The enamel layer of a tooth is made up of hydroxyapatite crystals, which form microscopic "rods".

牙齿最外层的牙釉质是由我们肉眼看不到的显微小管所组成的。

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Teeth have a hard surface layer called enamel.

牙齿有一层叫做釉质的坚硬表层。

《牛津词典》

Inner enamel is mainly composed of ceramic layer and special enamelled steel two materials.

搪瓷内胆主要有瓷层及专用搪瓷钢板两种材料组成。

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The constant exposure strips the hard, protective layer of the tooth called the enamel and could dissolve the entire tooth.

CNN: Juices, tea and energy drinks erode teeth

Tooth enamel begins to form in the human embryo when a specialised layer of cells, called ameloblasts, in the embryonic tooth bud secretes amelogenin proteins.

BBC: By BBC News Online Science Editor Dr David Whitehouse