The oral surfaces covered in keratinized epithelium include the hard palate, the dorsal surface, or top, of the tongue, and the gingiva.

口腔表面由角化上的结构包括硬腭、舌的背侧面（或上面）与牙龈。

But that is when you get infection of the tongue, the oral mucosa, the gingiva, so your gums or your throat or esophagus.

但这种情况发生在舌头、口腔粘膜、牙龈，也你的牙龈或喉咙或食道感染时。

If the gingiva recedes or plaque forms between the gingiva and the root, bacteria and acids have direct access to the cementum, which is much softer than enamel and dissolves more quickly.

如果牙龈退缩或牙龈和牙根间形成牙斑，细菌和酸直接侵犯牙骨质，与牙釉质相比牙骨质更软，溶解更快。

The crown is the visible part of the tooth that protrudes from the gingiva, and it's covered in enamel, which has such a high mineral content that it's the hardest substance in the human body.

牙冠牙齿突出牙龈，被直视的部分，它被牙釉质；牙釉质的矿物质含量极高，人体最坚硬的组织。