Multi-scale modeling and diffraction-based characterization of elastic behaviour of human enamel

The relationship between the ultrastructure of human enamel and its mechanical behaviour is studied in this paper. Two synchrotron X-ray diffraction techniques, wide and small angle X-ray scattering (WAXS/SAXS) were used in combination to obtain multi-scale quantitative information about the response of human enamel to in situ uniaxial compressive loading. The interpretation of WAXS data gives elastic lattice strains within the hydroxyapatite (HAp) crystals, the stiff reinforcing phase in human enamel. The apparent modulus was determined linking the external load and the internal HAp strain. SAXS interpretation, allows the quantification of the nano-scale HAp crystallite distribution within human enamel. A multi-scale Eshelby equivalent inclusion model of the enamel was proposed that represents the hierarchical mineralized tissue as a two-level composite: micro-level model with rod embedded in the homogenised enamel material, and nano-level model with HAp crystallites embedded in the rod. Satisfactory agreement was achieved between model and experiment, suggesting that the new multi-scale approach accurately reflects the structure and mechanics of human enamel, and may help guide new biomimetic designs

Multi-scale modeling and diffraction-based characterization of elastic behaviour of human enamel

The relationship between the ultrastructure of human enamel and its mechanical behaviour is studied in this paper. Two synchrotron X-ray diffraction techniques, wide and small angle X-ray scattering (WAXS/SAXS) were used in combination to obtain multi-scale quantitative information about the response of human enamel to in situ uniaxial compressive loading. The interpretation of WAXS data gives elastic lattice strains within the hydroxyapatite (HAp) crystals, the stiff reinforcing phase in human enamel. The apparent modulus was determined linking the external load and the internal HAp strain. SAXS interpretation, allows the quantification of the nano-scale HAp crystallite distribution within human enamel. A multi-scale Eshelby equivalent inclusion model of the enamel was proposed that represents the hierarchical mineralized tissue as a two-level composite: micro-level model with rod embedded in the homogenised enamel material, and nano-level model with HAp crystallites embedded in the rod. Satisfactory agreement was achieved between model and experiment, suggesting that the new multi-scale approach accurately reflects the structure and mechanics of human enamel, and may help guide new biomimetic designs

Structure-mechanical function relations at nano-scale in heat-affected human dental tissue.

The knowledge of the mechanical properties of dental materials related to their hierarchical structure is essential for understanding and predicting the effect of microstructural alterations on the performance of dental tissues in the context of forensic and archaeological investigation as well as laser irradiation treatment of caries. So far, few studies have focused on the nano-scale structure-mechanical function relations of human teeth altered by chemical or thermal treatment. The response of dental tissues to thermal treatment is thought to be strongly affected by the mineral crystallite size, their spatial arrangement and preferred orientation. In this study, synchrotron-based small and wide angle X-ray scattering (SAXS/WAXS) techniques were used to investigate the micro-structural alterations (mean crystalline thickness, crystal perfection and degree of alignment) of heat-affected dentine and enamel in human dental teeth. Additionally, nanoindentation mapping was applied to detect the spatial and temperature-dependent nano-mechanical properties variation. The SAXS/WAXS results revealed that the mean crystalline thickness distribution in dentine was more uniform compared with that in enamel. Although in general the mean crystalline thickness increased both in dentine and enamel as the temperature increased, the local structural variations gradually reduced. Meanwhile, the hardness and reduced modulus in enamel decreased as the temperature increased, while for dentine, the tendency reversed at high temperature. The analysis of the correlation between the ultrastructure and mechanical properties coupled with the effect of temperature demonstrates the effect of mean thickness and orientation on the local variation of mechanical property. This structural-mechanical property alteration is likely to be due to changes of HAp crystallites, thus dentine and enamel exhibit different responses at different temperatures. Our results enable an improved understanding of the mechanical properties correlation in hierarchical biological materials, and human dental tissue in particular

Structure-property characterization of the dentine-enamel junction (DEJ)

