Dr Tayyaba Rabnawaz

[Display omitted] •3D SAXS tensor tomography (SASTT) reveals the 3D dentine nanostructure at high spatial resolution.•Carious lesions cause anisotropic disruption of mineralised collagen fibrils and hydroxyapatite crystallites (HAp) alignment.•Artificial demineralisation induces uniform mineral loss , initially preserving the collagen but compromising mechanical integrity.•Findings advance understanding of dental tissue mechanics and challenges associated with effective remineralisation. Dental caries, one of the most prevalent non-communicable diseases worldwide, is characterised by the progressive deterioration of the structure and mechanical properties of dental hard tissues. In human teeth, dentine is the most abundant mineralised tissue, forming the primary support material. To assess changes in the mechanical properties of dentine caused by dental caries and acid erosion, it is crucial to understand the relationship between organic and inorganic dentine components and their organisation into a 3D anisotropic structure at the nanoscale. Over the past 20 years, alterations in dentine structure caused by caries and artificial demineralisation have been reported using conventional microscopy techniques. However, due to the limited spatial resolution of these techniques, the 3D structural organisation including orientation and degree of alignment of mineralised collagen fibrils at the nanoscale, has not been fully explored. This study investigated alterations in the 3D structure of normal, carious and artificially demineralised dentine using SAXS tensor tomography (SASTT). This technique enabled the observation of differences in the local orientation of organic and inorganic components, as well as variations in local scattering intensity, resulting from natural caries and artificial demineralisation. In comparison to normal dentine, caries caused minor orientational differences of both components but had a major impact on the local X-ray scattering intensity. After artificial demineralisation of the dentine, most of the mineral was lost in the outer layers, resulting in a greater reduction in scattering intensity than that caused by caries. The remarkable mechanical properties of human dentine arise from its complex hierarchical 3D structure. In this article, we have investigated the 3D structural alterations in dentine, caused by caries and artificial demineralisation. For this detailed investigation, SAXS tensor tomography (SASTT) has been implemented on the I22 beamline at Diamond Light Source, UK. SASTT is a technique that can probe the nanostructure of dentine, yielding orientation and degree of alignment of the mineralised collagen fibrils, while also providing a 3D reciprocal space map to investigate the detailed non-uniform scattering intensity distribution in all directions. The initial SASTT data provide insights into dentine structural alterations caused by caries and artificial demineralisation, facilitating further exploration of structure–mechanical property relationships, which may lead to improve the development of novel biomimetic materials for dental applications.

Objectives Biomimetic hydroxyapatite (HAp)-based composites are promising materials for dental restorations due to their hierarchical structure and similarity to natural dental tissues. This study aims to investigate the three-dimensional crystallographic organization of HAp within nacre-inspired composites and to evaluate how different polymers infiltrations influence the structural orientation. Methods Nacre-inspired HAp ceramic scaffolds were fabricated via bidirectional freeze-casting and subsequently infiltrated with different polymers, including Polyurethane (PU), Poly(methyl methacrylate) (PMMA), Epoxy, and Urethane dimethacrylate (UDMA). The three-dimensional structural organization and crystallite orientation of these composites were investigated using synchrotron-based 3D SAXS tensor tomography (3D SASTT), complemented by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Results The results reveal distinct differences in crystallite alignment among the composites. HAp/PU exhibits the highest degree of preferred orientation (∼0.7–0.8), whereas HAp/PMMA and HAp/Epoxy show lower alignment values (∼0.2–0.4). The HAp/UDMA composite displays heterogeneous orientation with localized regions of moderate alignment. SEM and EDX analyses confirm variations in lamellar morphology, polymer infiltration, and porosity distribution across the composites. Significance These findings demonstrate that 3D SASTT enables quantitative mapping of nanoscale crystallite orientation within bulk biomimetic scaffolds and provides new insights into the hierarchical structure of composites, supporting structural design of advanced dental restorative materials.