Abstract
Human dentine is a hierarchical mineralized tissue with a two-level composite structure, with tubules being the prominent structural feature at a microlevel, and collagen fibres decorated with hydroxyapatite (HAp) crystallite platelets dominating the nanoscale. Few studies have focused on this two-level structure of human dentine, where the response to mechanical loading is thought to be affected not only by the tubule volume fraction at the microscale, but also by the shape and orientation distribution of mineral crystallites, and their nanoscale spatial arrangement and alignment. In this paper, in situ elastic strain evolution within HAp in dentine subjected to uniaxial compressive loading along both longitudinal and transverse directions was characterized simultaneously by two synchrotron X-ray scattering techniques: small- and wide-angle X-ray scattering (SAXS and WAXS, respectively). WAXS allows the evaluation of the apparent modulus linking the external load to the internal HAp crystallite strain, while the nanoscale HAp distribution and arrangement can be quantified by SAXS. We proposed an improved multiscale Eshelby inclusion model that takes into account the two-level hierarchical structure, and validated it with a multidirectional experimental strain evaluation. The agreement between the simulation and measurement indicates that the multiscale hierarchical model developed here accurately reflects the structural arrangement and mechanical response of human dentine. This study benefits the comprehensive understanding of the mechanical behaviour of hierarchical biomaterials. The knowledge of the mechanical properties related to the hierarchical structure is essential for the understanding and predicting the effects of structural alterations that may occur due to disease or treatment on the performance of dental tissues and their artificial replacements.
Highlights
Dentine is a hydrated biological mineral composite tissue with a hierarchical structure and versatile mechanical properties [1]
Dentine is a composite of platelike hydroxyapatite crystals (HAp) that have the shape of elongated pancakes ($2–4 nm thick, $30 nm wide and up to 100 nm long) randomly embedded in a collagen matrix [4,5]
The apparent radial shifts of the (0 0 2) peak in the WAXS pattern were measured under uniaxial compressive loading applied on both longitudinal and transverse directions with respect to the preferential tubule direction
Summary
Dentine is a hydrated biological mineral composite tissue with a hierarchical structure and versatile mechanical properties [1]. Dentine is a composite of platelike hydroxyapatite crystals (HAp) that have the shape of elongated pancakes ($2–4 nm thick, $30 nm wide and up to 100 nm long) randomly embedded in a collagen matrix [4,5]. Few studies have focused on the nanoscale, where mechanical alterations can be considered to be a function of crystal shape and orientation of the mineral phase [7,8]. It is required to use techniques that allow in situ quantification of the mechanical response of nanoscale HAp phases to loading
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