The dentine-enamel junction (DEJ) is an Important internal interface with strong and durable bonding between the hard outer layer (enamel) and the soft inner tooth core (dentine). This study investigated the microstructure of the DEJ by X-ray imaging method and synchrotron X-ray scattering techniques. Further high resolution elastic modulus mapping indicates that the DEJ is a band with a graded mechanical property rather than a discrete interface. The microstructure-property relationship is also illustrated. The knowledge of the architecture and properties of the natural DEJ will help in the biomimetic development of dental restorations and novel replacement materials and application techniques

Ultrastructural changes in burnt dental tissue revealed by synchrotron x-ray scattering

The investigation of ultrastructural alterations of skeletal hard tissue exposed to thermal treatment has been proven to be crucial to obtain a reliable estimation of thermal exposure for forensic and archaeological study. However, there is only limited data on the heat-induced compositional and structural alterations of dental tissue. Visualizing and understanding the internal architecture of these materials is a challenging task that cannot be readily accomplished by conventional microscopy methods alone. We describe some experimental arrangements making use of synchrotron X-ray beams that shed light on the ultrastructure alterations of dental tissue. In particular, SAXS was used to investigate the alterations in thermally treated dental tissues, aiming at probing the ultrastructural changes of hydroxyapatite (HAp). The information about the internal architecture (the variation of crystalline size and the orientation of HAp nano-particles) of dental tissues was collected, providing a basis for estimating the maximum temperature exposure of forensic dentine samples

X-ray scattering evaluation of ultrastructural changes in human dental tissues with thermal treatment

Micro- and ultrastructural analysis of burned skeletal remains is crucial for obtaining a reliable estimation of cremation temperature. Earlier studies mainly focused on heat-induced changes in bone tissue, while this study extends this research to human dental tissues using a novel quantitative analytical approach. Twelve tooth sections were burned at 400-900°C (30-min exposure, increments of 100°C). Subsequent combined small- and wide-angle X-ray scattering (SAXS/WAXS) experiments were performed at the Diamond Light Source synchrotron facility, where 28 scattering patterns were collected within each tooth section. In comparison with the control sample, an increase in mean crystal thickness was found in burned dentine (2.8-fold) and enamel (1.4-fold), however at a smaller rate than reported earlier for bone tissue (5-10.7-fold). The results provide a structural reference for traditional X-ray scattering methods and emphasize the need to investigate bone and dental tissues separately to obtain a reliable estimation of cremation temperature. © 2014 American Academy of Forensic Sciences

In situ X-ray scattering evaluation of heat-induced ultrastructural changes in dental tissues and synthetic hydroxyapatite.

Human dental tissues consist of inorganic constituents (mainly crystallites of hydroxyapatite, HAp) and organic matrix. In addition, synthetic HAp powders are frequently used in medical and chemical applications. Insights into the ultrastructural alterations of skeletal hard tissues exposed to thermal treatment are crucial for the estimation of temperature of exposure in forensic and archaeological studies. However, at present, only limited data exist on the heat-induced structural alterations of human dental tissues. In this paper, advanced non-destructive small- and wide angle X-ray scattering (SAXS/WAXS) synchrotron techniques were used to investigate the in situ ultrastructural alterations in thermally treated human dental tissues and synthetic HAp powders. The crystallographic properties were probed by WAXS, whereas HAp grain size distribution changes were evaluated by SAXS. The results demonstrate the important role of the organic matrix that binds together the HAp crystallites in responding to heat exposure. This is highlighted by the difference in the thermal behaviour between human dental tissues and synthetic HAp powders. The X-ray analysis results are supported by thermogravimetric analysis. The results concerning the HAp crystalline architecture in natural and synthetic HAp powders provide a reliable basis for deducing the heating history for dental tissues in the forensic and archaeological context, and the foundation for further development and optimization of biomimetic material design

Structure-property characterization of the dentine-enamel junction (DEJ)

The dentine-enamel junction (DEJ) is an Important internal interface with strong and durable bonding between the hard outer layer (enamel) and the soft inner tooth core (dentine). This study investigated the microstructure of the DEJ by X-ray imaging method and synchrotron X-ray scattering techniques. Further high resolution elastic modulus mapping indicates that the DEJ is a band with a graded mechanical property rather than a discrete interface. The microstructure-property relationship is also illustrated. The knowledge of the architecture and properties of the natural DEJ will help in the biomimetic development of dental restorations and novel replacement materials and application techniques