齲齒是一種最常見的口腔疾病，其形成原因來自於一些致齲菌產生酸而侵蝕牙齒。變異鏈球菌(Streptococcus mutans)是最主要造成齲齒的病原菌，經由代謝醣類產生酸後造成牙齒組織去礦化。然而，並不是所有口腔中的細菌都會造成齲齒，許多口腔中的細菌可以與致齲菌的菌落相抗衡，進而保護牙齒免於形成齲齒。因此，開發有效的抗齲物質是一個重要的課題，其必須能夠抑制致齲菌的生長，並且保護不會造成齲齒的益菌，進而維護口腔中菌落的平衡。氫氧基磷灰石是骨骼和牙齒的主要成分，常被運用在各種層面，包含生醫材料、組織工程和藥物釋放等等。在過去的研究中，要形成球狀的氫氧基磷灰石，一些有機的分子或聚合物扮演很重要的角色，其會經由在溶液中形成特殊結構的微胞而形成。然而，現在只需透過離子就可以幫助礦化，不需要任何的界面活性劑，就能在溶液中製備含有氟離子的氟基磷灰石。這些合成出來的氟基磷灰石的性質經由高解析熱電子型場發射掃描式電子顯微鏡、X光繞射儀和傅里葉轉換紅外光譜來分析，也藉由氟離子電極偵測氟離子的釋放，發現氟基磷灰石在酸性溶液中的氟離子釋放程度比中性溶液要高。另外，藉由菌落形成單位的檢測可以進一步去分析氟基磷灰石對於變異鏈球菌和格氏鏈球菌(Streptococcus gordonii)的抗菌能力，結果顯示這些氟基磷灰石不只能有效地抑制致齲菌的生長並且能同時保護口腔中的益菌，而這種結果在牙齒琺瑯質的切片上也可以由高解析熱電子型場發射掃描式電子顯微鏡觀察到。這提供了一個新的想法去開發這種智慧型抗齲的奈米粒子，若能將這些粒子加入牙膏，將會是未來口腔預防照護的新途徑。

Caries is one of the most popular oral diseases derived from acid challenge produced by cariogenic bacteria. Streptococcus mutans is the major pathogenic bacteria involved in caries, which can form dental plaque followed by demineralization of tooth mineral tissues. Not all bacteria in oral cavity contribute the development of caries. Instead, many oral bacteria have protective effect to caries development through counter-balance of the cariogenic flora. Therefore, it is important in the design of effective anti-carious strategy that integrates selectivity for cariogenic pathogens inhibition and non-cariogenic bacteria preservation. Hydroxyapatite, as the main mineral component of bones and teeth, has applications as biomaterials, tissue engineering, and drug delivery, etc. In previous study, organic molecules and polymers play an important role in the formation of these spherical hydroxyapatite particles through forming a specific structure of micelles in solution. However, a solution method to prepare fluoride-doped hydroxyapatite (Fluorapatite) with hierarchical structure via an ion-assisted and surfactant-free mineralization process has been employed. High-resolution thermal field emission scanning electron microscope (FE-SEM), X-ray diffraction and Fourier transform infrared spectroscope were used to characterize the derived particles. The fluoride release of fluorapatite particles was evaluated by fluoride ion electrode. The fluoride release concentration was higher in acidic environment than in neutral. Further, the antibacterial activity of the particles was evaluated in S. mutans and S. gordonii by colony forming unit assay. The results showed fluorapatite could not only selectively suppress cariogenic bacteria but protect the probiotics of the oral cavity. We also confirmed the differential antibacterial activity in an ex vivo model using human tooth enamel slab by FE-SEM. These nanoparticles provide a new concept to develop smart anti-caries strategy as the nanoparticles not only protect teeth against the threat of cariogenic bacteria but also protect the probiotics.

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