That's because hydrogen peroxide soaks through the protective outer coating of enamel and into the softer layer of dentin underneath, irritating the nerve-rich dental pulp at the core.
这是因为过氧化氢会渗入釉质的外部保护层并进入牙质下面的较为柔软的一层，刺激神经组织比较多的牙髓。
As we age, the outer layer of tooth enamel wears away.
随着年龄增长，我们牙齿外层的釉质会慢慢地磨损。
Outer layer of the tooth enamel and ivory to protect the pulp quality.
牙齿的外层有珐琅质及象牙质来保护牙髓。
Outer layer of the tooth enamel and ivory to protect the pulp quality.
牙齿的外层有珐琅质及象牙质来保护牙髓。
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