Recent advances in atomic force microscopy (AFM) have allowed the characterisation of dental-associated biomaterials and biological surfaces with high resolution. In this context, the topography of dental enamel – the hardest mineralised tissue in the body – has been explored with AFM-based approaches at the microscale. With age, teeth are known to suffer changes that can impact their structural stability and function; however, changes in enamel structure because of ageing have not yet been explored with nanoscale resolution. Therefore, the aim of this exploratory work was to optimise an approach to characterise the ultrastructure of dental enamel and determine potential differences in topography, hydroxyapatite (HA) crystal size, and surface roughness at the nanoscale associated to ageing. For this, a total of six teeth were collected from human donors from which enamel specimens were prepared. By employing intermittent contact (AC mode) imaging, HA crystals were characterised in both transversal and longitudinal orientation (respect to surface plane) with high resolution in environmental conditions. The external enamel surface displayed the presence of a pellicle-like coating on its surface that was not observable on cleaned specimens. Acid-etching exposed crystals that were imaged and morphologically characterised in high resolution at the nanoscale in both the external and internal regions of enamel in older and younger specimens. Our results demonstrated important individual variations in HA crystal width and roughness parameters across the analysed specimens; however, an increase in surface roughness and decrease in HA width was observed for the pooled older external enamel group compared to younger specimens. Overall, high-resolution AFM was an effective approach for the qualitative and quantitative characterisation of human dental enamel ultrastructure. Future work should focus on exploring the ageing of dental enamel with increased sample sizes to compensate for individual differences as well as other potential confounding factors such as behavioural habits and mechanical forces.

中文翻译：

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原子力显微镜对年轻和老年牙釉质的超微结构表征

原子力显微镜 (AFM) 的最新进展允许以高分辨率表征牙科相关生物材料和生物表面。在这种情况下，牙釉质（人体中最坚硬的矿化组织）的形貌已经通过基于 AFM 的方法在微观尺度上进行了探索。众所周知，随着年龄的增长，牙齿会发生变化，从而影响其结构稳定性和功能；然而，尚未以纳米级分辨率探索因老化而导致的牙釉质结构变化。因此，这项探索性工作的目的是优化一种方法来表征牙釉质的超微结构，并确定与老化相关的纳米级形貌、羟基磷灰石 (HA) 晶体尺寸和表面粗糙度的潜在差异。为了这，总共从人类捐献者那里收集了六颗牙齿，并从中制备了牙釉质标本。通过采用间歇接触（AC 模式）成像，HA 晶体在环境条件下具有高分辨率的横向和纵向（相对于表面平面）特征。外搪瓷表面显示出在其表面上存在一层薄膜状涂层，这在清洁过的样品上是观察不到的。酸蚀刻暴露的晶体在较旧和较新标本的牙釉质的外部和内部区域以纳米级高分辨率成像和形态特征。我们的结果表明，在分析的样本中，HA 晶体宽度和粗糙度参数存在重要的个体差异；然而，与较年轻的标本相比，合并的较旧外釉质组的表面粗糙度增加，HA 宽度减小。总体而言，高分辨率 AFM 是定性和定量表征人牙釉质超微结构的有效方法。未来的工作应侧重于探索牙釉质的老化，增加样本量以补偿个体差异以及其他潜在的混杂因素，如行为习惯和机械力。