples using synchrotron based micro-imaging techniques namely Phase Contrast Imaging (PCI) and micro-computed tomography (MCT). With this aim acquired image quality was also compared with routinely used RVG (Radiovisiograph).

METHODS

Crowns of human teeth samples were fractured mechanically involving only enamel and dentin, without exposure of pulp chamber and were divided into two groups depending on the restorative composite materials used. Group A samples were restored using a submicron Hybrid composite material and Group B samples were restored using a Nano-Hybrid restorative composite material. Synchrotron based PCI and MCT was performed with the aim of visualization of tooth structure, composite resin and their interface.

RESULTS

The quantitative and qualitative comparison of phase contrast and absorption contrast images along with MCT on the restored teeth samples shows comparatively large number of voids in Group A samples.

CONCLUSIONS

Quality assessment of dental restorations using synchrotron based micro-imaging suggests Nano-Hybrid resin restorations (Group B) are better than Group A.

Advances in biological structure, function, and physiology using synchrotron X-ray imaging*

Studies of the physiology and biomechanics of small ( approximately 1 cm) organisms are often limited by the inability to see inside the animal during a behavior or process of interest and by a lack of three-dimensional morphology at the submillimeter scale. These constraints can be overcome by an imaging probe that has sensitivity to soft tissue, the ability to penetrate opaque surfaces, and high spatial and temporal resolution. Synchrotron X-ray imaging has been successfully used to visualize millimeter-centimeter-sized organisms with micrometer-range spatial resolutions in fixed and living specimens. Synchrotron imaging of small organisms has been the key to recent novel insights into structure and function, particularly in the area of respiratory physiology and function of insects. X-ray imaging has been effectively used to examine the morphology of tracheal systems, the mechanisms of tracheal and air sac compression in insects, and the function of both chewing and sucking mouthparts in insects. Synchrotron X-ray imaging provides an exciting new window into the internal workings of small animals, with future promise to contribute to a range of physiological and biomechanical questions in comparative biology.

Characterisation of enamel white spot lesions using X-ray micro-tomography

OBJECTIVES

The aim of this study was to characterise the mineral density (MD) of natural enamel white spot lesions (WSLs) using X-ray micro-tomography calibrated with different density hydroxyapatite phantoms.

METHODS

Seven natural WSLs from four extracted non-carious premolar teeth were scanned at a voxel size of 7.6 microm using a desktop X-ray micro-tomography system. Five hydroxyapatite phantoms (sintered pellets of hydroxyapatite powder) with densities ranging from 1.52 to 3.14 g/cm(3) were used as calibration standards for each scan. Three-dimensional image reconstruction enabled MD gradients throughout the lesion to be quantified using an MD calibration equation derived from hydroxyapatite phantoms. Background noise generated during the measurement of MD was reduced using a Gaussian filter.

RESULTS

Gaussian filter reduced the signal-to-noise ratio (standard deviation) significantly while the basic MD information (average value) remained intact. The mineral gradients through the WSLs examined were compared and are discussed in terms of existing literature. The MD of sound enamel, apparent intact surface layer of WSL, and lowest level of WSL was found to be 2.65-2.89 g/cm(3), 2.23-2.58 g/cm(3) and 1.48-2.03 g/cm(3), respectively. Our MD results are comparable with other studies.

CONCLUSIONS

X-ray micro-tomography is a sensitive in vitro technique capable of characterising and quantifying MD of small non-cavitated WSLs. This method has a promising potential for future carious and quantitative remineralisation studies.

Skeletal deformations in medaka (Oryzias latipes) visualized by synchrotron radiation micro-computer tomography (SRmicroCT)

Synchrotron radiation micro-computer tomography (SRmicroCT) offers the possibility to investigate biomineralized structures in high detail. Two animals of adult medaka fish (Oryzias latipes) were analyzed by SRmicroCT with a resolution of 6.55 microm: the wild-type animal was normally developed whereas the second animal showed an idiopathic deformation of the cranial and axial skeleton. These deformations could be followed on the macro- and on the microscale (i.e., on the level of the individual ribs and fin bones). Our study clearly demonstrates that SRmicroCT is an excellent technique to study alterations in the skeletal structure of fish in detail.