Trimby Patrick, Al-Mosawi Mohammed, Al-Jawad Maisoon, Micklethwaite Stuart, Aslam Zabeada, Winkelmann Aimo, Piazolo Sandra
Oxford Instruments Nanoanalysis, High Wycombe, Buckinghamshire, UK; Carl Zeiss Ltd., Cambourne, Cambridge, UK.
School of Dentistry, University of Leeds, Leeds, West Yorkshire, UK.
Ultramicroscopy. 2024 Jun;260:113940. doi: 10.1016/j.ultramic.2024.113940. Epub 2024 Feb 24.
The remarkable physical properties of dental enamel can be largely attributed to the structure of the hydroxyapatite (HAp) crystallites on the sub-micrometre scale. Characterising the HAp microstructure is challenging, due to the nanoscale of individual crystallites and practical challenges associated with HAp examination using electron microscopy techniques. Conventional methods for enamel characterisation include imaging using transmission electron microscopy (TEM) or specialised beamline techniques, such as polarisation-dependent imaging contrast (PIC). These provide useful information at the necessary spatial resolution but are not able to measure the full crystallographic orientation of the HAp crystallites. Here we demonstrate the effectiveness of enamel analyses using transmission Kikuchi diffraction (TKD) in the scanning electron microscope, coupled with newly-developed pattern matching methods. The pattern matching approach, using dynamic template matching coupled with subsequent orientation refinement, enables robust indexing of even poor-quality TKD patterns, resulting in significantly improved data quality compared to conventional diffraction pattern indexing methods. The potential of this method for the analysis of nanocrystalline enamel structures is demonstrated by the characterisation of a human enamel TEM sample and the subsequent comparison of the results to high resolution TEM imaging. The TKD - pattern matching approach measures the full HAp crystallographic orientation enabling a quantitative measurement of not just the c-axis orientations, but also the extent of any rotation of the crystal lattice about the c-axis, between and within grains. Results presented here show how this additional information highlights potentially significant aspects of the HAp crystallite structure, including intra-crystallite distortion and the presence of multiple high angle boundaries between adjacent crystallites with rotations about the c-axis. These and other observations enable a more rigorous understanding of the relationship between HAp structures and the physical properties of dental enamel.
牙釉质卓越的物理特性在很大程度上可归因于亚微米尺度下羟基磷灰石（HAp）微晶的结构。由于单个微晶的纳米尺度以及使用电子显微镜技术检查HAp所面临的实际挑战，表征HAp微观结构具有挑战性。牙釉质表征的传统方法包括使用透射电子显微镜（TEM）成像或专门的束线技术，如偏振依赖成像对比度（PIC）。这些方法在必要的空间分辨率下提供了有用信息，但无法测量HAp微晶的完整晶体取向。在此，我们展示了在扫描电子显微镜中使用透射菊池衍射（TKD）结合新开发的模式匹配方法进行牙釉质分析的有效性。该模式匹配方法使用动态模板匹配并随后进行取向细化，即使对于质量较差的TKD图案也能实现稳健的索引，与传统衍射图案索引方法相比，数据质量得到显著提高。通过对人类牙釉质TEM样品的表征以及随后将结果与高分辨率TEM成像进行比较，证明了该方法在分析纳米晶牙釉质结构方面的潜力。TKD - 模式匹配方法测量HAp的完整晶体取向，不仅能够定量测量c轴取向，还能测量晶粒之间和晶粒内部晶格围绕c轴的任何旋转程度。此处呈现的结果表明，这些额外信息如何突出了HAp微晶结构潜在的重要方面，包括微晶内畸变以及相邻微晶之间存在的多个围绕c轴旋转的高角度边界。这些及其他观察结果有助于更深入地理解HAp结构与牙釉质物理特性之间的关系。
