不过洗牙次数再多也不能去除由于四环素或系统性疾病导致的牙齿深度着色，因为这些色素已进入你的牙齿内部，你需要采取更加积极地措施来对付它们。
No amount of cleaning will remove the severe staining left by tetracycline or systemic disease because these pigments lie inside the tooth; you'll have to take more aggressive measures against these.
其中包括去除好几层土壤，直到某个合适的深度。
It includes delayering the soil several layers to a certain depth.
深度的划痕是无法弥补的，并且在很多情况下是不能去除的。
Deep scratches cannot be filled in and in some cases cannot be removed.
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